Initiation of shoot apical meristem in rice: characterization of four SHOOTLESS genes

The regulatory mechanism of shoot apical meristem (SAM) initiation is an important subject in developmental plant biology. We characterized nine recessive mutations derived from four independent loci (SHL1-SHL4) causing the deletion of the SAM. Radicles were produced in these mutant embryos. Concomitant with the loss of SAM, two embryo-specific organs, coleoptile and epiblast, were lost, but the scutellum was formed normally. Therefore, differentiation of radicle and scutellum is regulated independently of SAM, but that of coleoptile and epiblast may depend on SAM. Regeneration experiments using adventitious shoots from the scutellum-derived calli showed that no adventitious shoots were regenerated in any shl mutant. However, small adventitious leaves were observed in both mutant and wild-type calli, but they soon became necrotic and showed no extensive growth. Thus, leaf primordia can initiate in the absence of SAM, but their extensive growth requires the SAM. An in situ hybridization experiment using a rice homeobox gene, OSH1, as a probe revealed that shl1 and shl2 modified the expression domain of OSH1, but normal expression of OSH1 was observed in shl3 and shl4 embryos. Accordingly, SHL1 and SHL2 function upstream of OSH1, and SHL3 and SHL4 downstream or independently of OSH1. These shl mutants are useful for elucidating the genetic program driving SAM initiation and for unraveling the interrelationships among various organs in grass embryos.

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Extended expression of MaKN1 contributes to the leaf morphology in aquatic forms of Myriophyllum aquaticum

Botany ◽

10.1139/cjb-2015-0077 ◽

2015 ◽

Vol 93 (9) ◽

pp. 611-621

Author(s):

M.D. Shafiullah ◽

Christian R. Lacroix

Keyword(s):

Apical Meristem ◽

Leaf Morphology ◽

Expression Patterns ◽

Homeobox Gene ◽

Leaf Primordia ◽

Leaf Primordium ◽

Myriophyllum Aquaticum ◽

Knox Gene ◽

Leaf Morphogenesis

Myriophyllum aquaticum (Vell.) Verdc. is heterophyllous in nature with highly dissected simple leaves consisting of several lobes. KNOX (KNOTTED1-LIKE HOMEOBOX) genes are believed to have played an important role in the evolution of leaf diversity. Up-regulation of KNOX during leaf primordium initiation can lead to leaf dissection in plants with simple leaves and, if overexpressed, can produce ectopic meristems on leaves. A previous study on KNOX gene expression in the aerial form of this species showed that this gene is expressed in the shoot apical meristem (SAM), as well as in leaf primordia P0 to P8. Based on these results, it was hypothesized that the prolonged expression of the MaKN1 (Myriophyllum aquaticum Knotted1-like homeobox) gene beyond P8, might play an important role in the generation of more lobes, longer lobes, and hydathode formation in the aquatic leaves of M. aquaticum. The technique of in situ hybridization was carried out using a previously sequenced 300 bp fragment of MaKN1 to determine the expression patterns of this gene in the shoot of aquatic forms of the plant. Expression patterns of MaKN1 revealed that the SAM and leaf primordia of aquatic forms of M. aquaticum at levels P0 (youngest) to P4 were distributed throughout these structures. The level of expression of this MaKN1 gene progressively became more localized to lobes in older leaf primordia (levels P5 to P12). Previous studies of aerial forms of this plant showed MaKN1 expression until P8. Our results with aquatic forms show that the highly dissected leaf morphology in aquatic forms was the result of the prolonged expression of MaKN1 beyond P8. This resulted in the formation of elongated and slightly more numerous lobes, and hydathodes in aquatic forms. These findings support the view that KNOX genes are important developmental regulators of leaf morphogenesis and have played an important role in the evolution of leaf forms in the plant kingdom.

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Modeling the organization of the WUSCHEL expression domain in the shoot apical meristem

Bioinformatics ◽

10.1093/bioinformatics/bti1036 ◽

2005 ◽

Vol 21 (Suppl 1) ◽

pp. i232-i240 ◽

Cited By ~ 83

Author(s):

H. Jonsson ◽

M. Heisler ◽

G. V. Reddy ◽

V. Agrawal ◽

V. Gor ◽

...

Keyword(s):

Shoot Apical Meristem ◽

Apical Meristem ◽

Expression Domain

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Characterisation of three shoot apical meristem mutants of Arabidopsis thaliana

Development ◽

10.1242/dev.116.2.397 ◽

1992 ◽

Vol 116 (2) ◽

pp. 397-403 ◽

Cited By ~ 19

Author(s):

H. M. Ottoline Leyser ◽

I. J. Furner

Keyword(s):

Arabidopsis Thaliana ◽

Root Growth ◽

Shoot Apical Meristem ◽

Apical Meristem ◽

Floral Development ◽

Wild Type ◽

Recessive Mutations ◽

Phenotypic Characterisation ◽

Dicotyledonous Plants ◽

And Function

The shoot apical meristem of dicotyledonous plants is highly regulated both structurally and functionally, but little is known about the mechanisms involved in this regulation. Here we describe the genetic and phenotypic characterisation of recessive mutations at three loci of Arabidopsis thaliana in which meristem structure and function are disrupted. The loci are Clavata1 (Clv1), Fasciata1 (Fas1) and Fasciata2 (Fas2). Plants mutant at these loci are fasciated having broad, flat stems and disrupted phyllotaxy. In all cases, the fasciations are associated with shoot apical meristem enlargement and altered floral development. While all the mutants share some phenotypic features they can be divided into two classes. The pleiotropic fas1 and fas2 mutants are unable to initiate wild- type organs, show major alterations in meristem structure and have reduced root growth. In contrast, clv1 mutant plants show near wild-type organ phenotypes, more subtle changes in shoot apical meristem structure and wild-type root growth.

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Control of phyllotaxy in maize by the abphyl1 gene

Development ◽

10.1242/dev.126.2.315 ◽

1999 ◽

Vol 126 (2) ◽

pp. 315-323 ◽

Cited By ~ 2

Author(s):

D. Jackson ◽

S. Hake

Keyword(s):

Apical Meristem ◽

General Structure ◽

Homeobox Gene ◽

The Other ◽

Shoot Meristem ◽

Regular Pattern ◽

Expression Domain ◽

Geometric Patterns ◽

Maize Plants ◽

Shoot Meristems

Organogenesis in plants occurs at the shoot apical meristem, a group of indeterminate stem cells that are organized during embryogenesis. Regulated initiation of leaves or flowers from the shoot meristem gives rise to the familiar geometric patterns observed throughout the plant kingdom. The mechanism by which these patterns, termed phyllotaxies, are generated, remains unclear. Maize plants initiate leaves singly, alternating from one side to the other in a regular pattern. Here we describe a recessive maize mutant, abphyl1, that initiates leaves in opposite pairs, in a pattern termed decussate phyllotaxy. The decussate shoot meristems are larger than normal throughout development, though the general structure and organization of the meristem is not altered. abph1 mutants are first distinguished during embryogenesis, prior to true leaf initiation, by a larger shoot meristem and coincident larger expression domain of the homeobox gene knotted1. Therefore, the abph1 gene regulates morphogenesis in the embryo, and plays a role in determining the phyllotaxy of the shoot.

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The CUP-SHAPED COTYLEDON1 gene of Arabidopsis regulates shoot apical meristem formation

Development ◽

10.1242/dev.128.7.1127 ◽

2001 ◽

Vol 128 (7) ◽

pp. 1127-1135 ◽

Cited By ~ 6

Author(s):

S. Takada ◽

K. Hibara ◽

T. Ishida ◽

M. Tasaka

Keyword(s):

Shoot Apical Meristem ◽

Apical Meristem ◽

Molecular Mechanisms ◽

Higher Plants ◽

Adventitious Shoots ◽

Floral Organ ◽

Loss Of Function ◽

Nac Domain ◽

Redundant Genes ◽

Domain Protein

In higher plants, molecular mechanisms regulating shoot apical meristem (SAM) formation and organ separation are largely unknown. The CUC1 (CUP-SHAPED COTYLEDON1) and CUC2 are functionally redundant genes that are involved in these processes. We cloned the CUC1 gene by a map-based approach, and found that it encodes a NAC-domain protein highly homologous to CUC2. CUC1 mRNA was detected in the presumptive SAM during embryogenesis, and at the boundaries between floral organ primordia. Surprisingly, overexpression of CUC1 was sufficient to induce adventitious shoots on the adaxial surface of cotyledons. Expression analyses in the overexpressor and in loss-of-function mutants suggest that CUC1 acts upstream of the SHOOT MERISTEMLESS gene.

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The Populus homeobox gene ARBORKNOX1 reveals overlapping mechanisms regulating the shoot apical meristem and the vascular cambium

Plant Molecular Biology ◽

10.1007/s11103-006-0059-y ◽

2006 ◽

Vol 61 (6) ◽

pp. 917-932 ◽

Cited By ~ 90

Author(s):

Andrew T. Groover ◽

Shawn D. Mansfield ◽

Stephen P. DiFazio ◽

Gayle Dupper ◽

Joseph R. Fontana ◽

...

Keyword(s):

Shoot Apical Meristem ◽

Apical Meristem ◽

Homeobox Gene ◽

Vascular Cambium

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How repeated epiphylly correlates with gene expression of resident knox1 in the leaves of tobacco epiphyllous shoots

Open Life Sciences ◽

10.2478/s11535-006-0012-8 ◽

2006 ◽

Vol 1 (2) ◽

pp. 263-274 ◽

Cited By ~ 1

Author(s):

Kai Müller ◽

Jinxing Lin ◽

Rainer Fischer ◽

Dirk Prüfer

Keyword(s):

Gene Expression ◽

Transgenic Plant ◽

Shoot Apical Meristem ◽

Plant Material ◽

Apical Meristem ◽

Leaf Primordia ◽

Wild Type ◽

Expression Domain ◽

Enhanced Expression ◽

Founder Cells

AbstractThe tobacco knox1 genes tokn1 and tokn2 were isolated and their neomorphic capacities were tested while expressed in tobacco and potato. In addition, their neomorphic capacities were compared to barley bkn3 transgenic plant material. While tokn2 and bkn3 induced epiphylly in tobacco and supercompound leaves in potato, tokn1 failed to produce such prominent knox1 specific phenotypes. In wild type tobacco, alleles of the tokn genes were found to be expressed within distinct zones of the shoot apical meristem (SAM), leaving out regions that correlated with leaf founder cells [1]. In contrast, the expression of the tokn genes was detected throughout the meristem and in leaf primordia of epiphyllous shoots that developed in tobacco over-expressing the barley hooded gene bkn3. It was determined that such extended expression domains of resident tobacco knox1 genes were mediated through an enhanced expression domain of bkn3 within the tissue confined to the epiphylls, and this contributed to “repeated epiphylly”, i.e. an iterated development of epiphyllous shoots on leaves of progenitor epiphylls.

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In situ localization of storage protein mRNAs in developing meristems of Brassica napus embryos

Development ◽

10.1242/dev.111.2.299 ◽

1991 ◽

Vol 111 (2) ◽

pp. 299-313 ◽

Cited By ~ 1

Author(s):

D.E. Fernandez ◽

F.R. Turner ◽

M.L. Crouch

Keyword(s):

Brassica Napus ◽

Storage Protein ◽

Shoot Apical Meristem ◽

Apical Meristem ◽

Vascular Tissue ◽

Leaf Primordia ◽

Root Apical Meristem ◽

Cdna Clones ◽

Final Maturation

Probes derived from cDNA clones of napin and cruciferin, the major storage proteins of Brassica napus, and in situ hybridization techniques were used to examine changes in the spatial and temporal distribution of storage protein messages during the course of embryogeny, with a special emphasis on the developing apical meristems. Napin mRNAs begin to accumulate in the cortex of the axis during late heart stage, in the outer faces of the cotyledons during torpedo stage and in the inner faces of the cotyledons during cotyledon stage. Cruciferin mRNAs accumulate in a similar pattern but approximately 5 days later. Cells in the apical regions where root and shoot meristems develop do not accumulate storage protein messages during early stages of embryogeny. In the upper axis, the boundary between these apical cells and immediately adjacent cells that accumulate napin and cruciferin mRNAs is particularly distinct. Our analysis indicates that this boundary is not related to differences in tissue or cell type, but appears instead to be coincident with the site of a particular set of early cell divisions. A major change in the mRNA accumulation patterns occurs halfway through embryogeny, as the embryos enter maturation stage and start drying down. Final maturation of the shoot apical meristem is associated with the development of leaf primordia and the accumulation of napin mRNAs in the meristem, associated leaf primordia and vascular tissue. Cruciferin mRNAs accumulate only in certain zones of the shoot apical meristem and on the flanks of leaf primordia. Neither type of mRNA accumulates in the root apical meristem at any stage.

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Expression of maize KNOTTED1 related homeobox genes in the shoot apical meristem predicts patterns of morphogenesis in the vegetative shoot

Development ◽

10.1242/dev.120.2.405 ◽

1994 ◽

Vol 120 (2) ◽

pp. 405-413 ◽

Cited By ~ 32

Author(s):

D. Jackson ◽

B. Veit ◽

S. Hake

Keyword(s):

Shoot Apical Meristem ◽

Leaf Development ◽

Apical Meristem ◽

Expression Patterns ◽

Homeobox Genes ◽

Homeobox Gene ◽

Vegetative Shoot ◽

Lateral Organs ◽

Floral Meristems ◽

Shoot Meristems

In this paper we describe the expression patterns of a family of homeobox genes in maize and their relationship to organogenic domains in the vegetative shoot apical meristem. These genes are related by sequence to KNOTTED1, a gene characterized by dominant neomorphic mutations which perturb specific aspects of maize leaf development. Four members of this gene family are expressed in shoot meristems and the developing stem, but not in determinate lateral organs such as leaves or floral organs. The genes show distinct expression patterns in the vegetative shoot apical meristem that together predict the site of leaf initiation and the basal limit of the vegetative ‘phytomer’ or segmentation unit of the shoot. These genes are also expressed in the inflorescence and floral meristems, where their patterns of expression are more similar, and they are not expressed in root apical meristems. These findings are discussed in relation to other studies of shoot apical meristem organization as well as possible commonality of homeobox gene function in the animal and plant kingdoms.

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Shoot meristem size is dependent on inbred background and presence of the maize homeobox gene, knotted1

Development ◽

10.1242/dev.127.14.3161 ◽

2000 ◽

Vol 127 (14) ◽

pp. 3161-3172 ◽

Cited By ~ 3

Author(s):

E. Vollbrecht ◽

L. Reiser ◽

S. Hake

Keyword(s):

Gene Function ◽

Apical Meristem ◽

Homeobox Gene ◽

Shoot Meristem ◽

Dominant Allele ◽

Element Analysis ◽

Meristem Size ◽

Recessive Mutations ◽

Undifferentiated State ◽

Meristem Maintenance

The knotted1 (kn1) gene of maize is expressed in meristems and is absent from leaves, including the site of leaf initiation within the meristem. Recessive mutations of kn1 have been described that limit the capacity to make branches and result in extra carpels. Dominant mutations suggest that kn1 function plays a role in maintaining cells in an undifferentiated state. We took advantage of a Ds-induced dominant allele in order to screen for additional recessive alleles resulting from mobilization of the Ds element. Analysis of one such allele revealed a novel embryonic shoot phenotype in which the shoot initiated zero to few organs after the cotyledon was made, resulting in plants that arrested as seedlings. We refer to this phenotype as a limited shoot. The limited shoot phenotype reflected loss of kn1 function, but its penetrance was background dependent. We examined meristem size and found that plants lacking kn1 function had shorter meristems than non-mutant siblings. Furthermore, meristems of restrictive inbreds were significantly shorter than meristems of permissive inbreds, implying a correlation between meristem height and kn1 gene function in the embryo. Analysis of limited shoot plants during embryogenesis indicated a role for kn1 in shoot meristem maintenance. We discuss a model for kn1 in maintenance of the morphogenetic zone of the shoot apical meristem.

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