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Burke R, McCabe A, Sonawane NR, Rathod MH, Whelan CV, McCabe PF, Kacprzyk J. Arabidopsis cell suspension culture and RNA sequencing reveal regulatory networks underlying plant-programmed cell death. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2023; 115:1465-1485. [PMID: 37531399 DOI: 10.1111/tpj.16407] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2023] [Revised: 06/27/2023] [Accepted: 07/20/2023] [Indexed: 08/04/2023]
Abstract
Programmed cell death (PCD) facilitates selective, genetically controlled elimination of redundant, damaged, or infected cells. In plants, PCD is often an essential component of normal development and can mediate responses to abiotic and biotic stress stimuli. However, studying the transcriptional regulation of PCD is hindered by difficulties in sampling small groups of dying cells that are often buried within the bulk of living plant tissue. We addressed this challenge by using RNA sequencing and Arabidopsis thaliana suspension cells, a model system that allows precise monitoring of PCD rates. The use of three PCD-inducing treatments (salicylic acid, heat, and critical dilution), in combination with three cell death modulators (3-methyladenine, lanthanum chloride, and conditioned medium), enabled isolation of candidate core- and stimuli-specific PCD genes, inference of underlying regulatory networks and identification of putative transcriptional regulators of PCD in plants. This analysis underscored a disturbance of the cell cycle and mitochondrial retrograde signaling, and repression of pro-survival stress responses, as key elements of the PCD-associated transcriptional signature. Further, phenotyping of Arabidopsis T-DNA insertion mutants in selected candidate genes validated the potential of generated resources to identify novel genes involved in plant PCD pathways and/or stress tolerance.
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Affiliation(s)
- Rory Burke
- School of Biology and Environmental Science, University College Dublin, Dublin 4, Ireland
| | - Aideen McCabe
- School of Biology and Environmental Science, University College Dublin, Dublin 4, Ireland
| | - Neetu Ramesh Sonawane
- School of Biology and Environmental Science, University College Dublin, Dublin 4, Ireland
| | - Meet Hasmukh Rathod
- School of Biology and Environmental Science, University College Dublin, Dublin 4, Ireland
| | - Conor V Whelan
- School of Biology and Environmental Science, University College Dublin, Dublin 4, Ireland
| | - Paul F McCabe
- School of Biology and Environmental Science, University College Dublin, Dublin 4, Ireland
| | - Joanna Kacprzyk
- School of Biology and Environmental Science, University College Dublin, Dublin 4, Ireland
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2
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Lu L, Yang H, Xu Y, Zhang L, Wu J, Yi H. Laser capture microdissection-based spatiotemporal transcriptomes uncover regulatory networks during seed abortion in seedless Ponkan (Citrus reticulata). THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2023; 115:642-661. [PMID: 37077034 DOI: 10.1111/tpj.16251] [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: 11/09/2022] [Revised: 04/06/2023] [Accepted: 04/12/2023] [Indexed: 05/03/2023]
Abstract
Seed abortion is an important process in the formation of seedless characteristics in citrus fruits. However, the molecular regulatory mechanism underlying citrus seed abortion is poorly understood. Laser capture microdissection-based RNA-seq combined with Pacbio-seq was used to profile seed development in the Ponkan cultivars 'Huagan No. 4' (seedless Ponkan) (Citrus reticulata) and 'E'gan No. 1' (seeded Ponkan) (C. reticulata) in two types of seed tissue across three developmental stages. Through comparative transcriptome and dynamic phytohormone analyses, plant hormone signal, cell division and nutrient metabolism-related processes were revealed to play critical roles in the seed abortion of 'Huagan No. 4'. Moreover, several genes may play indispensable roles in seed abortion of 'Huagan No. 4', such as CrWRKY74, CrWRKY48 and CrMYB3R4. Overexpression of CrWRKY74 in Arabidopsis resulted in severe seed abortion. By analyzing the downstream regulatory network, we further determined that CrWRKY74 participated in seed abortion regulation by inducing abnormal programmed cell death. Of particular importance is that a preliminary model was proposed to depict the regulatory networks underlying seed abortion in citrus. The results of this study provide novel insights into the molecular mechanism across citrus seed development, and reveal the master role of CrWRKY74 in seed abortion of 'Huagan No. 4'.
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Affiliation(s)
- Liqing Lu
- National Key Laboratory for Germplasm Innovation and Utilization of Horticultural Crops, Huazhong Agricultural University, Wuhan, 430070, P.R. China
| | - Haijian Yang
- Fruit Tree Research Institute of Chongqing Academy of Agricultural Sciences, Chongqing, 401329, P.R. China
| | - Yanhui Xu
- National Key Laboratory for Germplasm Innovation and Utilization of Horticultural Crops, Huazhong Agricultural University, Wuhan, 430070, P.R. China
| | - Li Zhang
- National Key Laboratory for Germplasm Innovation and Utilization of Horticultural Crops, Huazhong Agricultural University, Wuhan, 430070, P.R. China
| | - Juxun Wu
- National Key Laboratory for Germplasm Innovation and Utilization of Horticultural Crops, Huazhong Agricultural University, Wuhan, 430070, P.R. China
| | - Hualin Yi
- National Key Laboratory for Germplasm Innovation and Utilization of Horticultural Crops, Huazhong Agricultural University, Wuhan, 430070, P.R. China
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Rowarth NM, Curtis BA, Einfeldt AL, Archibald JM, Lacroix CR, Gunawardena AHLAN. RNA-Seq analysis reveals potential regulators of programmed cell death and leaf remodelling in lace plant (Aponogeton madagascariensis). BMC PLANT BIOLOGY 2021; 21:375. [PMID: 34388962 PMCID: PMC8361799 DOI: 10.1186/s12870-021-03066-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 05/25/2021] [Indexed: 06/13/2023]
Abstract
BACKGROUND The lace plant (Aponogeton madagascariensis) is an aquatic monocot that develops leaves with uniquely formed perforations through the use of a developmentally regulated process called programmed cell death (PCD). The process of perforation formation in lace plant leaves is subdivided into several developmental stages: pre-perforation, window, perforation formation, perforation expansion and mature. The first three emerging "imperforate leaves" do not form perforations, while all subsequent leaves form perforations via developmentally regulated PCD. PCD is active in cells called "PCD cells" that do not retain the antioxidant anthocyanin in spaces called areoles framed by the leaf veins of window stage leaves. Cells near the veins called "NPCD cells" retain a red pigmentation from anthocyanin and do not undergo PCD. While the cellular changes that occur during PCD are well studied, the gene expression patterns underlying these changes and driving PCD during leaf morphogenesis are mostly unknown. We sought to characterize differentially expressed genes (DEGs) that mediate lace plant leaf remodelling and PCD. This was achieved performing gene expression analysis using transcriptomics and comparing DEGs among different stages of leaf development, and between NPCD and PCD cells isolated by laser capture microdissection. RESULTS Transcriptomes were sequenced from imperforate, pre-perforation, window, and mature leaf stages, as well as PCD and NPCD cells isolated from window stage leaves. Differential expression analysis of the data revealed distinct gene expression profiles: pre-perforation and window stage leaves were characterized by higher expression of genes involved in anthocyanin biosynthesis, plant proteases, expansins, and autophagy-related genes. Mature and imperforate leaves upregulated genes associated with chlorophyll development, photosynthesis, and negative regulators of PCD. PCD cells were found to have a higher expression of genes involved with ethylene biosynthesis, brassinosteroid biosynthesis, and hydrolase activity whereas NPCD cells possessed higher expression of auxin transport, auxin signalling, aspartyl proteases, cysteine protease, Bag5, and anthocyanin biosynthesis enzymes. CONCLUSIONS RNA sequencing was used to generate a de novo transcriptome for A. madagascariensis leaves and revealed numerous DEGs potentially involved in PCD and leaf remodelling. The data generated from this investigation will be useful for future experiments on lace plant leaf development and PCD in planta.
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Affiliation(s)
- Nathan M Rowarth
- Department of Biology, Dalhousie University, Halifax, NS, Canada
| | - Bruce A Curtis
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, NS, Canada
| | | | - John M Archibald
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, NS, Canada
| | - Christian R Lacroix
- Department of Biology, University of Prince Edward Island, Charlottetown, PEI, Canada
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Castander-Olarieta A, Moncaleán P, Pereira C, Pěnčík A, Petřík I, Pavlović I, Novák O, Strnad M, Goicoa T, Ugarte MD, Montalbán IA. Cytokinins are involved in drought tolerance of Pinus radiata plants originating from embryonal masses induced at high temperatures. TREE PHYSIOLOGY 2021; 41:912-926. [PMID: 32348507 DOI: 10.1093/treephys/tpaa055] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Revised: 04/07/2020] [Accepted: 04/21/2020] [Indexed: 05/22/2023]
Abstract
Vegetative propagation through somatic embryogenesis is an effective method to produce elite varieties and can be applied as a tool to study the response of plants to different stresses. Several studies show that environmental changes during embryogenesis could determine future plant development. Moreover, we previously reported that physical and chemical conditions during somatic embryogenesis can determine the protein, hormone and metabolite profiles, as well as the micromorphological and ultrastructural organization of embryonal masses and somatic embryos. In this sense, phytohormones are key players throughout the somatic embryogenesis process as well as during numerous stress-adaptation responses. In this work, we first applied different high-temperature regimes (30 °C, 4 weeks; 40 °C, 4 days; 50 °C, 5 min) during induction of Pinus radiata D. Don somatic embryogenesis, together with control temperature (23 °C). Then, the somatic plants regenerated from initiated embryogenic cell lines and cultivated in greenhouse conditions were subjected to drought stress and control treatments to evaluate survival, growth and several physiological traits (relative water content, water potential, photosynthesis, stomatal conductance and transpiration). Based on those preliminary results, even more extreme high-temperature regimes were applied during induction (40 °C, 4 h; 50 °C, 30 min; 60 °C, 5 min) and the corresponding cytokinin profiles of initiated embryonal masses from different lines were analysed. The results showed that the temperature regime during induction had delayed negative effects on drought resilience of somatic plants as indicated by survival, photosynthetic activity and water- use efficiency. However, high temperatures for extended periods of time enhanced subsequent plant growth in well-watered conditions. High-temperature regime treatments induced significant differences in the profile of total cytokinin bases, N6-isopentenyladenine, cis-zeatin riboside and trans-zeatin riboside. We concluded that phytohormones could be potential regulators of stress-response processes during initial steps of somatic embryogenesis and that they may have delayed implications in further developmental processes, determining the performance of the generated plants.
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Affiliation(s)
| | | | - Catia Pereira
- Department of Forestry Science, NEIKER, Arcaute 01080, Spain
- Department of Life Sciences, Universidade de Coimbra, Coimbra 3000-456, Portugal
| | - Aleš Pěnčík
- Laboratory of Growth Regulators, Faculty of Science, Institute of Experimental Botany of the Czech Academy of Sciences, Palacký University, Olomouc 783 71, Czech Republic
| | - Ivan Petřík
- Laboratory of Growth Regulators, Faculty of Science, Institute of Experimental Botany of the Czech Academy of Sciences, Palacký University, Olomouc 783 71, Czech Republic
| | - Iva Pavlović
- Laboratory of Growth Regulators, Faculty of Science, Institute of Experimental Botany of the Czech Academy of Sciences, Palacký University, Olomouc 783 71, Czech Republic
| | - Ondřej Novák
- Laboratory of Growth Regulators, Faculty of Science, Institute of Experimental Botany of the Czech Academy of Sciences, Palacký University, Olomouc 783 71, Czech Republic
| | - Miroslav Strnad
- Laboratory of Growth Regulators, Faculty of Science, Institute of Experimental Botany of the Czech Academy of Sciences, Palacký University, Olomouc 783 71, Czech Republic
| | - Tomas Goicoa
- Department of Statistics, Computer Science and Mathematics, Universidad Pública de Navarra, Pamplona 31006, Spain
| | - Maria D Ugarte
- Department of Statistics, Computer Science and Mathematics, Universidad Pública de Navarra, Pamplona 31006, Spain
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Jacob D, Brian J. The short and intricate life of the suspensor. PHYSIOLOGIA PLANTARUM 2020; 169:110-121. [PMID: 31808953 DOI: 10.1111/ppl.13057] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Revised: 11/04/2019] [Accepted: 12/04/2019] [Indexed: 06/10/2023]
Abstract
The suspensor is a short-lived tissue critical for proper embryonic development in many higher plants. While the tissue was initially thought to simply suspend the embryo in the endosperm, it has been found through decades of research that it serves multiple important purposes. The suspensor has been found to be vital for proper embryo patterning and numerous studies have been undertaken into the complex transcriptional cross-talk between the suspensor and the embryo proper. Indeed, many suspensor mutants also display abnormalities in the embryo. The suspensor's role as a nutrient conduit has been shown using ultrastructural and histochemical techniques. Biochemical approaches have found that the suspensor is a centre of early embryonic hormone production in several species. The suspensor has also been frequently used as a model for programmed cell death as it shows signs of termination almost immediately upon developing. This review covers the essential functions of the suspensor throughout its short existence from multiple disciplines including structural, genetic and biochemical perspectives.
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Affiliation(s)
- Downs Jacob
- Faculty of Science, University of Sydney, Sydney, NSW, 2006, Australia
| | - Jones Brian
- Faculty of Science, University of Sydney, Sydney, NSW, 2006, Australia
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Li S, Yan H, Mei WM, Tse YC, Wang H. Boosting autophagy in sexual reproduction: a plant perspective. THE NEW PHYTOLOGIST 2020; 226:679-689. [PMID: 31917864 DOI: 10.1111/nph.16414] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 12/21/2019] [Indexed: 06/10/2023]
Abstract
The key process of sexual reproduction is the successful fusion of the sperm and egg cell. Distinct from dynamic and flagellated animal sperm cells, higher flowering plant sperm cells are immotile. Therefore, plants have evolved a novel reproductive system to achieve fertilization and generate progenies. Plant sexual reproduction consists of multiple steps, mainly including gametophyte development, pollen-pistil recognition, pollen germination, double fertilization and postfertilization. During reproduction, active production, consumption and recycling of cellular components and energy are critically required to achieve fertilization. However, the underlying machinery of cellular degradation and turnover remains largely unexplored. Autophagy, the major catabolic pathway in eukaryotic cells, participates in regulating multiple aspects of plant activities, including abiotic and biotic stress resistance, pathogen response, senescence, nutrient remobilization and plant development. Nevertheless, a key unanswered question is how autophagy regulates plant fertilization and reproduction. Here, we focus on comparing and contrasting autophagy in several key reproductive processes of plant and animal systems to feature important distinctions and highlight future research directions of autophagy in angiosperm reproduction. We further discuss the potential crosstalk between autophagy and programmed cell death, which are often considered as two disconnected events in plant sexual reproduction.
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Affiliation(s)
- Shanshan Li
- College of Life Sciences, South China Agricultural University, Guangzhou, 510642, China
| | - He Yan
- College of Life Sciences, South China Agricultural University, Guangzhou, 510642, China
| | - Wei-Ming Mei
- Outpatient Department of Sun Yat-sen Memorial Hospital, Sun Yat-sen University, Guangzhou, 510275, China
| | - Yu Chung Tse
- Guangdong Provincial Key Laboratory of Cell Microenvironment and Disease Research, Shenzhen Key Laboratory of Cell Microenvironment and Department of Biology, Southern University of Science and Technology, Shenzhen, 518005, China
| | - Hao Wang
- College of Life Sciences, South China Agricultural University, Guangzhou, 510642, China
- Integrative Microbiology Research Centre, South China Agricultural University, Guangzhou, 510642, China
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Liu H, Hao N, Jia Y, Liu X, Ni X, Wang M, Liu W. The ethylene receptor regulates Typha angustifolia leaf aerenchyma morphogenesis and cell fate. PLANTA 2019; 250:381-390. [PMID: 31062160 DOI: 10.1007/s00425-019-03177-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Accepted: 04/26/2019] [Indexed: 05/14/2023]
Abstract
Ethylene receptor is crucial for PCD and aerenchyma formation in Typha angustifolia leaves. Not only does it receive and deliver the ethylene signal, but it probably can determine the cell fate during aerenchyma morphogenesis, which is due to the receptor expression quantity. Aquatic plant oxygen delivery relies on aerenchyma, which is formed by a programmed cell death (PCD) procedure. However, cells in the outer edge of the aerenchyma (palisade cells and septum cells) remain intact, and the mechanism is unclear. Here, we offer a hypothesis: cells that have a higher content of ethylene receptors do not undergo PCD. In this study, we investigated the leaf aerenchyma of the aquatic plant Typha angustifolia. Ethephon and pyrazinamide (PZA, an inhibitor of ACC oxidase) were used to confirm that ethylene is an essential hormone for PCD of leaf aerenchyma cells in T. angustifolia. That the ethylene receptor was an indispensable factor in this PCD was confirmed by 1-MCP (an inhibitor of the ethylene receptor) treatment. Although PCD can be avoided by blocking the ethylene receptor, excessive ethylene receptors also protect cells from PCD. TaETR1, TaETR2 and TaEIN4 in the T. angustifolia leaf were detected by immunofluorescence (IF) using polyclonal antibodies. The result showed that the content of ethylene receptors in PCD-unsusceptible cells was 4-14 times higher than that one in PCD-susceptible cells, suggesting that PCD-susceptible cells undergo the PCD programme, while PCD-unsusceptible cells do not due to the content difference in the ethylene receptor in different cells. A higher level of ethylene receptor content makes the cells insensitive to ethylene, thereby avoiding cell death and degradation.
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Affiliation(s)
- Huidong Liu
- Key Laboratory of Resource Biology and Biotechnology in Western China, Northwest University, Ministry of Education, Xi'an, 710069, China
| | - Nan Hao
- Key Laboratory of Resource Biology and Biotechnology in Western China, Northwest University, Ministry of Education, Xi'an, 710069, China
| | - Yuhuan Jia
- Key Laboratory of Resource Biology and Biotechnology in Western China, Northwest University, Ministry of Education, Xi'an, 710069, China
| | - Xingqian Liu
- Key Laboratory of Resource Biology and Biotechnology in Western China, Northwest University, Ministry of Education, Xi'an, 710069, China
| | - Xilu Ni
- State Key Laboratory of Seedling Bioengineering, Ningxia Forestry Institute, Yinchuan, 750004, China
| | - Meng Wang
- Key Laboratory of Resource Biology and Biotechnology in Western China, Northwest University, Ministry of Education, Xi'an, 710069, China
| | - Wenzhe Liu
- Key Laboratory of Resource Biology and Biotechnology in Western China, Northwest University, Ministry of Education, Xi'an, 710069, China.
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Klemenčič M, Funk C. Evolution and structural diversity of metacaspases. JOURNAL OF EXPERIMENTAL BOTANY 2019; 70:2039-2047. [PMID: 30921456 DOI: 10.1093/jxb/erz082] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 01/09/2019] [Indexed: 06/09/2023]
Abstract
Caspases are metazoan proteases, best known for their involvement in programmed cell death in animals. In higher plants genetically controlled mechanisms leading to the selective death of individual cells also involve the regulated interplay of various types of proteases. Some of these enzymes are structurally homologous to caspases and have therefore been termed metacaspases. In addition to the two well-studied metacaspase variants found in higher plants, type I and type II, biochemical data have recently become available for metacaspases of type III and metacaspase-like proteases, which are present only in certain algae. Although increasing in vitro and in vivo data suggest the existence of further sub-types, a lack of structural information hampers the interpretation of their distinct functional properties. However, the identification of key amino acid residues involved in the proteolytic mechanism of metacaspases, as well as the increased availability of plant genomic and transcriptomic data, is increasingly enabling in-depth analysis of all metacaspase types found in plastid-containing organisms. Here, we review the structural distribution and diversification of metacaspases and in doing so try to provide comprehensive guidelines for further analyses of this versatile family of proteases in organisms ranging from simple unicellular species to flowering plants.
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Affiliation(s)
- Marina Klemenčič
- Department of Chemistry, Umeå University, Umeå, Sweden
- Department of Chemistry and Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot, Ljubljana, Slovenia
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Buono RA, Hudecek R, Nowack MK. Plant proteases during developmental programmed cell death. JOURNAL OF EXPERIMENTAL BOTANY 2019; 70:2097-2112. [PMID: 30793182 PMCID: PMC7612330 DOI: 10.1093/jxb/erz072] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Accepted: 02/12/2019] [Indexed: 05/08/2023]
Abstract
Proteases are among the key regulators of most forms of programmed cell death (PCD) in animals. Many PCD processes have also been associated with protease expression or activation in plants, However, functional evidence for the roles and actual modes of action of plant proteases in PCD remains surprisingly limited. In this review, we provide an update on protease involvement in the context of developmentally regulated plant PCD. To illustrate the diversity of protease functions, we focus on several prominent developmental PCD processes, including xylem and tapetum maturation, suspensor elimination, endosperm degradation, and seed coat formation, as well as plant senescence processes. Despite the substantial advances in the field, protease functions are often only correlatively linked to developmental PCD, and the specific molecular roles of proteases in many developmental PCD processes remain to be elucidated.
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Affiliation(s)
- Rafael Andrade Buono
- Department of Plant Biotechnology and Genetics, Ghent University, 9052 Ghent, Belgium
- VIB Center for Plant Systems Biology, 9052 Ghent, Belgium
| | - Roman Hudecek
- Department of Plant Biotechnology and Genetics, Ghent University, 9052 Ghent, Belgium
- VIB Center for Plant Systems Biology, 9052 Ghent, Belgium
| | - Moritz K. Nowack
- Department of Plant Biotechnology and Genetics, Ghent University, 9052 Ghent, Belgium
- VIB Center for Plant Systems Biology, 9052 Ghent, Belgium
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Díaz-Sala C. Molecular Dissection of the Regenerative Capacity of Forest Tree Species: Special Focus on Conifers. FRONTIERS IN PLANT SCIENCE 2018; 9:1943. [PMID: 30687348 PMCID: PMC6333695 DOI: 10.3389/fpls.2018.01943] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Accepted: 12/13/2018] [Indexed: 05/21/2023]
Abstract
Somatic embryogenesis (SE) and organogenesis have become leading biotechnologies for forest tree improvement and the implementation of multi-varietal forestry. Despite major advances in clonal propagation using these technologies, many forest tree species, such as conifers, show a low regeneration capacity. Developmental factors such as genotype, the type and age of the explant or tissue, and the age and maturity of the mother tree are limiting factors for the success of propagation programs. This review summarizes recent research on the molecular pathways involved in the regulation of key steps in SE and organogenesis of forest tree species, mainly conifers. The interaction between auxin and stress conditions, the induction of cell identity regulators and the role of cell wall remodeling are reviewed. This information is essential to develop tools and strategies to improve clonal propagation programs for forest tree species.
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