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Lal MK, Sharma N, Adavi SB, Sharma E, Altaf MA, Tiwari RK, Kumar R, Kumar A, Dey A, Paul V, Singh B, Singh MP. From source to sink: mechanistic insight of photoassimilates synthesis and partitioning under high temperature and elevated [CO 2]. PLANT MOLECULAR BIOLOGY 2022; 110:305-324. [PMID: 35610527 DOI: 10.1007/s11103-022-01274-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Accepted: 04/10/2022] [Indexed: 05/27/2023]
Abstract
Photosynthesis is the vital metabolism of the plant affected by abiotic stress such as high temperature and elevated [CO2] levels, which ultimately affect the source-sink relationship. Triose phosphate, the primary precursor of carbohydrate (starch and sucrose) synthesis in the plant, depends on environmental cues. The synthesis of starch in the chloroplasts of leaves (during the day), the transport of photoassimilates (sucrose) from source to sink, the loading and unloading of photoassimilates, and the accumulation of starch in the sink tissue all require a highly regulated network and communication system within the plant. These processes might be affected by high-temperature stress and elevated [CO2] conditions. Generally, elevated [CO2] levels enhance plant growth, photosynthetic rate, starch synthesis, and accumulation, ultimately diluting the nutrient of sink tissues. On the contrary, high-temperature stress is detrimental to plant development affecting photosynthesis, starch synthesis, sucrose synthesis and transport, and photoassimilate accumulation in sink tissues. Moreover, these environmental conditions also negatively impact the quality attributes such as grain/tuber quality, cooking quality, nutritional status in the edible parts and organoleptic traits. In this review, we have attempted to provide an insight into the source-sink relationship and the sugar metabolites synthesized and utilized by the plant under elevated [CO2] and high-temperature stress. This review will help future researchers comprehend the source-sink process for crop growth under changing climate scenarios.
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Affiliation(s)
- Milan Kumar Lal
- ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India
- ICAR-Central Potato Research Institute, Shimla, Himachal Pradesh, 171001, India
| | - Nitin Sharma
- ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India
- Dr Yashwant, Singh Parmar University of Horticulture & Forestry, Nauni, Solan, Himachal Pradesh, 173230, India
| | - Sandeep B Adavi
- ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India
| | - Eshita Sharma
- Dietetics & Nutrition Technology Division, CSIR-Institute of Himalayan Bioresource Technology, Palampur, Himachal Pradesh, 176061, India
- Department of Molecular Biology and Biochemistry, Guru Nanak Dev University, Amritsar, India
| | | | - Rahul Kumar Tiwari
- ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India.
- ICAR-Central Potato Research Institute, Shimla, Himachal Pradesh, 171001, India.
| | - Ravinder Kumar
- ICAR-Central Potato Research Institute, Shimla, Himachal Pradesh, 171001, India.
| | - Awadhesh Kumar
- ICAR-National Rice Research Institute, Cuttack, Odisha, 753006, India
| | - Abhijit Dey
- Department of Life Sciences, Presidency University, 86/1 College Street, Kolkata, West Bengal, 700073, India
| | - Vijay Paul
- ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India
| | - Brajesh Singh
- ICAR-Central Potato Research Institute, Shimla, Himachal Pradesh, 171001, India
| | - Madan Pal Singh
- ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India.
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Qin Y, Xiao Z, Zhao H, Wang J, Wang Y, Qiu F. Starch phosphorylase 2 is essential for cellular carbohydrate partitioning in maize. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2022; 64:1755-1769. [PMID: 35796344 DOI: 10.1111/jipb.13328] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Accepted: 07/06/2022] [Indexed: 06/15/2023]
Abstract
Carbohydrate partitioning is essential for plant growth and development, and its hindrance will result in excess accumulation of carbohydrates in source tissues. Most of the related mutants in maize (Zea mays L.) display impaired whole-plant sucrose transport, but other mechanisms affecting carbohydrate partitioning have seldom been reported. Here, we characterized chlorotic leaf3 (chl3), a recessive mutation causing leaf chlorosis with starch accumulation excessively in bundle sheath chloroplasts, suggesting that chl3 is defective in carbohydrate partitioning. Positional cloning revealed that the chl3 phenotype results from a frameshift mutation in ZmPHOH, which encodes starch phosphorylase 2. Two mutants in ZmPHOH exhibited the same phenotype as chl3, and both alleles failed to complement the chl3 mutant phenotype in an allelism test. Inactivation of ZmPHOH in chl3 leaves reduced the efficiency of transitory starch conversion, resulting in increased leaf starch contents and altered carbohydrate metabolism patterns. RNA-seq revealed the transcriptional downregulation of genes related to photosynthesis and carbohydrate metabolism in chl3 leaves compared to the wild type. Our results demonstrate that transitory starch remobilization is very important for cellular carbohydrate partitioning in maize, in which ZmPHOH plays an indispensable role.
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Affiliation(s)
- Yao Qin
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China
| | - Ziyi Xiao
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China
| | - Hailiang Zhao
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China
| | - Jing Wang
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China
| | - Yuanru Wang
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China
| | - Fazhan Qiu
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China
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Wang Y, Sun J, Deng C, Teng S, Chen G, Chen Z, Cui X, Brutnell TP, Han X, Zhang Z, Lu T. Plasma membrane-localized SEM1 protein mediates sugar movement to sink rice tissues. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2022; 109:523-540. [PMID: 34750914 DOI: 10.1111/tpj.15573] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Accepted: 11/01/2021] [Indexed: 06/13/2023]
Abstract
The translocation of photosynthate carbohydrates, such as sucrose, is critical for plant growth and crop yield. Previous studies have revealed that sugar transporters, plasmodesmata and sieve plates act as important controllers in sucrose loading into and unloading from phloem in the vascular system. However, other pivotal steps for the regulation of sucrose movement remain largely elusive. In this study, characterization of two starch excesses in mesophyll (sem) mutants and dye and sucrose export assays were performed to provide insights into the regulatory networks that drive source-sink relations in rice. Map-based cloning identified two allelic mutations in a gene encoding a GLUCAN SYNTHASE-LIKE (GSL) protein, thus indicating a role for SEM1 in callose biosynthesis. Subcellular localization in rice showed that SEM1 localized to the plasma membrane. In situ expression analysis and GUS staining showed that SEM1 was mainly expressed in vascular phloem cells. Reduced sucrose transport was found in the sem1-1/1-2 mutant, which led to excessive starch accumulation in source leaves and inhibited photosynthesis. Paraffin section and transmission electron microscopy experiments revealed that less-developed vascular cells (VCs) in sem1-1/1-2 potentially disturbed sugar movement. Moreover, dye and sugar trafficking experiments revealed that aberrant VC development was the main reason for the pleiotropic phenotype of sem1-1/1-2. In total, efficient sucrose loading into the phloem benefits from an optional number of VCs with a large vacuole that could act as a buffer holding tank for sucrose passing from the vascular bundle sheath.
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Affiliation(s)
- Yanwei Wang
- Joint CAAS/IRRI Laboratory for Photosynthetic Enhancement, Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences, Beijing, 100081, P. R. China
| | - Jing Sun
- Joint CAAS/IRRI Laboratory for Photosynthetic Enhancement, Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences, Beijing, 100081, P. R. China
| | - Chen Deng
- Joint CAAS/IRRI Laboratory for Photosynthetic Enhancement, Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences, Beijing, 100081, P. R. China
| | - Shouzhen Teng
- Joint CAAS/IRRI Laboratory for Photosynthetic Enhancement, Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences, Beijing, 100081, P. R. China
| | - Guoxin Chen
- Joint CAAS/IRRI Laboratory for Photosynthetic Enhancement, Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences, Beijing, 100081, P. R. China
| | - Zhenhua Chen
- Joint CAAS/IRRI Laboratory for Photosynthetic Enhancement, Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences, Beijing, 100081, P. R. China
| | - Xuean Cui
- Joint CAAS/IRRI Laboratory for Photosynthetic Enhancement, Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences, Beijing, 100081, P. R. China
| | - Thomas P Brutnell
- Joint CAAS/IRRI Laboratory for Photosynthetic Enhancement, Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences, Beijing, 100081, P. R. China
| | - Xiao Han
- Joint CAAS/IRRI Laboratory for Photosynthetic Enhancement, Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences, Beijing, 100081, P. R. China
- College of Biological Science and Engineering, Fuzhou University, Fuzhou, 350108, China
| | - Zhiguo Zhang
- Joint CAAS/IRRI Laboratory for Photosynthetic Enhancement, Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences, Beijing, 100081, P. R. China
| | - Tiegang Lu
- Joint CAAS/IRRI Laboratory for Photosynthetic Enhancement, Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences, Beijing, 100081, P. R. China
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Julius BT, McCubbin TJ, Mertz RA, Baert N, Knoblauch J, Grant DG, Conner K, Bihmidine S, Chomet P, Wagner R, Woessner J, Grote K, Peevers J, Slewinski TL, McCann MC, Carpita NC, Knoblauch M, Braun DM. Maize Brittle Stalk2-Like3, encoding a COBRA protein, functions in cell wall formation and carbohydrate partitioning. THE PLANT CELL 2021; 33:3348-3366. [PMID: 34323976 PMCID: PMC8505866 DOI: 10.1093/plcell/koab193] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Accepted: 07/16/2021] [Indexed: 05/14/2023]
Abstract
Carbohydrate partitioning from leaves to sink tissues is essential for plant growth and development. The maize (Zea mays) recessive carbohydrate partitioning defective28 (cpd28) and cpd47 mutants exhibit leaf chlorosis and accumulation of starch and soluble sugars. Transport studies with 14C-sucrose (Suc) found drastically decreased export from mature leaves in cpd28 and cpd47 mutants relative to wild-type siblings. Consistent with decreased Suc export, cpd28 mutants exhibited decreased phloem pressure in mature leaves, and altered phloem cell wall ultrastructure in immature and mature leaves. We identified the causative mutations in the Brittle Stalk2-Like3 (Bk2L3) gene, a member of the COBRA family, which is involved in cell wall development across angiosperms. None of the previously characterized COBRA genes are reported to affect carbohydrate export. Consistent with other characterized COBRA members, the BK2L3 protein localized to the plasma membrane, and the mutants condition a dwarf phenotype in dark-grown shoots and primary roots, as well as the loss of anisotropic cell elongation in the root elongation zone. Likewise, both mutants exhibit a significant cellulose deficiency in mature leaves. Therefore, Bk2L3 functions in tissue growth and cell wall development, and this work elucidates a unique connection between cellulose deposition in the phloem and whole-plant carbohydrate partitioning.
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Affiliation(s)
- Benjamin T Julius
- Divisions of Plant Science and Technology, Biological Sciences, Interdisciplinary Plant Group, and the Missouri Maize Center, University of Missouri, Columbia, Missouri 65211, USA
- Bayer Crop Science, Chesterfield, Missouri 63017, USA
| | - Tyler J McCubbin
- Divisions of Plant Science and Technology, Biological Sciences, Interdisciplinary Plant Group, and the Missouri Maize Center, University of Missouri, Columbia, Missouri 65211, USA
| | - Rachel A Mertz
- Divisions of Plant Science and Technology, Biological Sciences, Interdisciplinary Plant Group, and the Missouri Maize Center, University of Missouri, Columbia, Missouri 65211, USA
- Present address: Inari Agriculture, West Lafayette, Indiana 47906, USA
| | - Nick Baert
- Divisions of Plant Science and Technology, Biological Sciences, Interdisciplinary Plant Group, and the Missouri Maize Center, University of Missouri, Columbia, Missouri 65211, USA
| | - Jan Knoblauch
- School of Biological Sciences, Washington State University, Pullman, Washington 99164, USA
| | - DeAna G Grant
- Electron Microscopy Core Facility, University of Missouri, Columbia, Missouri 65211, USA
| | - Kyle Conner
- Divisions of Plant Science and Technology, Biological Sciences, Interdisciplinary Plant Group, and the Missouri Maize Center, University of Missouri, Columbia, Missouri 65211, USA
| | - Saadia Bihmidine
- Divisions of Plant Science and Technology, Biological Sciences, Interdisciplinary Plant Group, and the Missouri Maize Center, University of Missouri, Columbia, Missouri 65211, USA
| | - Paul Chomet
- NRGene Inc., 8910 University Center Lane, San Diego, California 92122, USA
| | - Ruth Wagner
- Bayer Crop Science, Chesterfield, Missouri 63017, USA
| | - Jeff Woessner
- Bayer Crop Science, Chesterfield, Missouri 63017, USA
| | - Karen Grote
- Bayer Crop Science, Chesterfield, Missouri 63017, USA
| | | | | | - Maureen C McCann
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA
- Purdue Center for Plant Biology, Purdue University, West Lafayette, Indiana 47907, USA
| | - Nicholas C Carpita
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA
- Purdue Center for Plant Biology, Purdue University, West Lafayette, Indiana 47907, USA
- Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907, USA
| | - Michael Knoblauch
- School of Biological Sciences, Washington State University, Pullman, Washington 99164, USA
| | - David M Braun
- Divisions of Plant Science and Technology, Biological Sciences, Interdisciplinary Plant Group, and the Missouri Maize Center, University of Missouri, Columbia, Missouri 65211, USA
- Author for correspondence:
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5
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Azim MF, Burch-Smith TM. Organelles-nucleus-plasmodesmata signaling (ONPS): an update on its roles in plant physiology, metabolism and stress responses. CURRENT OPINION IN PLANT BIOLOGY 2020; 58:48-59. [PMID: 33197746 DOI: 10.1016/j.pbi.2020.09.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Revised: 09/26/2020] [Accepted: 09/27/2020] [Indexed: 05/03/2023]
Abstract
Plasmodesmata allow movement of metabolites and signaling molecules between plant cells and are, therefore, critical players in plant development and physiology, and in responding to environmental signals and stresses. There is emerging evidence that plasmodesmata are controlled by signaling originating from other organelles, primarily the chloroplasts and mitochondria. These signals act in the nucleus to alter expression of genetic pathways that control both trafficking via plasmodesmata and the plasmodesmatal pores themselves. This control circuit was dubbed organelle-nucleus-plasmodesmata signaling (ONPS). Here we discuss how ONPS arose during plant evolution and highlight the discovery of an ONPS-like module for regulating stomata. We also consider recent findings that illuminate details of the ONPS circuit and its roles in plant physiology, metabolism, and defense.
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Affiliation(s)
- Mohammad F Azim
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, United States
| | - Tessa M Burch-Smith
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, United States.
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6
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Interaction Between Induced and Natural Variation at oil yellow1 Delays Reproductive Maturity in Maize. G3-GENES GENOMES GENETICS 2020; 10:797-810. [PMID: 31822516 PMCID: PMC7003087 DOI: 10.1534/g3.119.400838] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
We previously demonstrated that maize (Zea mays) locus very oil yellow1 (vey1) encodes a putative cis-regulatory expression polymorphism at the magnesium chelatase subunit I gene (aka oil yellow1) that strongly modifies the chlorophyll content of the semi-dominant Oy1-N1989 mutants. The vey1 allele of Mo17 inbred line reduces chlorophyll content in the mutants leading to reduced photosynthetic output. Oy1-N1989 mutants in B73 reached reproductive maturity four days later than wild-type siblings. Enhancement of Oy1-N1989 by the Mo17 allele at the vey1 QTL delayed maturity further, resulting in detection of a flowering time QTL in two bi-parental mapping populations crossed to Oy1-N1989. The near isogenic lines of B73 harboring the vey1 allele from Mo17 delayed flowering of Oy1-N1989 mutants by twelve days. Just as previously observed for chlorophyll content, vey1 had no effect on reproductive maturity in the absence of the Oy1-N1989 allele. Loss of chlorophyll biosynthesis in Oy1-N1989 mutants and enhancement by vey1 reduced CO2 assimilation. We attempted to separate the effects of photosynthesis on the induction of flowering from a possible impact of chlorophyll metabolites and retrograde signaling by manually reducing leaf area. Removal of leaves, independent of the Oy1-N1989 mutant, delayed flowering but surprisingly reduced chlorophyll contents of emerging leaves. Thus, defoliation did not completely separate the identity of the signal(s) that regulates flowering time from changes in chlorophyll content in the foliage. These findings illustrate the necessity to explore the linkage between metabolism and the mechanisms that connect it to flowering time regulation.
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Tran TM, McCubbin TJ, Bihmidine S, Julius BT, Baker RF, Schauflinger M, Weil C, Springer N, Chomet P, Wagner R, Woessner J, Grote K, Peevers J, Slewinski TL, Braun DM. Maize Carbohydrate Partitioning Defective33 Encodes an MCTP Protein and Functions in Sucrose Export from Leaves. MOLECULAR PLANT 2019; 12:1278-1293. [PMID: 31102785 DOI: 10.1016/j.molp.2019.05.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Revised: 04/09/2019] [Accepted: 05/03/2019] [Indexed: 05/29/2023]
Abstract
To sustain plant growth, development, and crop yield, sucrose must be transported from leaves to distant parts of the plant, such as seeds and roots. To identify genes that regulate sucrose accumulation and transport in maize (Zea mays), we isolated carbohydrate partitioning defective33 (cpd33), a recessive mutant that accumulated excess starch and soluble sugars in mature leaves. The cpd33 mutants also exhibited chlorosis in the leaf blades, greatly diminished plant growth, and reduced fertility. Cpd33 encodes a protein containing multiple C2 domains and transmembrane regions. Subcellular localization experiments showed the CPD33 protein localized to plasmodesmata (PD), the plasma membrane, and the endoplasmic reticulum. We also found that a loss-of-function mutant of the CPD33 homolog in Arabidopsis, QUIRKY, had a similar carbohydrate hyperaccumulation phenotype. Radioactively labeled sucrose transport assays showed that sucrose export was significantly lower in cpd33 mutant leaves relative to wild-type leaves. However, PD transport in the adaxial-abaxial direction was unaffected in cpd33 mutant leaves. Intriguingly, transmission electron microscopy revealed fewer PD at the companion cell-sieve element interface in mutant phloem tissue, providing a possible explanation for the reduced sucrose export in mutant leaves. Collectively, our results suggest that CPD33 functions to promote symplastic transport into sieve elements.
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Affiliation(s)
- Thu M Tran
- Division of Biological Sciences, Interdisciplinary Plant Group, Missouri Maize Center, University of Missouri, Columbia, MO 65211, USA; Division of Plant Sciences, University of Missouri, Columbia, MO 65211, USA; National Key Laboratory for Plant Cell Technology, Agricultural Genetics Institute, Hanoi, Vietnam
| | - Tyler J McCubbin
- Division of Biological Sciences, Interdisciplinary Plant Group, Missouri Maize Center, University of Missouri, Columbia, MO 65211, USA; Division of Plant Sciences, University of Missouri, Columbia, MO 65211, USA
| | - Saadia Bihmidine
- Division of Biological Sciences, Interdisciplinary Plant Group, Missouri Maize Center, University of Missouri, Columbia, MO 65211, USA
| | - Benjamin T Julius
- Division of Biological Sciences, Interdisciplinary Plant Group, Missouri Maize Center, University of Missouri, Columbia, MO 65211, USA
| | - R Frank Baker
- Division of Biological Sciences, Interdisciplinary Plant Group, Missouri Maize Center, University of Missouri, Columbia, MO 65211, USA
| | - Martin Schauflinger
- Electron Microscopy Core Facility, University of Missouri, Columbia, MO 65211, USA
| | - Clifford Weil
- Department of Agronomy, Purdue University, West Lafayette, IN 47907, USA
| | - Nathan Springer
- Department of Plant and Microbial Biology, University of Minnesota, Saint Paul, MN 55108, USA
| | - Paul Chomet
- NRGene Inc., 8910 University Center Lane, ∖r∖nSuite 400, San Diego, CA 92122, USA
| | - Ruth Wagner
- Bayer Crop Science, Chesterfield, MO 63017, USA
| | | | - Karen Grote
- Bayer Crop Science, Chesterfield, MO 63017, USA
| | | | | | - David M Braun
- Division of Biological Sciences, Interdisciplinary Plant Group, Missouri Maize Center, University of Missouri, Columbia, MO 65211, USA.
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Wang H, Yan S, Xin H, Huang W, Zhang H, Teng S, Yu YC, Fernie AR, Lu X, Li P, Li S, Zhang C, Ruan YL, Chen LQ, Lang Z. A Subsidiary Cell-Localized Glucose Transporter Promotes Stomatal Conductance and Photosynthesis. THE PLANT CELL 2019; 31:1328-1343. [PMID: 30996077 PMCID: PMC6588317 DOI: 10.1105/tpc.18.00736] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Revised: 03/21/2019] [Accepted: 04/17/2019] [Indexed: 05/04/2023]
Abstract
It has long been recognized that stomatal movement modulates CO2 availability and as a consequence the photosynthetic rate of plants, and that this process is feedback-regulated by photoassimilates. However, the genetic components and mechanisms underlying this regulatory loop remain poorly understood, especially in monocot crop species. Here, we report the cloning and functional characterization of a maize (Zea mays) mutant named closed stomata1 (cst1). Map-based cloning of cst1 followed by confirmation with the clustered regularly interspaced short palindromic repeats (CRISPR)/ CRISPR associated protein 9 system identified the causal mutation in a Clade I Sugars Will Eventually be Exported Transporters (SWEET) family gene, which leads to the E81K mutation in the CST1 protein. CST1 encodes a functional glucose transporter expressed in subsidiary cells, and the E81K mutation strongly impairs the oligomerization and glucose transporter activity of CST1. Mutation of CST1 results in reduced stomatal opening, carbon starvation, and early senescence in leaves, suggesting that CST1 functions as a positive regulator of stomatal opening. Moreover, CST1 expression is induced by carbon starvation and suppressed by photoassimilate accumulation. Our study thus defines CST1 as a missing link in the feedback-regulation of stomatal movement and photosynthesis by photoassimilates in maize.
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Affiliation(s)
- Hai Wang
- Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R. China
| | - Shijuan Yan
- Agro-biological Gene Research Center, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, P.R. China
| | - Hongjia Xin
- Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R. China
| | - Wenjie Huang
- Agro-biological Gene Research Center, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, P.R. China
| | - Hao Zhang
- Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R. China
| | - Shouzhen Teng
- Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R. China
| | - Ya-Chi Yu
- Department of Plant Biology, School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Alisdair R. Fernie
- Max-Planck-Institute of Molecular Plant Physiology, Am Muhlenberg 1, Potsdam-Golm 14476, Germany
| | - Xiaoduo Lu
- National Engineering Laboratory of Crop Stress Resistance Breeding, Anhui Agricultural University, Hefei 230036, P.R. China
| | - Pengcheng Li
- Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R. China
| | - Shengyan Li
- Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R. China
| | - Chunyi Zhang
- Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R. China
| | - Yong-Ling Ruan
- School of Environmental & Life Sciences, The University of Newcastle, Callaghan NSW 2308, Australia
| | - Li-Qing Chen
- Department of Plant Biology, School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Zhihong Lang
- Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R. China
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Julius BT, Slewinski TL, Baker RF, Tzin V, Zhou S, Bihmidine S, Jander G, Braun DM. Maize Carbohydrate partitioning defective1 impacts carbohydrate distribution, callose accumulation, and phloem function. JOURNAL OF EXPERIMENTAL BOTANY 2018; 69:3917-3931. [PMID: 29846660 PMCID: PMC6054164 DOI: 10.1093/jxb/ery203] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Accepted: 05/18/2018] [Indexed: 05/19/2023]
Abstract
Plants synthesize carbohydrates in photosynthetic tissues, with the majority of plants transporting sucrose to non-photosynthetic tissues to sustain growth and development. While the anatomical, biochemical, and physiological processes regulating sucrose long-distance transport are well characterized, little is known concerning the genes controlling whole-plant carbohydrate partitioning. To identify loci influencing carbon export from leaves, we screened mutagenized maize plants for phenotypes associated with reduced carbohydrate transport, including chlorosis and excessive starch and soluble sugars in leaves. Carbohydrate partitioning defective1 (Cpd1) was identified as a semi-dominant mutant exhibiting these phenotypes. Phloem transport experiments suggested that the hyperaccumulation of starch and soluble sugars in the Cpd1/+ mutant leaves was due to inhibited sucrose export. Interestingly, ectopic callose deposits were observed in the phloem of mutant leaves, and probably underlie the decreased transport. In addition to the carbohydrate hyperaccumulation phenotype, Cpd1/+ mutants overaccumulate benzoxazinoid defense compounds and exhibit increased tolerance when attacked by aphids. However, double mutant studies between Cpd1/+ and benzoxazinoid-less plants indicate that the ectopic callose and carbon hyperaccumulation are independent of benzoxazinoid production. Based on the formation of callose occlusions in the developing phloem, we hypothesize that the cpd1 gene functions early in phloem development, thereby impacting whole-plant carbohydrate partitioning.
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Affiliation(s)
- Benjamin T Julius
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, MO, USA
| | - Thomas L Slewinski
- Department of Biology, Pennsylvania State University, State College, PA, USA
| | - R Frank Baker
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, MO, USA
| | - Vered Tzin
- Boyce Thompson Institute, Ithaca, NY, USA
| | | | - Saadia Bihmidine
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, MO, USA
| | | | - David M Braun
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, MO, USA
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10
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Ning P, Yang L, Li C, Fritschi FB. Post-silking carbon partitioning under nitrogen deficiency revealed sink limitation of grain yield in maize. JOURNAL OF EXPERIMENTAL BOTANY 2018; 69:1707-1719. [PMID: 29361032 PMCID: PMC5888971 DOI: 10.1093/jxb/erx496] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Accepted: 12/26/2017] [Indexed: 05/24/2023]
Abstract
Maize (Zea mays) plants exhibit altered carbon partitioning under nitrogen (N) deficiency, but the mechanisms by which N availability affects sugar export out of leaves and transport into developing ears remain unclear. Maize was grown under field conditions with different N supply. Plant growth, sugar movement, and starch turnover in source or sink tissues were investigated at silking and 20 or 21 days after silking. Nitrogen deficiency stunted plant growth and grain yield compared with N-sufficient plants, and resulted in greater starch concentrations in leaves due to more as well as larger starch granules in bundle sheath cells. Transmission electron microscopy revealed an open symplastic pathway for sucrose movement in N-deficient leaves, while the expression levels of transporters responsible for sucrose efflux and phloem loading were lower than in N-sufficient leaves. Nonetheless, greater starch concentrations in the apical cob portion of N-deficient plants implied sufficient carbon supply relative to the diminished sink strength (decreased kernel number and weight). Together with the high sugar concentrations in the developing kernels, the results indicated that reduced sink capacity and sugar utilization during grain filling may limit the yield in N-deficient plants, which in turn imposes a feedback inhibition on sugar export from leaves.
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Affiliation(s)
- Peng Ning
- Key Laboratory of Plant-Soil Interactions, Ministry of Education, Department of Plant Nutrition, China Agricultural University, Beijing, China
- College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi, China
- Division of Plant Sciences, University of Missouri, Columbia, USA
| | - Lu Yang
- Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Chunjian Li
- Key Laboratory of Plant-Soil Interactions, Ministry of Education, Department of Plant Nutrition, China Agricultural University, Beijing, China
| | - Felix B Fritschi
- Division of Plant Sciences, University of Missouri, Columbia, USA
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11
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Diepenbrock CH, Kandianis CB, Lipka AE, Magallanes-Lundback M, Vaillancourt B, Góngora-Castillo E, Wallace JG, Cepela J, Mesberg A, Bradbury PJ, Ilut DC, Mateos-Hernandez M, Hamilton J, Owens BF, Tiede T, Buckler ES, Rocheford T, Buell CR, Gore MA, DellaPenna D. Novel Loci Underlie Natural Variation in Vitamin E Levels in Maize Grain. THE PLANT CELL 2017; 29:2374-2392. [PMID: 28970338 PMCID: PMC5774569 DOI: 10.1105/tpc.17.00475] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 08/23/2017] [Accepted: 09/29/2017] [Indexed: 05/19/2023]
Abstract
Tocopherols, tocotrienols, and plastochromanols (collectively termed tocochromanols) are lipid-soluble antioxidants synthesized by all plants. Their dietary intake, primarily from seed oils, provides vitamin E and other health benefits. Tocochromanol biosynthesis has been dissected in the dicot Arabidopsis thaliana, which has green, photosynthetic seeds, but our understanding of tocochromanol accumulation in major crops, whose seeds are nonphotosynthetic, remains limited. To understand the genetic control of tocochromanols in grain, we conducted a joint linkage and genome-wide association study in the 5000-line U.S. maize (Zea mays) nested association mapping panel. Fifty-two quantitative trait loci for individual and total tocochromanols were identified, and of the 14 resolved to individual genes, six encode novel activities affecting tocochromanols in plants. These include two chlorophyll biosynthetic enzymes that explain the majority of tocopherol variation, which was not predicted given that, like most major cereal crops, maize grain is nonphotosynthetic. This comprehensive assessment of natural variation in vitamin E levels in maize establishes the foundation for improving tocochromanol and vitamin E content in seeds of maize and other major cereal crops.
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Affiliation(s)
- Christine H Diepenbrock
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, New York 14853
| | - Catherine B Kandianis
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, New York 14853
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824
| | - Alexander E Lipka
- Institute for Genomic Diversity, Cornell University, Ithaca, New York 14853
| | - Maria Magallanes-Lundback
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824
| | - Brieanne Vaillancourt
- Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824
| | - Elsa Góngora-Castillo
- Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824
| | - Jason G Wallace
- Institute for Genomic Diversity, Cornell University, Ithaca, New York 14853
| | - Jason Cepela
- Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824
| | - Alex Mesberg
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824
| | - Peter J Bradbury
- Institute for Genomic Diversity, Cornell University, Ithaca, New York 14853
- U.S. Department of Agriculture-Agricultural Research Service, Robert W. Holley Center for Agriculture and Health, Ithaca, New York 14853
| | - Daniel C Ilut
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, New York 14853
| | | | - John Hamilton
- Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824
| | - Brenda F Owens
- Department of Agronomy, Purdue University, West Lafayette, IN 47907
| | - Tyler Tiede
- Department of Agronomy, Purdue University, West Lafayette, IN 47907
| | - Edward S Buckler
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, New York 14853
- Institute for Genomic Diversity, Cornell University, Ithaca, New York 14853
- U.S. Department of Agriculture-Agricultural Research Service, Robert W. Holley Center for Agriculture and Health, Ithaca, New York 14853
| | | | - C Robin Buell
- Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824
| | - Michael A Gore
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, New York 14853
| | - Dean DellaPenna
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824
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12
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Leach KA, Tran TM, Slewinski TL, Meeley RB, Braun DM. Sucrose transporter2 contributes to maize growth, development, and crop yield. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2017; 59:390-408. [PMID: 28206710 DOI: 10.1111/jipb.12527] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2016] [Accepted: 02/10/2017] [Indexed: 05/24/2023]
Abstract
During daylight, plants produce excess photosynthates, including sucrose, which is temporarily stored in the vacuole. At night, plants remobilize sucrose to sustain metabolism and growth. Based on homology to other sucrose transporter (SUT) proteins, we hypothesized the maize (Zea mays) SUCROSE TRANSPORTER2 (ZmSUT2) protein functions as a sucrose/H+ symporter on the vacuolar membrane to export transiently stored sucrose. To understand the biological role of ZmSut2, we examined its spatial and temporal gene expression, determined the protein subcellular localization, and characterized loss-of-function mutations. ZmSut2 mRNA was ubiquitously expressed and exhibited diurnal cycling in transcript abundance. Expressing a translational fusion of ZmSUT2 fused to a red fluorescent protein in maize mesophyll cell protoplasts revealed that the protein localized to the tonoplast. Under field conditions, zmsut2 mutant plants grew slower, possessed smaller tassels and ears, and produced fewer kernels when compared to wild-type siblings. zmsut2 mutants also accumulated two-fold more sucrose, glucose, and fructose as well as starch in source leaves compared to wild type. These findings suggest (i) ZmSUT2 functions to remobilize sucrose out of the vacuole for subsequent use in growing tissues; and (ii) its function provides an important contribution to maize development and agronomic yield.
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Affiliation(s)
- Kristen A Leach
- Division of Biological Sciences, Interdisciplinary Plant Group, Missouri Maize Center, University of Missouri, Columbia MO 65211 USA
| | - Thu M Tran
- Division of Biological Sciences, Interdisciplinary Plant Group, Missouri Maize Center, University of Missouri, Columbia MO 65211 USA
| | - Thomas L Slewinski
- Department of Biology, Pennsylvania State University, University Park, PA 16802, USA
| | - Robert B Meeley
- DuPont Pioneer Research & Development, Johnston, Iowa 50131, USA
| | - David M Braun
- Division of Biological Sciences, Interdisciplinary Plant Group, Missouri Maize Center, University of Missouri, Columbia MO 65211 USA
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13
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Tran TM, Hampton CS, Brossard TW, Harmata M, Robertson JD, Jurisson SS, Braun DM. In vivo transport of three radioactive [ 18F]-fluorinated deoxysucrose analogs by the maize sucrose transporter ZmSUT1. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2017; 115:1-11. [PMID: 28300727 DOI: 10.1016/j.plaphy.2017.03.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 03/05/2017] [Accepted: 03/06/2017] [Indexed: 05/26/2023]
Abstract
Sucrose transporter (SUT) proteins translocate sucrose across cell membranes; however, mechanistic aspects of sucrose binding by SUTs are not well resolved. Specific hydroxyl groups in sucrose participate in hydrogen bonding with SUT proteins. We previously reported that substituting a radioactive fluorine-18 [18F] at the C-6' position within the fructosyl moiety of sucrose did not affect sucrose transport by the maize (Zea mays) ZmSUT1 protein. To determine how 18F substitution of hydroxyl groups at two other positions within sucrose, the C-1' in the fructosyl moiety or the C-6 in the glucosyl moiety, impact sucrose transport, we synthesized 1'-[F18]fluoro-1'-deoxysucrose and 6-[F18]fluoro-6-deoxysucrose ([18F]FDS) analogs. Each [18F]FDS derivative was independently introduced into wild-type or sut1 mutant plants, which are defective in sucrose phloem loading. All three (1'-, 6'-, and 6-) [18F]FDS derivatives were efficiently and equally translocated, similarly to carbon-14 [14C]-labeled sucrose. Hence, individually replacing the hydroxyl groups at these positions within sucrose does not interfere with substrate recognition, binding, or membrane transport processes, and hydroxyl groups at these three positions are not essential for hydrogen bonding between sucrose and ZmSUT1. [18F]FDS imaging afforded several advantages compared to [14C]-sucrose detection. We calculated that 1'-[18F]FDS was transported at approximately a rate of 0.90 ± 0.15 m.h-1 in wild-type leaves, and at 0.68 ± 0.25 m.h-1 in sut1 mutant leaves. Collectively, our data indicated that [18F]FDS analogs are valuable tools to probe sucrose-SUT interactions and to monitor sucrose transport in plants.
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Affiliation(s)
- Thu M Tran
- Plant Imaging Consortium, United States; Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri, Columbia, MO 65211, United States
| | - Carissa S Hampton
- Department of Chemistry, University of Missouri, Columbia, MO 65211, United States; University of Missouri Research Reactor, University of Missouri, Columbia, MO 65211, United States
| | - Tom W Brossard
- Department of Chemistry, University of Missouri, Columbia, MO 65211, United States; University of Missouri Research Reactor, University of Missouri, Columbia, MO 65211, United States
| | - Michael Harmata
- Department of Chemistry, University of Missouri, Columbia, MO 65211, United States
| | - J David Robertson
- Department of Chemistry, University of Missouri, Columbia, MO 65211, United States; University of Missouri Research Reactor, University of Missouri, Columbia, MO 65211, United States
| | - Silvia S Jurisson
- Plant Imaging Consortium, United States; Department of Chemistry, University of Missouri, Columbia, MO 65211, United States
| | - David M Braun
- Plant Imaging Consortium, United States; Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri, Columbia, MO 65211, United States.
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14
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Baker RF, Leach KA, Boyer NR, Swyers MJ, Benitez-Alfonso Y, Skopelitis T, Luo A, Sylvester A, Jackson D, Braun DM. Sucrose Transporter ZmSut1 Expression and Localization Uncover New Insights into Sucrose Phloem Loading. PLANT PHYSIOLOGY 2016; 172:1876-1898. [PMID: 27621426 PMCID: PMC5100798 DOI: 10.1104/pp.16.00884] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Accepted: 09/08/2016] [Indexed: 05/18/2023]
Abstract
Sucrose transporters (SUTs) translocate sucrose (Suc) across cellular membranes, and in eudicots, multiple SUTs are known to function in Suc phloem loading in leaves. In maize (Zea mays), the Sucrose Transporter1 (ZmSut1) gene has been implicated in Suc phloem loading based upon RNA expression in leaves, electrophysiological experiments, and phenotypic analysis of zmsut1 mutant plants. However, no previous studies have examined the cellular expression of ZmSut1 RNA or the subcellular localization of the ZmSUT1 protein to assess the gene's hypothesized function in Suc phloem loading or to evaluate its potential roles, such as phloem unloading, in nonphotosynthetic tissues. To this end, we performed RNA in situ hybridization experiments, promoter-reporter gene analyses, and ZmSUT1 localization studies to elucidate the cellular expression pattern of the ZmSut1 transcript and protein. These data showed that ZmSut1 was expressed in multiple cell types throughout the plant and indicated that it functions in phloem companion cells to load Suc and also in other cell types to retrieve Suc from the apoplasm to prevent its accumulation and loss to the transpiration stream. Additionally, by comparing a phloem-mobile tracer with ZmSut1 expression, we determined that developing maize leaves dynamically switch from symplasmic to apoplasmic phloem unloading, reconciling previously conflicting reports, and suggest that ZmSut1 does not have an apparent function in either unloading process. A model for the dual roles for ZmSut1 function (phloem loading and apoplasmic recycling), Sut1 evolution, and its possible use to enhance Suc export from leaves in engineering C3 grasses for C4 photosynthesis is discussed.
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Affiliation(s)
- R Frank Baker
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.)
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.)
| | - Kristen A Leach
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.)
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.)
| | - Nathanial R Boyer
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.)
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.)
| | - Michael J Swyers
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.)
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.)
| | - Yoselin Benitez-Alfonso
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.)
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.)
| | - Tara Skopelitis
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.)
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.)
| | - Anding Luo
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.)
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.)
| | - Anne Sylvester
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.)
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.)
| | - David Jackson
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.)
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.)
| | - David M Braun
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.);
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.)
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15
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Griffiths CA, Paul MJ, Foyer CH. Metabolite transport and associated sugar signalling systems underpinning source/sink interactions. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1857:1715-25. [PMID: 27487250 PMCID: PMC5001786 DOI: 10.1016/j.bbabio.2016.07.007] [Citation(s) in RCA: 94] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Revised: 06/06/2016] [Accepted: 07/23/2016] [Indexed: 11/19/2022]
Abstract
Metabolite transport between organelles, cells and source and sink tissues not only enables pathway co-ordination but it also facilitates whole plant communication, particularly in the transmission of information concerning resource availability. Carbon assimilation is co-ordinated with nitrogen assimilation to ensure that the building blocks of biomass production, amino acids and carbon skeletons, are available at the required amounts and stoichiometry, with associated transport processes making certain that these essential resources are transported from their sites of synthesis to those of utilisation. Of the many possible posttranslational mechanisms that might participate in efficient co-ordination of metabolism and transport only reversible thiol-disulphide exchange mechanisms have been described in detail. Sucrose and trehalose metabolism are intertwined in the signalling hub that ensures appropriate resource allocation to drive growth and development under optimal and stress conditions, with trehalose-6-phosphate acting as an important signal for sucrose availability. The formidable suite of plant metabolite transporters provides enormous flexibility and adaptability in inter-pathway coordination and source-sink interactions. Focussing on the carbon metabolism network, we highlight the functions of different transporter families, and the important of thioredoxins in the metabolic dialogue between source and sink tissues. In addition, we address how these systems can be tailored for crop improvement.
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Affiliation(s)
- Cara A Griffiths
- Plant Biology and Crop Science, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK
| | - Matthew J Paul
- Plant Biology and Crop Science, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK
| | - Christine H Foyer
- Centre for Plant Sciences, School of Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK.
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16
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Leach KA, Braun DM. Soluble Sugar and Starch Extraction and Quantification from Maize (
Zea mays
) Leaves. ACTA ACUST UNITED AC 2016; 1:139-161. [DOI: 10.1002/cppb.20018] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Kristen A. Leach
- Division of Biological Sciences, Interdisciplinary Plant Group, Missouri Maize Center, University of Missouri Columbia Missouri
| | - David M. Braun
- Division of Biological Sciences, Interdisciplinary Plant Group, Missouri Maize Center, University of Missouri Columbia Missouri
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17
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Bihmidine S, Baker RF, Hoffner C, Braun DM. Sucrose accumulation in sweet sorghum stems occurs by apoplasmic phloem unloading and does not involve differential Sucrose transporter expression. BMC PLANT BIOLOGY 2015; 15:186. [PMID: 26223524 PMCID: PMC4518677 DOI: 10.1186/s12870-015-0572-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Accepted: 07/16/2015] [Indexed: 05/19/2023]
Abstract
BACKGROUND Sorghum (Sorghum bicolor L. Moench) cultivars store non-structural carbohydrates predominantly as either starch in seeds (grain sorghums) or sugars in stems (sweet sorghums). Previous research determined that sucrose accumulation in sweet sorghum stems was not correlated with the activities of enzymes functioning in sucrose metabolism, and that an apoplasmic transport step may be involved in stem sucrose accumulation. However, the sucrose unloading pathway from stem phloem to storage parenchyma cells remains unelucidated. Sucrose transporters (SUTs) transport sucrose across membranes, and have been proposed to function in sucrose partitioning differences between sweet and grain sorghums. The purpose of this study was to characterize the key differences in carbohydrate accumulation between a sweet and a grain sorghum, to define the path sucrose may follow for accumulation in sorghum stems, and to determine the roles played by sorghum SUTs in stem sucrose accumulation. RESULTS Dye tracer studies to determine the sucrose transport route revealed that, for both the sweet sorghum cultivar Wray and grain sorghum cultivar Macia, the phloem in the stem veins was symplasmically isolated from surrounding cells, suggesting sucrose was apoplasmically unloaded. Once in the phloem apoplasm, a soluble tracer diffused from the vein to stem parenchyma cell walls, indicating the lignified mestome sheath encompassing the vein did not prevent apoplasmic flux outside of the vein. To characterize carbohydrate partitioning differences between Wray and Macia, we compared the growth, stem juice volume, solute contents, SbSUTs gene expression, and additional traits. Contrary to previous findings, we detected no significant differences in SbSUTs gene expression within stem tissues. CONCLUSIONS Phloem sieve tubes within sweet and grain sorghum stems are symplasmically isolated from surrounding cells; hence, unloading from the phloem likely occurs apoplasmically, thereby defining the location of the previously postulated step for sucrose transport. Additionally, no changes in SbSUTs gene expression were detected in sweet vs. grain sorghum stems, suggesting alterations in SbSUT transcript levels do not account for the carbohydrate partitioning differences between cultivars. A model illustrating sucrose phloem unloading and movement to stem storage parenchyma, and highlighting roles for sucrose transport proteins in sorghum stems is discussed.
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Affiliation(s)
- Saadia Bihmidine
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri, 110 Tucker Hall, Columbia, MO, 65211, USA.
| | - R Frank Baker
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri, 110 Tucker Hall, Columbia, MO, 65211, USA.
- University of Missouri Molecular Cytology Core, 120 Bond Life Sciences Center, 1201 Rollins Street, Columbia, MO, 65211-7310, USA.
| | - Cassandra Hoffner
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri, 110 Tucker Hall, Columbia, MO, 65211, USA.
- Sigma-Aldrich Biotech, 545 S. Ewing, Saint Louis, MO, 63103, USA.
| | - David M Braun
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri, 110 Tucker Hall, Columbia, MO, 65211, USA.
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18
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Wu J, Zhang Z, Zhang Q, Han X, Gu X, Lu T. The molecular cloning and clarification of a photorespiratory mutant, oscdm1, using enhancer trapping. Front Genet 2015; 6:226. [PMID: 26191072 PMCID: PMC4490251 DOI: 10.3389/fgene.2015.00226] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Accepted: 06/15/2015] [Indexed: 01/08/2023] Open
Abstract
Enhancer trap systems have been demonstrated to increase the effectiveness of gene identification in rice. In this study, a chlorophyll-deficient mutant, named oscdm1, was screened and characterized in detail from a T-DNA enhancer-tagged population. The oscdm1 plants were different from other chlorophyll-deficient mutants; they produced chlorotic leaves at the third leaf stage, which gradually died with further growth of the plants. However, the oscdm1 plants were able to survive exposure to elevated CO2 levels, similar to photorespiratory mutants. An analysis of the T-DNA flanking sequence in the oscdm1 plants showed that the T-DNA was inserted into the promoter region of a serine hydroxymethyltransferase (SHMT) gene. OsSHMT1 is a key enzyme that is ubiquitous in nature and structurally conserved across kingdoms. The enzyme is responsible for the interconversion of serine and glycine and is essential for cellular one-carbon metabolism. Full-length OsSHMT1 complemented the oscdm1 phenotype, and the downregulation of OsSHMT1 in wild-type plants by RNA interference (RNAi) produced plants that mimicked the oscdm1 phenotype. GUS assays and quantitative PCR revealed the preferential expression of OsSHMT1 in young leaves. TEM revealed serious damage to the thylakoid membrane in oscdm1 chloroplasts. The oscdm1 plants showed more extensive damage than wild type using an IMAGING-PAM fluorometer, especially under high light intensities. OsSHMT1-GFP localized exclusively to mitochondria. Further analysis revealed that the H2O2 content in the oscdm1 plants was twice that in wild type at the fourth leaf stage. This suggests that the thylakoid membrane damage observed in the oscdm1 plants was caused by excessive H2O2. Interestingly, OsSHMT1-overexpressing plants exhibited increased photosynthetic efficiency and improved plant productivity. These results lay the foundation for further study of the OsSHMT1 gene and will help illuminate the functional role of OsSHMT1 in photorespiration in rice.
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Affiliation(s)
- Jinxia Wu
- Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences Beijing, China
| | - Zhiguo Zhang
- Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences Beijing, China
| | - Qian Zhang
- Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences Beijing, China
| | - Xiao Han
- Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences Beijing, China
| | - Xiaofeng Gu
- Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences Beijing, China
| | - Tiegang Lu
- Biotechnology Research Institute/National Key Facility for Genetic Resources and Gene Improvement, The Chinese Academy of Agricultural Sciences Beijing, China
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Rotsch D, Brossard T, Bihmidine S, Ying W, Gaddam V, Harmata M, Robertson JD, Swyers M, Jurisson SS, Braun DM. Radiosynthesis of 6'-Deoxy-6'[18F]Fluorosucrose via Automated Synthesis and Its Utility to Study In Vivo Sucrose Transport in Maize (Zea mays) Leaves. PLoS One 2015; 10:e0128989. [PMID: 26024520 PMCID: PMC4449027 DOI: 10.1371/journal.pone.0128989] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2015] [Accepted: 05/01/2015] [Indexed: 01/08/2023] Open
Abstract
Sugars produced from photosynthesis in leaves are transported through the phloem tissues within veins and delivered to non-photosynthetic organs, such as roots, stems, flowers, and seeds, to support their growth and/or storage of carbohydrates. However, because the phloem is located internally within the veins, it is difficult to access and to study the dynamics of sugar transport. Radioactive tracers have been extensively used to study vascular transport in plants and have provided great insights into transport dynamics. To better study sucrose partitioning in vivo, a novel radioactive analog of sucrose was synthesized through a completely chemical synthesis route by substituting fluorine-18 (half-life 110 min) at the 6' position to generate 6'-deoxy-6'[(18)F]fluorosucrose ((18)FS). This radiotracer was then used to compare sucrose transport between wild-type maize plants and mutant plants lacking the Sucrose transporter1 (Sut1) gene, which has been shown to function in sucrose phloem loading. Our results demonstrate that (18)FS is transported in vivo, with the wild-type plants showing a greater rate of transport down the leaf blade than the sut1 mutant plants. A similar transport pattern was also observed for universally labeled [U-(14)C]sucrose ([U-(14)C]suc). Our findings support the proposed sucrose phloem loading function of the Sut1 gene in maize, and additionally demonstrate that the (18)FS analog is a valuable, new tool that offers imaging advantages over [U-(14)C]suc for studying phloem transport in plants.
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Affiliation(s)
- David Rotsch
- Department of Chemistry, University of Missouri, Columbia, Missouri, United States of America
| | - Tom Brossard
- Department of Chemistry, University of Missouri, Columbia, Missouri, United States of America
| | - Saadia Bihmidine
- Division of Biological Sciences, Interdisciplinary Plant Group and the Missouri Maize Center, University of Missouri, Columbia, Missouri, United States of America
| | - Weijiang Ying
- Department of Chemistry, University of Missouri, Columbia, Missouri, United States of America
| | - Vikram Gaddam
- Department of Chemistry, University of Missouri, Columbia, Missouri, United States of America
| | - Michael Harmata
- Department of Chemistry, University of Missouri, Columbia, Missouri, United States of America
| | - J. David Robertson
- Department of Chemistry, University of Missouri, Columbia, Missouri, United States of America
- University of Missouri Research Reactor, University of Missouri, Columbia, Missouri, United States of America
| | - Michael Swyers
- Division of Biological Sciences, Interdisciplinary Plant Group and the Missouri Maize Center, University of Missouri, Columbia, Missouri, United States of America
| | - Silvia S. Jurisson
- Department of Chemistry, University of Missouri, Columbia, Missouri, United States of America
| | - David M. Braun
- Division of Biological Sciences, Interdisciplinary Plant Group and the Missouri Maize Center, University of Missouri, Columbia, Missouri, United States of America
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Braun DM, Wang L, Ruan YL. Understanding and manipulating sucrose phloem loading, unloading, metabolism, and signalling to enhance crop yield and food security. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:1713-35. [PMID: 24347463 DOI: 10.1093/jxb/ert416] [Citation(s) in RCA: 227] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Sucrose is produced in, and translocated from, photosynthetically active leaves (sources) to support non-photosynthetic tissues (sinks), such as developing seeds, fruits, and tubers. Different plants can utilize distinct mechanisms to transport sucrose into the phloem sieve tubes in source leaves. While phloem loading mechanisms have been extensively studied in dicot plants, there is less information about phloem loading in monocots. Maize and rice are major dietary staples, which have previously been proposed to use different cellular routes to transport sucrose from photosynthetic cells into the translocation stream. The anatomical, physiological, and genetic evidence supporting these conflicting hypotheses is examined. Upon entering sink cells, sucrose often is degraded into hexoses for a wide range of metabolic and storage processes, including biosynthesis of starch, protein, and cellulose, which are all major constituents for food, fibre, and fuel. Sucrose, glucose, fructose, and their derivate, trehalose-6-phosphate, also serve as signalling molecules to regulate gene expression either directly or through cross-talk with other signalling pathways. As such, sugar transport and metabolism play pivotal roles in plant development and realization of crop yield that needs to be increased substantially to meet the projected population demand in the foreseeable future. This review will discuss the current understanding of the control of carbon partitioning from the cellular to whole-plant levels, focusing on (i) the pathways employed for phloem loading in source leaves, particularly in grasses, and the routes used in sink organs for phloem unloading; (ii) the transporter proteins responsible for sugar efflux and influx across plasma membranes; and (iii) the key enzymes regulating sucrose metabolism, signalling, and utilization. Examples of how sugar transport and metabolism can be manipulated to improve crop productivity and stress tolerance are discussed.
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Affiliation(s)
- David M Braun
- Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri, Columbia, MO 65211, USA
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Petti C, Harman-Ware AE, Tateno M, Kushwaha R, Shearer A, Downie AB, Crocker M, DeBolt S. Sorghum mutant RG displays antithetic leaf shoot lignin accumulation resulting in improved stem saccharification properties. BIOTECHNOLOGY FOR BIOFUELS 2013; 6:146. [PMID: 24103129 PMCID: PMC3852544 DOI: 10.1186/1754-6834-6-146] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Accepted: 09/24/2013] [Indexed: 05/06/2023]
Abstract
BACKGROUND Improving saccharification efficiency in bioenergy crop species remains an important challenge. Here, we report the characterization of a Sorghum (Sorghum bicolor L.) mutant, named REDforGREEN (RG), as a bioenergy feedstock. RESULTS It was found that RG displayed increased accumulation of lignin in leaves and depletion in the stems, antithetic to the trend observed in wild type. Consistent with these measurements, the RG leaf tissue displayed reduced saccharification efficiency whereas the stem saccharification efficiency increased relative to wild type. Reduced lignin was linked to improved saccharification in RG stems, but a chemical shift to greater S:G ratios in RG stem lignin was also observed. Similarities in cellulose content and structure by XRD-analysis support the correlation between increased saccharification properties and reduced lignin instead of changes in the cellulose composition and/or structure. CONCLUSION Antithetic lignin accumulation was observed in the RG mutant leaf-and stem-tissue, which resulted in greater saccharification efficiency in the RG stem and differential thermochemical product yield in high lignin leaves. Thus, the red leaf coloration of the RG mutant represents a potential marker for improved conversion of stem cellulose to fermentable sugars in the C4 grass Sorghum.
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Affiliation(s)
- Carloalberto Petti
- Plant Physiology, Department of Horticulture, Agricultural Science Center North, University of Kentucky, Lexington, KY 40546, USA
| | - Anne E Harman-Ware
- Center for Applied Energy Research, University of Kentucky, 2540 Research Park Drive, Lexington, KY 40511, USA
| | - Mizuki Tateno
- Plant Physiology, Department of Horticulture, Agricultural Science Center North, University of Kentucky, Lexington, KY 40546, USA
| | - Rekha Kushwaha
- Plant Physiology, Department of Horticulture, Agricultural Science Center North, University of Kentucky, Lexington, KY 40546, USA
| | - Andrew Shearer
- Plant Physiology, Department of Horticulture, Agricultural Science Center North, University of Kentucky, Lexington, KY 40546, USA
| | - A Bruce Downie
- Plant Physiology, Department of Horticulture, Agricultural Science Center North, University of Kentucky, Lexington, KY 40546, USA
| | - Mark Crocker
- Center for Applied Energy Research, University of Kentucky, 2540 Research Park Drive, Lexington, KY 40511, USA
| | - Seth DeBolt
- Plant Physiology, Department of Horticulture, Agricultural Science Center North, University of Kentucky, Lexington, KY 40546, USA
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Bihmidine S, Hunter CT, Johns CE, Koch KE, Braun DM. Regulation of assimilate import into sink organs: update on molecular drivers of sink strength. FRONTIERS IN PLANT SCIENCE 2013; 4:177. [PMID: 23761804 PMCID: PMC3671192 DOI: 10.3389/fpls.2013.00177] [Citation(s) in RCA: 139] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Accepted: 05/17/2013] [Indexed: 05/18/2023]
Abstract
Recent developments have altered our view of molecular mechanisms that determine sink strength, defined here as the capacity of non-photosynthetic structures to compete for import of photoassimilates. We review new findings from diverse systems, including stems, seeds, flowers, and fruits. An important advance has been the identification of new transporters and facilitators with major roles in the accumulation and equilibration of sugars at a cellular level. Exactly where each exerts its effect varies among systems. Sugarcane and sweet sorghum stems, for example, both accumulate high levels of sucrose, but may do so via different paths. The distinction is central to strategies for targeted manipulation of sink strength using transporter genes, and shows the importance of system-specific analyses. Another major advance has been the identification of deep hypoxia as a feature of normal grain development. This means that molecular drivers of sink strength in endosperm operate in very low oxygen levels, and under metabolic conditions quite different than previously assumed. Successful enhancement of sink strength has nonetheless been achieved in grains by up-regulating genes for starch biosynthesis. Additionally, our understanding of sink strength is enhanced by awareness of the dual roles played by invertases (INVs), not only in sucrose metabolism, but also in production of the hexose sugar signals that regulate cell cycle and cell division programs. These contributions of INV to cell expansion and division prove to be vital for establishment of young sinks ranging from flowers to fruit. Since INV genes are themselves sugar-responsive "feast genes," they can mediate a feed-forward enhancement of sink strength when assimilates are abundant. Greater overall productivity and yield have thus been attained in key instances, indicating that even broader enhancements may be achievable as we discover the detailed molecular mechanisms that drive sink strength in diverse systems.
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Affiliation(s)
- Saadia Bihmidine
- Division of Biological Sciences, University of MissouriColumbia, MO, USA
- Interdisciplinary Plant Group, University of MissouriColumbia, MO, USA
- Missouri Maize Center, University of MissouriColumbia, MO, USA
| | - Charles T. Hunter
- Horticultural Sciences Department, University of FloridaGainesville, FL, USA
- Plant Molecular and Cellular Biology Program, University of FloridaGainesville, FL, USA
| | - Christine E. Johns
- Horticultural Sciences Department, University of FloridaGainesville, FL, USA
- Plant Molecular and Cellular Biology Program, University of FloridaGainesville, FL, USA
| | - Karen E. Koch
- Horticultural Sciences Department, University of FloridaGainesville, FL, USA
- Plant Molecular and Cellular Biology Program, University of FloridaGainesville, FL, USA
| | - David M. Braun
- Division of Biological Sciences, University of MissouriColumbia, MO, USA
- Interdisciplinary Plant Group, University of MissouriColumbia, MO, USA
- Missouri Maize Center, University of MissouriColumbia, MO, USA
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Baker RF, Slewinski TL, Braun DM. The tie-dyed pathway promotes symplastic trafficking in the phloem. PLANT SIGNALING & BEHAVIOR 2013; 8:e24540. [PMID: 23603956 PMCID: PMC3909061 DOI: 10.4161/psb.24540] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Revised: 04/02/2013] [Accepted: 04/03/2013] [Indexed: 05/18/2023]
Abstract
The tie-dyed1 (tdy1) and tdy2 mutants of maize exhibit leaf regions with starch hyperaccumulation and display unusual genetic interactions, suggesting they function in the same physiological process. Tdy2 encodes a putative callose synthase and is expressed in developing vascular tissues of immature leaves. Radiolabelling experiments and transmission electron microscopy (TEM) revealed symplastic trafficking within the phloem was perturbed at the companion cell/sieve element interface. Here, we show that as reported for tdy2 mutants, tdy1 yellow leaf regions display an excessive oil-droplet phenotype in the companion cells. Based on the proposed function of Tdy2 as a callose synthase, our previous work characterizing Tdy1 as a novel, transmembrane-localized protein, and the present findings, we speculate how TDY1 and TDY2 might interact to promote symplastic transport of both solutes and developmentally instructive macromolecules during vascular development at the companion cell/sieve element interface.
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Affiliation(s)
- R. Frank Baker
- Division of Biological Sciences and Interdisciplinary Plant Group; Missouri Maize Center; University of Missouri; Columbia, MO USA
| | | | - David M. Braun
- Division of Biological Sciences and Interdisciplinary Plant Group; Missouri Maize Center; University of Missouri; Columbia, MO USA
- Correspondence to: David M. Braun,
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Vilaine F, Kerchev P, Clément G, Batailler B, Cayla T, Bill L, Gissot L, Dinant S. Increased expression of a phloem membrane protein encoded by NHL26 alters phloem export and sugar partitioning in Arabidopsis. THE PLANT CELL 2013; 25:1689-708. [PMID: 23715470 PMCID: PMC3694700 DOI: 10.1105/tpc.113.111849] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2013] [Revised: 04/30/2013] [Accepted: 05/13/2013] [Indexed: 05/18/2023]
Abstract
The complex process of phloem sugar transport involves symplasmic and apoplasmic events. We characterized Arabidopsis thaliana lines ectopically expressing a phloem-specific gene encoding NDR1/HIN1-like26 (NHL26), a putative membrane protein. NHL26 overexpressor plants grew more slowly than wild-type plants, accumulated high levels of carbohydrates in mature leaves, and had a higher shoot biomass, contrasting with slower root growth and a lower seed yield. Similar effects were observed when NHL26 was overexpressed in companion cells, under the control of a companion cell-specific promoter. The soluble sugar content of the phloem sap and sink organs was lower than that in the wild type, providing evidence of a sugar export defect. This was confirmed in a phloem-export assay with the symplastic tracer carboxyfluorescein diacetate. Leaf sugar accumulation was accompanied by higher organic acid, amino acid, and protein contents, whereas analysis of the metabolite profile of phloem sap exudate revealed no change in amino acid or organic acid content, indicating a specific effect on sugar export. NHL26 was found to be located in the phloem plasmodesmata and the endoplasmic reticulum. These findings reveal that NHL26 accumulation affects either the permeability of plasmodesmata or sugar signaling in companion cells, with a specific effect on sugar export.
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Affiliation(s)
- Françoise Vilaine
- Unité Mixte de Recherche 1318, Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique–AgroParisTech, F-78000 Versailles, France
| | - Pavel Kerchev
- Unité Mixte de Recherche 1318, Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique–AgroParisTech, F-78000 Versailles, France
| | - Gilles Clément
- Unité Mixte de Recherche 1318, Plateforme de Chimie du Végétal, Institut National de la Recherche Agronomique, F-78000 Versailles, France
| | - Brigitte Batailler
- Unité Mixte de Recherche 1332, Biologie du Fruit et Pathologie, Institut National de la Recherche Agronomique, F-33140 Villenave d’Ornon, France
- Université de Bordeaux, Centre National de la Recherche Scientifique, Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Service 3420, Bordeaux Imaging Center, F-33000 Bordeaux, France
| | - Thibaud Cayla
- Unité Mixte de Recherche 1318, Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique–AgroParisTech, F-78000 Versailles, France
| | - Laurence Bill
- Unité Mixte de Recherche 1318, Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique–AgroParisTech, F-78000 Versailles, France
| | - Lionel Gissot
- Unité Mixte de Recherche 1318, Plateforme de Cytologie et Imagerie Végétale, Institut National de la Recherche Agronomique, F-78000 Versailles, France
| | - Sylvie Dinant
- Unité Mixte de Recherche 1318, Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique–AgroParisTech, F-78000 Versailles, France
- Address correspondence to
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25
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Slewinski TL, Baker RF, Stubert A, Braun DM. Tie-dyed2 encodes a callose synthase that functions in vein development and affects symplastic trafficking within the phloem of maize leaves. PLANT PHYSIOLOGY 2012; 160:1540-50. [PMID: 22932757 PMCID: PMC3490577 DOI: 10.1104/pp.112.202473] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2012] [Accepted: 08/28/2012] [Indexed: 05/18/2023]
Abstract
The tie-dyed2 (tdy2) mutant of maize (Zea mays) displays variegated green and yellow leaves. Intriguingly, the yellow leaf tissues hyperaccumulate starch and sucrose, the soluble sugar transported long distance through the phloem of veins. To determine the molecular basis for Tdy2 function, we cloned the gene and found that Tdy2 encodes a callose synthase. RNA in situ hybridizations revealed that in developing leaves, Tdy2 was most highly expressed in the vascular tissue. Comparative expression analysis with the vascular marker maize PINFORMED1a-yellow fluorescent protein confirmed that Tdy2 was expressed in developing vein tissues. To ascertain whether the defect in tdy2 leaves affected the movement of sucrose into the phloem or its long-distance transport, we performed radiolabeled and fluorescent dye tracer assays. The results showed that tdy2 yellow leaf regions were defective in phloem export but competent in long-distance transport. Furthermore, transmission electron microscopy of tdy2 yellow leaf regions showed incomplete vascular differentiation and implicated a defect in cell-to-cell solute movement between phloem companion cells and sieve elements. The disruption of sucrose movement in the phloem in tdy2 mutants provides evidence that the Tdy2 callose synthase functions in vascular maturation and that the vascular defects result in impaired symplastic trafficking into the phloem translocation stream.
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26
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Koh EJ, Zhou L, Williams DS, Park J, Ding N, Duan YP, Kang BH. Callose deposition in the phloem plasmodesmata and inhibition of phloem transport in citrus leaves infected with "Candidatus Liberibacter asiaticus". PROTOPLASMA 2012; 249:687-97. [PMID: 21874517 DOI: 10.1007/s00709-011-0312-3] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2011] [Accepted: 06/17/2011] [Indexed: 05/22/2023]
Abstract
Huanglongbing (HLB) is a destructive disease of citrus trees caused by phloem-limited bacteria, Candidatus Liberibacter spp. One of the early microscopic manifestations of HLB is excessive starch accumulation in leaf chloroplasts. We hypothesize that the causative bacteria in the phloem may intervene photoassimilate export, causing the starch to over-accumulate. We examined citrus leaf phloem cells by microscopy methods to characterize plant responses to Liberibacter infection and the contribution of these responses to the pathogenicity of HLB. Plasmodesmata pore units (PPUs) connecting companion cells and sieve elements were stained with a callose-specific dye in the Liberibacter-infected leaf phloem cells; callose accumulated around PPUs before starch began to accumulate in the chloroplasts. When examined by transmission electron microscopy, PPUs with abnormally large callose deposits were more abundant in the Liberibacter-infected samples than in the uninfected samples. We demonstrated an impairment of symplastic dye movement into the vascular tissue and delayed photoassimilate export in the Liberibacter-infected leaves. Liberibacter infection was also linked to callose deposition in the sieve plates, which effectively reduced the sizes of sieve pores. Our results indicate that Liberibacter infection is accompanied by callose deposition in PPUs and sieve pores of the sieve tubes and suggest that the phloem plugging by callose inhibits phloem transport, contributing to the development of HLB symptoms.
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Affiliation(s)
- Eun-Ji Koh
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611, USA
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Depège-Fargeix N, Javelle M, Chambrier P, Frangne N, Gerentes D, Perez P, Rogowsky PM, Vernoud V. Functional characterization of the HD-ZIP IV transcription factor OCL1 from maize. JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:293-305. [PMID: 20819789 DOI: 10.1093/jxb/erq267] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
OCL1 (OUTER CELL LAYER1) encodes a maize HD-ZIP class IV transcription factor (TF) characterized by the presence of a homeo DNA-binding domain (HD), a dimerization leucine zipper domain (ZIP), and a steroidogenic acute regulatory protein (StAR)-related lipid transfer domain (START) involved in lipid transport in animals but the function of which is still unknown in plants. By combining yeast and plant trans-activation assays, the transcriptional activation domain of OCL1 was localized to 85 amino acids in the N-terminal part of the START domain. Full-length OCL1 devoid of this activation domain is unable to trans-activate a reporter gene under the control of a minimal promoter fused to six repeats of the L1 box, a cis-element present in target genes of HD-ZIP IV TFs in Arabidopsis. In addition, ectopic expression of OCL1 leads to pleiotropic phenotypic aberrations in transgenic maize plants, the most conspicuous one being a strong delay in flowering time which is correlated with the misexpression of molecular markers for floral transition such as ZMM4 (Zea Mays MADS-box4) or DLF1 (DELAYED FLOWERING1). As suggested by the interaction in planta between OCL1 and SWI3C1, a bona fide subunit of the SWI/SNF complex, OCL1 may modulate transcriptional activity of its target genes by interaction with a chromatin remodelling complex.
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Affiliation(s)
- Nathalie Depège-Fargeix
- Université de Lyon, Ecole Normale Supérieure de Lyon, Université Lyon 1, IFR128 BioSciences Lyon Gerland, Unité Reproduction et Développement des Plantes, F-69364 Lyon, France
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Slewinski TL, Garg A, Johal GS, Braun DM. Maize SUT1 functions in phloem loading. PLANT SIGNALING & BEHAVIOR 2010; 5:687-90. [PMID: 20404497 PMCID: PMC3001560 DOI: 10.4161/psb.5.6.11575] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2010] [Accepted: 02/16/2010] [Indexed: 05/18/2023]
Abstract
The functions of dicot sucrose transporters (SUTs) in apoplastic phloem loading of sucrose are well established; however, whether SUTs similarly function in monocots was unresolved. To address this question, we recently provided genetic evidence that ZmSUT1 from maize (Zea mays) is required for efficient phloem loading. sut1-m1 mutant plants hyperaccumulate carbohydrates in leaves, are defective in loading sucrose into the phloem, and have altered biomass partitioning. Presumably due to the hyperaccumulation of soluble sugars in leaves, mutations in ZmSUT1 lead to downregulation of chlorophyll accumulation, photosynthesis and stomatal conductance. However, because we had identified only a single mutant allele, we were not able to exclude the possibility that the mutant phenotypes were instead caused by a closely linked mutation. Based on a novel aspect of the sut1 mutant phenotype, secretion of a concentrated sugar solution from leaf hydathodes, we identified an additional mutant allele, sut1-m4. This confirms that the mutation of SUT1 is responsible for the impairment in phloem loading. In addition, the sut1-m4 mutant does not accumulate transcripts, supporting the findings reported previously that the original mutant allele is also a null mutation. Collectively, these data demonstrate that ZmSUT1 functions to phloem load sucrose in maize leaves.
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Affiliation(s)
- Thomas L Slewinski
- Department of Biology, Pennsylvania State University, University Park, PA, USA
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30
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Slewinski TL, Braun DM. The psychedelic genes of maize redundantly promote carbohydrate export from leaves. Genetics 2010; 185:221-32. [PMID: 20142436 PMCID: PMC2870957 DOI: 10.1534/genetics.109.113357] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2009] [Accepted: 02/06/2010] [Indexed: 11/18/2022] Open
Abstract
Whole-plant carbohydrate partitioning involves the assimilation of carbon in leaves and its translocation to nonphotosynthetic tissues. This process is fundamental to plant growth and development, but its regulation is poorly understood. To identify genes controlling carbohydrate partitioning, we isolated mutants that are defective in exporting fixed carbon from leaves. Here we describe psychedelic (psc), a new mutant of maize (Zea mays) that is perturbed in carbohydrate partitioning. psc mutants exhibit stable, discrete chlorotic and green regions within their leaves. psc chlorotic tissues hyperaccumulate starch and soluble sugars, while psc green tissues appear comparable to wild-type leaves. The psc chlorotic and green tissue boundaries are usually delineated by larger veins, suggesting that translocation of a mobile compound through the veins may influence the tissue phenotype. psc mutants display altered biomass partitioning, which is consistent with reduced carbohydrate export from leaves to developing tissues. We determined that the psc mutation is unlinked to previously characterized maize leaf carbohydrate hyperaccumulation mutants. Additionally, we found that the psc mutant phenotype is inherited as a recessive, duplicate-factor trait in some inbred lines. Genetic analyses with other maize mutants with variegated leaves and impaired carbohydrate partitioning suggest that Psc defines an independent pathway. Therefore, investigations into the psc mutation have uncovered two previously unknown genes that redundantly function to regulate carbohydrate partitioning in maize.
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Affiliation(s)
| | - David M. Braun
- Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802
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31
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Huang M, Slewinski TL, Baker RF, Janick-Buckner D, Buckner B, Johal GS, Braun DM. Camouflage patterning in maize leaves results from a defect in porphobilinogen deaminase. MOLECULAR PLANT 2009; 2:773-789. [PMID: 19825655 DOI: 10.1093/mp/ssp029] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Maize leaves are produced from polarized cell divisions that result in clonal cell lineages arrayed along the long axis of the leaf. We utilized this stereotypical division pattern to identify a collection of mutants that form chloroplast pigmentation sectors that violate the clonal cell lineages. Here, we describe the camouflage1 (cf1) mutant, which develops nonclonal, yellow-green sectors in its leaves. We cloned the cf1 gene by transposon tagging and determined that it encodes porphobilinogen deaminase (PBGD), an enzyme that functions early in chlorophyll and heme biosynthesis. While PBGD has been characterized biochemically, no viable mutations in this gene have been reported in plants. To investigate the in vivo function of PBGD, we characterized the cf1 mutant. Histological analyses revealed that cf1 yellow sectors display the novel phenotype of bundle sheath cell-specific death. Light-shift experiments determined that constant light suppressed cf1 sector formation, a dark/light transition is required to induce yellow sectors, and that sectors form only during a limited time of leaf development. Biochemical experiments determined that cf1 mutant leaves have decreased PBGD activity and increased levels of the enzyme substrate in both green and yellow regions. Furthermore, the cf1 yellow regions displayed a reduction in catalase activity. A threshold model is hypothesized to explain the cf1 variegation and incorporates photosynthetic cell differentiation, reactive oxygen species scavenging, and PBGD function.
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Affiliation(s)
- Mingshu Huang
- Department of Biology, Pennsylvania State University, University Park, PA 16802
| | - Thomas L Slewinski
- Department of Biology, Pennsylvania State University, University Park, PA 16802
| | - R Frank Baker
- Department of Biology, Pennsylvania State University, University Park, PA 16802
| | | | - Brent Buckner
- Division of Science, Truman State University, Kirksville, MO 63501
| | - Gurmukh S Johal
- Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907
| | - David M Braun
- Department of Biology, Pennsylvania State University, University Park, PA 16802.
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Slewinski TL, Meeley R, Braun DM. Sucrose transporter1 functions in phloem loading in maize leaves. JOURNAL OF EXPERIMENTAL BOTANY 2009; 60:881-92. [PMID: 19181865 PMCID: PMC2652052 DOI: 10.1093/jxb/ern335] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2008] [Revised: 11/26/2008] [Accepted: 11/27/2008] [Indexed: 05/18/2023]
Abstract
In most plants, sucrose is exported from source leaves to carbon-importing sink tissues to sustain their growth and metabolism. Apoplastic phloem-loading species require sucrose transporters (SUTs) to transport sucrose into the phloem. In many dicot plants, genetic and biochemical evidence has established that SUT1-type proteins function in phloem loading. However, the role of SUT1 in phloem loading in monocot plants is not clear since the rice (Oryza sativa) and sugarcane (Saccharum hybrid) SUT1 orthologues do not appear to function in phloem loading of sucrose. A SUT1 gene was previously cloned from maize (Zea mays) and shown to have expression and biochemical activity consistent with a hypothesized role in phloem loading. To determine the biological function of SUT1 in maize, a sut1 mutant was isolated and characterized. sut1 mutant plants hyperaccumulate carbohydrates in mature leaves and display leaf chlorosis with premature senescence. In addition, sut1 mutants have greatly reduced stature, altered biomass partitioning, delayed flowering, and stunted tassel development. Cold-girdling wild-type leaves to block phloem transport phenocopied the sut1 mutants, supporting a role for maize SUT1 in sucrose export. Furthermore, application of (14)C-sucrose to abraded sut1 mutant and wild-type leaves showed that sucrose export was greatly diminished in sut1 mutants compared with wild type. Collectively, these data demonstrate that SUT1 is crucial for efficient phloem loading of sucrose in maize leaves.
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Affiliation(s)
- Thomas L. Slewinski
- Department of Biology, Pennsylvania State University, 208 Mueller Lab, University Park, PA 16802, USA
| | - Robert Meeley
- Pioneer Hi-Bred International, Incorporated, Johnston, IA 50131 USA
| | - David M. Braun
- Department of Biology, Pennsylvania State University, 208 Mueller Lab, University Park, PA 16802, USA
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Braun DM, Slewinski TL. Genetic control of carbon partitioning in grasses: roles of sucrose transporters and tie-dyed loci in phloem loading. PLANT PHYSIOLOGY 2009; 149:71-81. [PMID: 19126697 PMCID: PMC2613709 DOI: 10.1104/pp.108.129049] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2008] [Accepted: 10/19/2008] [Indexed: 05/18/2023]
Affiliation(s)
- David M Braun
- Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
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Ma Y, Slewinski TL, Baker RF, Braun DM. Tie-dyed1 encodes a novel, phloem-expressed transmembrane protein that functions in carbohydrate partitioning. PLANT PHYSIOLOGY 2009; 149:181-94. [PMID: 18923021 PMCID: PMC2613742 DOI: 10.1104/pp.108.130971] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2008] [Accepted: 10/10/2008] [Indexed: 05/18/2023]
Abstract
Carbon is partitioned between export from the leaf and retention within the leaf, and this process is essential for all aspects of plant growth and development. In most plants, sucrose is loaded into the phloem of carbon-exporting leaves (sources), transported through the veins, and unloaded into carbon-importing tissues (sinks). We have taken a genetic approach to identify genes regulating carbon partitioning in maize (Zea mays). We identified a collection of mutants, called the tie-dyed (tdy) loci, that hyperaccumulate carbohydrates in regions of their leaves. To understand the molecular function of Tdy1, we cloned the gene. Tdy1 encodes a novel transmembrane protein present only in grasses, although two protein domains are conserved across angiosperms. We found that Tdy1 is expressed exclusively in phloem cells of both source and sink tissues, suggesting that Tdy1 may play a role in phloem loading and unloading processes. In addition, Tdy1 RNA accumulates in protophloem cells upon differentiation, suggesting that Tdy1 may function as soon as phloem cells become competent to transport assimilates. Monitoring the movement of a fluorescent, soluble dye showed that tdy1 leaves have retarded phloem loading. However, once the dye entered into the phloem, solute transport appeared equal in wild-type and tdy1 mutant plants, suggesting that tdy1 plants are not defective in phloem unloading. Therefore, even though Tdy1 RNA accumulates in source and sink tissues, we propose that TDY1 functions in carbon partitioning by promoting phloem loading. Possible roles for TDY1 are discussed.
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Affiliation(s)
- Yi Ma
- Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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Slewinski TL, Ma Y, Baker RF, Huang M, Meeley R, Braun DM. Determining the role of Tie-dyed1 in starch metabolism: epistasis analysis with a maize ADP-glucose pyrophosphorylase mutant lacking leaf starch. J Hered 2008; 99:661-6. [PMID: 18723774 DOI: 10.1093/jhered/esn062] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In regions of their leaves, tdy1-R mutants hyperaccumulate starch. We propose 2 alternative hypotheses to account for the data, that Tdy1 functions in starch catabolism or that Tdy1 promotes sucrose export from leaves. To determine whether Tdy1 might function in starch breakdown, we exposed plants to extended darkness. We found that the tdy1-R mutant leaves retain large amounts of starch on prolonged dark treatment, consistent with a defect in starch catabolism. To further test this hypothesis, we identified a mutant allele of the leaf expressed small subunit of ADP-glucose pyrophosphorylase (agps-m1), an enzyme required for starch synthesis. We determined that the agps-m1 mutant allele is a molecular null and that plants homozygous for the mutation lack transitory leaf starch. Epistasis analysis of tdy1-R; agps-m1 double mutants demonstrates that Tdy1 function is independent of starch metabolism. These data suggest that Tdy1 may function in sucrose export from leaves.
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Affiliation(s)
- Thomas L Slewinski
- Department of Biology, 208 Mueller Lab, Pennsylvania State University, University Park, PA 16802, USA
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Baker RF, Braun DM. Tie-dyed2 functions with tie-dyed1 to promote carbohydrate export from maize leaves. PLANT PHYSIOLOGY 2008; 146:1085-97. [PMID: 18218972 PMCID: PMC2259043 DOI: 10.1104/pp.107.111476] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2007] [Accepted: 01/14/2008] [Indexed: 05/22/2023]
Abstract
Regulation of carbon partitioning is essential for plant growth and development. To gain insight into genes controlling carbon allocation in leaves, we identified mutants that hyperaccumulate carbohydrates. tie-dyed2 (tdy2) is a recessive mutant of maize (Zea mays) with variegated, nonclonal, chlorotic leaf sectors containing excess starch and soluble sugars. Consistent with a defect in carbon export, we found that a by-product of functional chloroplasts, likely a sugar, induces tdy2 phenotypic expression. Based on the phenotypic similarities between tdy2 and two other maize mutants with leaf carbon accumulation defects, tdy1 and sucrose export defective1 (sxd1), we investigated whether Tdy2 functioned in the same pathway as Tdy1 or Sxd1. Cytological and genetic studies demonstrate that Tdy2 and Sxd1 function independently. However, in tdy1/+; tdy2/+ F(1) plants, we observed a moderate chlorotic sectored phenotype, suggesting that the two genes are dosage sensitive and have a related function. This type of genetic interaction is referred to as second site noncomplementation and has often, though not exclusively, been found in cases where the two encoded proteins physically interact. Moreover, tdy1; tdy2 double mutants display a synergistic interaction supporting this hypothesis. Additionally, we determined that cell walls of chlorotic leaf tissues in tdy mutants contain increased cellulose; thus, tdy mutants potentially represent enhanced feedstocks for biofuels production. From our phenotypic and genetic characterizations, we propose a model whereby TDY1 and TDY2 function together in a single genetic pathway, possibly in homo- and heteromeric complexes, to promote carbon export from leaves.
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Affiliation(s)
- R Frank Baker
- Department of Biology, Pennsylvania State University, University Park, PA 16802, USA
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