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Nishii K, Möller M, Foster RG, Forrest LL, Kelso N, Barber S, Howard C, Hart ML. A high quality, high molecular weight DNA extraction method for PacBio HiFi genome sequencing of recalcitrant plants. PLANT METHODS 2023; 19:41. [PMID: 37120601 PMCID: PMC10148486 DOI: 10.1186/s13007-023-01009-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Accepted: 03/20/2023] [Indexed: 05/03/2023]
Abstract
BACKGROUND PacBio HiFi sequencing provides highly accurate long-read sequencing datasets which are of great advantage for whole genome sequencing projects. One limitation of the method is the requirement for high quality, high molecular weight input DNA. This can be particularly challenging for plants that frequently contain common and species-specific secondary metabolites, which often interfere with downstream processes. Cape Primroses (genus Streptocarpus), are some of these recalcitrant plants and are selected here as material to develop a high quality, high molecular weight DNA extraction protocol for long read genome sequencing. RESULTS We developed a DNA extraction method for PacBio HiFi sequencing for Streptocarpus grandis and Streptocarpus kentaniensis. A CTAB lysis buffer was employed to avoid guanidine, and the traditional chloroform and phenol purification steps were replaced with pre-lysis sample washes. Best cells/nucleus lysis was achieved with 4 h at 58 °C. The obtained high quality and high molecular weight DNAs were tested in PacBio SMRTBell™ library preparations, which resulted in circular consensus sequencing (CCS) reads from 17 to 27 Gb per cell, and a read length N50 from 14 to 17 kbp. To evaluate the quality of the reads for whole genome sequencing, they were assembled with HiFiasm into draft genomes, with N50 = 49 Mb and 23 Mb, and L50 = 10 and 11. The longest contigs were 95 Mb and 57 Mb respectively, showing good contiguity as these are longer than the theoretical chromosome length (genome size/chromosome number) of 78 Mb and 55 Mb, for S. grandis and S. kentaniensis respectively. CONCLUSIONS DNA extraction is a critical step towards obtaining a complete genome assembly. Our DNA extraction method here provided the required high quality, high molecular weight DNA for successful standard-input PacBio HiFi library preparation. The contigs from those reads showed a high contiguity, providing a good starting draft assembly towards obtaining a complete genome. The results obtained here were highly promising, and demonstrated that the DNA extraction method developed here is compatible with PacBio HiFi sequencing and suitable for de novo whole genome sequencing projects of plants.
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Affiliation(s)
- Kanae Nishii
- Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh, EH3 5LR UK
- Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 259-1293 Japan
| | - Michael Möller
- Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh, EH3 5LR UK
| | - Robert G. Foster
- Edinburgh Genomics, The University of Edinburgh, Charlotte Auerbach Rd., Edinburgh, EH9 3FL UK
| | - Laura L. Forrest
- Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh, EH3 5LR UK
| | - Nathan Kelso
- Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh, EH3 5LR UK
| | - Sadie Barber
- Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh, EH3 5LR UK
| | - Caroline Howard
- Wellcome Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Saffron Walden, CB10 1RQ UK
| | - Michelle L. Hart
- Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh, EH3 5LR UK
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Kinoshita A, Tsukaya H. Auxin and cytokinin control fate determination of cotyledons in the one-leaf plant Monophyllaea glabra. FRONTIERS IN PLANT SCIENCE 2022; 13:980138. [PMID: 36119619 PMCID: PMC9481249 DOI: 10.3389/fpls.2022.980138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Accepted: 08/17/2022] [Indexed: 06/15/2023]
Abstract
One-leaf plants in the Gesneriaceae family initially have two cotyledons of identical size; one cotyledon stops growing shortly after germination, whereas the other continues indeterminate growth. Factors involved in the unequal growth have been investigated, and a competitive relationship between the two cotyledons was previously proposed. However, questions regarding the fate determination of the two cotyledons remain: Why does only one cotyledon grow indeterminately while the other stops; is the fate of the cotyledons reversible; and what role does light quality play in the fate determination of the cotyledons? In this study, physiological experiments using the one-leaf plant species Monophyllaea glabra suggest that a biased auxin concentration between the two cotyledons and subsequent cytokinin levels may determine the fate of the cotyledons. In addition, observation of relatively mature individuals without hormone treatment and younger individuals with cytokinin treatment under laboratory growth conditions revealed that the fate determination of the microcotyledon is reversible. Although light quality has been suggested to be important for the determination of cotyledon fate in Streptocarpus rexii, an anisocotylous species, we conclude that light quality is not important in M. glabra.
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Nishii K, Hart M, Kelso N, Barber S, Chen Y, Thomson M, Trivedi U, Twyford AD, Möller M. The first genome for the Cape Primrose Streptocarpus rexii (Gesneriaceae), a model plant for studying meristem-driven shoot diversity. PLANT DIRECT 2022; 6:e388. [PMID: 35388373 PMCID: PMC8977575 DOI: 10.1002/pld3.388] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 01/26/2022] [Accepted: 01/30/2022] [Indexed: 05/16/2023]
Abstract
Cape Primroses (Streptocarpus, Gesneriaceae) are an ideal study system for investigating the genetics underlying species diversity in angiosperms. Streptocarpus rexii has served as a model species for plant developmental research for over five decades due to its unusual extended meristem activity present in the leaves. In this study, we sequenced and assembled the complete nuclear, chloroplast, and mitochondrial genomes of S. rexii using Oxford Nanopore Technologies long read sequencing. Two flow cells of PromethION sequencing resulted in 32 billion reads and were sufficient to generate a draft assembly including the chloroplast, mitochondrial and nuclear genomes, spanning 776 Mbp. The final nuclear genome assembly contained 5,855 contigs, spanning 766 Mbp of the 929-Mbp haploid genome with an N50 of 3.7 Mbp and an L50 of 57 contigs. Over 70% of the draft genome was identified as repeats. A genome repeat library of Gesneriaceae was generated and used for genome annotation, with a total of 45,045 genes annotated in the S. rexii genome. Ks plots of the paranomes suggested a recent whole genome duplication event, shared between S. rexii and Primulina huaijiensis. A new chloroplast and mitochondrial genome assembly method, based on contig coverage and identification, was developed, and successfully used to assemble both organellar genomes of S. rexii. This method was developed into a pipeline and proved widely applicable. The nuclear genome of S. rexii and other datasets generated and reported here will be invaluable resources for further research to aid in the identification of genes involved in morphological variation underpinning plant diversification.
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Affiliation(s)
- Kanae Nishii
- Royal Botanic Garden EdinburghEdinburghUK
- Kanagawa UniversityHiratsukaJapan
| | | | | | | | - Yun‐Yu Chen
- Royal Botanic Garden EdinburghEdinburghUK
- Institute of Molecular Plant SciencesThe University of EdinburghEdinburghUK
| | - Marian Thomson
- Edinburgh Genomics, Ashworth LaboratoriesThe University of EdinburghEdinburghUK
| | - Urmi Trivedi
- Edinburgh Genomics, Ashworth LaboratoriesThe University of EdinburghEdinburghUK
| | - Alex D. Twyford
- Royal Botanic Garden EdinburghEdinburghUK
- Institute of Evolutionary Biology, Ashworth LaboratoriesThe University of EdinburghEdinburghUK
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Kinoshita A, Koga H, Tsukaya H. Expression Profiles of ANGUSTIFOLIA3 and SHOOT MERISTEMLESS, Key Genes for Meristematic Activity in a One-Leaf Plant Monophyllaea glabra, Revealed by Whole-Mount In Situ Hybridization. FRONTIERS IN PLANT SCIENCE 2020; 11:1160. [PMID: 32903463 PMCID: PMC7435058 DOI: 10.3389/fpls.2020.01160] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2020] [Accepted: 07/16/2020] [Indexed: 05/18/2023]
Abstract
Members of the genus Monophyllaea are unique in that they produce no new organ during the vegetative phase in the shoot; instead, one of the cotyledons grows indeterminately. The mechanism of this unique trait is unclear, in part because of the lack of suitable assessment techniques. We therefore established a whole-mount in situ hybridization technique, a powerful means of examining spatial patterns in gene expression, for Monophyllaea glabra. By using this, we examined the expression pattern of a SHOOT MERISTEMLESS (STM) ortholog, which is indispensable for the formation and maintenance of the shoot apical meristem (SAM) in typical angiosperms. Expression was confined to the groove meristem (GM), which corresponds to the SAM. We also assessed the expression pattern of ANGUSTIFOLIA3 (AN3), a key promoter for cell division in the leaf meristem. It was expressed not only in the basal meristem (BM) tissue with active cell division in the basal part of the growing cotyledon but also in the GM. The findings suggest that the unusual gene expression pattern of the GM underpins the fuzzy morphogenesis of Monophyllaea.
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Affiliation(s)
- Ayaka Kinoshita
- Graduate School of Science, The University of Tokyo, Tokyo, Japan
| | - Hiroyuki Koga
- Graduate School of Science, The University of Tokyo, Tokyo, Japan
| | - Hirokazu Tsukaya
- Graduate School of Science, The University of Tokyo, Tokyo, Japan
- Exploratory Research Center on Life and Living Systems, National Institutes of Natural Sciences, Okazaki, Japan
- *Correspondence: Hirokazu Tsukaya,
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Kinoshita A, Tsukaya H. One-leaf plants in the Gesneriaceae: Natural mutants of the typical shoot system. Dev Growth Differ 2018; 61:25-33. [PMID: 30565219 DOI: 10.1111/dgd.12582] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2018] [Revised: 10/31/2018] [Accepted: 10/31/2018] [Indexed: 01/28/2023]
Abstract
The aerial part of seed plants is called the shoot, which is composed of stems, leaves, and axial buds. These are produced by indeterminate activity in the shoot apical meristem (SAM), whereas the morphogenesis of leaves depends on determinate activity of leaf meristems. However, one-leaf plants in the Gesneriaceae family (eudicots) do not have a typical SAM and do not produce new organs when in the vegetative phase. Instead, they have one cotyledon whose growth is indeterminate. This peculiar development is supported by the groove meristem, which corresponds to the canonical SAM, and the basal meristem, which corresponds to the typical leaf meristem. However, the former does not produce any organ and the latter is active indeterminately. Gene expression and physiological analyses have been conducted in an effort to determine the molecular nature of this peculiar organogenesis. This review summarizes the current understanding of the development of one-leaf plants to provide future perspectives in this field of research.
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Affiliation(s)
- Ayaka Kinoshita
- Graduate School of Science, The University of Tokyo, Tokyo, Japan
| | - Hirokazu Tsukaya
- Graduate School of Science, The University of Tokyo, Tokyo, Japan.,Exploratory Research Center on Life and Living Systems, National Institutes of Natural Sciences, Okazaki, Japan
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From shoot to leaf: step-wise shifts in meristem and KNOX1 activity correlate with the evolution of a unifoliate body plan in Gesneriaceae. Dev Genes Evol 2016; 227:41-60. [PMID: 27928690 DOI: 10.1007/s00427-016-0568-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2016] [Accepted: 11/24/2016] [Indexed: 10/20/2022]
Abstract
Typical dicots possess equal-sized cotyledons and leaf-bearing shoots topped with a shoot apical meristem (SAM), the source of lateral organs, and where KNOX1 homeobox genes act as key regulators. New World Gesneriaceae show typical cotyledons, whereas Old World Gesneriaceae show anisocotyly, the unequal post-germination growth of cotyledons, and include unifoliate (one-leaf) plants. One-leaf plants show an extremely reduced body plan: the adult above-ground photosynthetic tissue consisting of a single cotyledon, a macrocotyledon enlarged by the basal meristem (BM), but lacking a SAM. To investigate the origin and evolution of the BM and one-leaf plants, the meristem activity and KNOX1 SHOOTMERISTEMLESS (STM) expression in cotyledons and leaves were systematically studied by RT-PCR and in situ hybridization across the family Gesneriaceae, Jovellana in Calceolariaceae (sister family to Gesneriaceae), and Antirrhinum in Plantaginaceae, all families of order Lamiales (asterids), in comparison to Arabidopsis (Brassicales, rosids). In all examined Lamiales samples, unlike Arabidopsis, BM activity accompanied by STM expression was found in both cotyledons in early stages. Foliage leaves of Gesneriaceae and Jovellana also showed the correlation of BM and STM expression. An extension of BM activity was found following a phylogenetic trajectory towards one-leaf plants where it is active throughout the lifetime of the macrocotyledon. Our results suggest that KNOX1 involvement in early cotyledon expansion originated early on in the diversification of Lamiales and is proposed as the prerequisite for the evolution of vegetative diversity in Gesneriaceae. Step-wise morphological shifts, driven by transfers of meristematic activity, as evidenced by shifts in KNOX1 expression, may be one mechanism by which morphological diversity evolves in plants.
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Fambrini M, Pugliesi C. Usual and unusual development of the dicot leaf: involvement of transcription factors and hormones. PLANT CELL REPORTS 2013; 32:899-922. [PMID: 23549933 DOI: 10.1007/s00299-013-1426-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Revised: 03/15/2013] [Accepted: 03/15/2013] [Indexed: 06/02/2023]
Abstract
Morphological diversity exhibited by higher plants is essentially related to the tremendous variation of leaf shape. With few exceptions, leaf primordia are initiated postembryonically at the flanks of a group of undifferentiated and proliferative cells within the shoot apical meristem (SAM) in characteristic position for the species and in a regular phyllotactic sequence. Auxin is critical for this process, because genes involved in auxin biosynthesis, transport, and signaling are required for leaf initiation. Down-regulation of transcription factors (TFs) and cytokinins are also involved in the light-dependent leaf initiation pathway. Furthermore, mechanical stresses in SAM determine the direction of cell division and profoundly influence leaf initiation suggesting a link between physical forces, gene regulatory networks and biochemical gradients. After the leaf is initiated, its further growth depends on cell division and cell expansion. Temporal and spatial regulation of these processes determines the size and the shape of the leaf, as well as the internal structure. A complex array of intrinsic signals, including phytohormones and TFs control the appropriate cell proliferation and differentiation to elaborate the final shape and complexity of the leaf. Here, we highlight the main determinants involved in leaf initiation, epidermal patterning, and elaboration of lamina shape to generate small marginal serrations, more deep lobes or a dissected compound leaf. We also outline recent advances in our knowledge of regulatory networks involved with the unusual pattern of leaf development in epiphyllous plants as well as leaf morphology aberrations, such as galls after pathogenic attacks of pests.
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Affiliation(s)
- Marco Fambrini
- Dipartimento di Scienze Agrarie, Ambientali e Agro-alimentari, Università di Pisa, Via Del Borghetto 80, 56124 Pisa, Italy
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Nishii K, Möller M, Kidner C, Spada A, Mantegazza R, Wang CN, Nagata T. A complex case of simple leaves: indeterminate leaves co-express ARP and KNOX1 genes. Dev Genes Evol 2010; 220:25-40. [PMID: 20502914 DOI: 10.1007/s00427-010-0326-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2009] [Accepted: 04/15/2010] [Indexed: 10/19/2022]
Abstract
The mutually exclusive relationship between ARP and KNOX1 genes in the shoot apical meristem and leaf primordia in simple leaved plants such as Arabidopsis has been well characterized. Overlapping expression domains of these genes in leaf primordia have been described for many compound leaved plants such as Solanum lycopersicum and Cardamine hirsuta and are regarded as a characteristic of compound leaved plants. Here, we present several datasets illustrating the co-expression of ARP and KNOX1 genes in the shoot apical meristem, leaf primordia, and developing leaves in plants with simple leaves and simple primordia. Streptocarpus plants produce unequal cotyledons due to the continued activity of a basal meristem and produce foliar leaves termed "phyllomorphs" from the groove meristem in the acaulescent species Streptocarpus rexii and leaves from a shoot apical meristem in the caulescent Streptocarpus glandulosissimus. We demonstrate that the simple leaves in both species possess a greatly extended basal meristematic activity that persists over most of the leaf's growth. The area of basal meristem activity coincides with the co-expression domain of ARP and KNOX1 genes. We suggest that the co-expression of ARP and KNOX1 genes is not exclusive to compound leaved plants but is associated with foci of meristematic activity in leaves.
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Affiliation(s)
- Kanae Nishii
- Institute of Ecology and Evolutionary Biology, Department of Life Science, National Taiwan University, No. 1 Sec. 4 Roosevelt Road, Taipei, Taiwan, Republic of China.
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Płachno BJ, Swiatek P. Unusual embryo structure in viviparous Utricularia nelumbifolia, with remarks on embryo evolution in genus Utricularia. PROTOPLASMA 2010; 239:69-80. [PMID: 19921393 DOI: 10.1007/s00709-009-0084-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Accepted: 10/22/2009] [Indexed: 05/21/2023]
Abstract
In most species of the Genlisea-Utricularia sister lineage, the organs arising directly after germination comprise a single leaf-like structure, followed by a bladder-trap/stolon, with the lack of an embryonic primary root considered a synapomorphic character. Previous anatomical work suggests that the most common recent ancestor of Utricularia possessed an embryo comprising storage tissue and a meristematic apical region minus lateral organs. Studies of embryogenesis across the Utricularia lineage suggest that multiple primary organs have only evolved in the viviparous Utricularia nelumbifolia, Utricularia reniformis, and Utricularia humboldtii within the derived Iperua/Orchidioides clade. All three of these species are specialized for growth as "aquatic epiphytes" in the tanks of bromeliads, with recent phylogenetic evidence suggesting the possibility that multiple primary organs may have evolved twice independently within this clade. The primary organs of viviparous Utricularia also possess epidermal surface glands, and our study suggests that these may function as root hairs for uptake of solutes from the external environment--a possible adaptation for the "aquatic-epiphytic" habitat.
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Affiliation(s)
- Bartosz J Płachno
- Department of Plant Cytology and Embryology, Jagiellonian University, Krakow, Poland.
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Barth S, Geier T, Eimert K, Watillon B, Sangwan RS, Gleissberg S. KNOX overexpression in transgenic Kohleria (Gesneriaceae) prolongs the activity of proximal leaf blastozones and drastically alters segment fate. PLANTA 2009; 230:1081-91. [PMID: 19685246 DOI: 10.1007/s00425-009-0997-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Accepted: 07/21/2009] [Indexed: 05/11/2023]
Abstract
KNOX (knotted1-like homeobox) genes have a widely conserved role in the generation of dissected leaves. Ectopic KNOX activity in leaves in various angiosperm lineages causes leaf form changes that can elucidate how the configuration of leaf development evolved. We present an analysis of leaf morphology and morphogenesis in transgenic Kohleria lines overexpressing a heterologous KNOX gene. Kohleria, like many members of Gesneriaceae, has simple-serrated leaves with pinnate venation. KNOX overexpression causes prolonged segment proliferation in proximal, but not distal, parts of leaf blades. Elaborate dissected segments reiterate the zonation of the whole leaf, with organogenic activity persisting between a distal maturation zone and a proximal intercalary elongation zone. The architecture of vascular bundles is severely altered, with a reduced midvein and a more palmate venation. The initial establishment of organogenically competent primordial margins (marginal blastozones) and the onset of tissue differentiation in early stages of leaf development were similar in wild-type and KNOX overexpressing lines. However, leaves overexpressing KNOX often failed to fully mature, and persistent marginal blastozones were found at the base of blades in mature portions of the shoot. We conclude that KNOX-mediated perpetuation of marginal blastozones in Kohleria is sufficient to induce a set of processes that result in highly dissected leaflets, which are unusual in this plant family. Spatial confinement of blastozones between an early maturing tip and a late elongating petiole zone reflects the presence of distinct maturation processes that limit the ability of the leaf margins to respond to ectopic KNOX gene expression.
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Affiliation(s)
- Sina Barth
- Institut fuer Spezielle Botanik, University of Mainz, Mainz, Germany
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Mantegazza R, Tononi P, Möller M, Spada A. WUS and STM homologs are linked to the expression of lateral dominance in the acaulescent Streptocarpus rexii (Gesneriaceae). PLANTA 2009; 230:529-542. [PMID: 19526368 DOI: 10.1007/s00425-009-0965-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2009] [Accepted: 05/28/2009] [Indexed: 05/27/2023]
Abstract
Acaulescent species of Streptocarpus Lindl. show unusual patterns of growth, characterized by anisocotyly (i.e. the unequal growth of cotyledons after germination) and lack of a conventional embryonic shoot apical meristem (SAM). A SAM-like structure appears during post-embryonic development on the axis of the continuously growing cotyledon. Since we have shown previously that KNOX genes are involved in this unusual morphology of Streptocarpus rexii, here we investigated the expression pattern of WUSCHEL (WUS), which is also required for the indeterminacy of the SAM, but is expressed independently from KNOX in Arabidopsis thaliana. In A. thaliana WUSCHEL is involved in the maintenance of the stem cell fate in the organizing centre. The expression pattern of the WUS ortholog in S. rexii (SrWUS) strongly deviates from that of the model plant, suggesting a fundamentally different spatial and temporal regulation of signalling involved in meristem initiation and maintenance. In S. rexii, exogenous application of growth regulators, i.e. gibberellin (GA(3)), cytokinin (CK) and a gibberellin biosynthesis inhibitor (PAC), prevents anisocotyly and relocates meristematic cells to a position of conventional SAMs; this coincides with a re-localization of the two main pathways controlling meristem formation, the SrWUS and the KNOX pathways. Our results suggest that the establishment of a hormone imbalance in the seedlings is the basis of anisocotyly, causing a lateral dominance of the macrocotyledon over the microcotyledon. The peculiar morphogenetic program in S. rexii is linked to this delicate hormone balance and is the result of crosstalk between endogenous hormones and regulatory genes.
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Affiliation(s)
- Raffaella Mantegazza
- Dipartimento di Biologia, Università degli Studi di Milano, Via Celoria 26, 20133, Milan, Italy
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Abstract
The cotyledon represents one of the bases of classification within the plant kingdom, providing the name-giving difference between dicotyledonous and monocotyledonous plants. It is also a fundamental organ and there have been many reports of cotyledon mutants in many species. The use of these mutants where they have arisen in Arabidopsis has allowed us to unravel some of the complexities of embryonic patterning and cotyledon development with a high degree of resolution. The cloning of genes involved in cotyledon development from other species, together with physiological work, has supported the hypothesis that there exists a small number of orthologous gene hierarchies, particularly those involving auxin. The time is therefore appropriate for a summary of the regulation of cotyledon development gleaned from cotyledon mutants and regulatory pathways in the model species Arabidopsis and what can be inferred from cotyledon mutants in other species. There is an enormous variation in cotyledon form and development throughout the plant kingdom and this review focuses on debates about the phylogenetic relationship between mono- and dicotyledony, discusses gymnosperm cotyledon development and pleiocotyly in natural populations, and explores the limits of homology between cotyledons and leaves.
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Affiliation(s)
- John W Chandler
- Department of Developmental Biology, University of Cologne, Gyrhofstrasse 17, D-50923 Cologne, Germany.
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