RESUMEN
The process of L1 specification early in plant embryogenesis, and subsequent maintenance and elaboration of epidermal organization, are fundamental to plant growth and fitness. To occur in a co-ordinated fashion, these processes require considerable cell-cell cross-talk. It is perhaps then unsurprising that several classes of plant RLKs (receptor-like kinases), as well as other membrane-localized signalling components, have been implicated both in epidermal specification and in patterning events governing the distribution of epidermal cell types. However, despite our growing knowledge of the roles of these signalling molecules, remarkably little is understood regarding their function at the cellular level. In particular the potential role of regulated proteolytic cleavage in controlling the activity of signalling molecules at the plant plasma membrane has remained largely unaddressed despite its massive importance in signalling in animal systems. Because of the relative physical accessibility of their expression domains, molecules involved in epidermal development present opportunities for investigating mechanisms of cell-cell signalling in planta. Advances in understanding the potential regulatory processing of membrane-localized signalling molecules during epidermal development will be examined using parallels with animal systems to highlight potential future directions for this field of research.
Asunto(s)
Arabidopsis/embriología , Arabidopsis/fisiología , Regulación de la Expresión Génica de las Plantas , Epidermis de la Planta/metabolismo , Transducción de Señal , Comunicación Celular , Ciclo Celular , Linaje de la Célula , Ligandos , Modelos Biológicos , Fenómenos Fisiológicos de las PlantasRESUMEN
A family of homeo box genes with cell layer-specific expression patterns defining subdomains of the embryo and certain meristems has been isolated from maize. These genes encode proteins from the class of plant specific homeo domain-leucine zipper (HD-Zip) transcription factors containing the previously described ZmOCL1 protein, and have been designated ZmOCL2, ZmOCL3, ZmOCL4 and ZmOCL5. ZmOCL3, ZmOCL4 and ZmOCL5, like ZmOCL1, showed essentially L1 or epidermis-specific expression. However, each gene was expressed in a distinct region of the embryonic protoderm during early development, with ZmOCL3 showing suspensor-specific expression, ZmOCL4 transcripts being localized to the adaxial face of the embryo proper and ZmOCL5 showing a more abaxial expression pattern. All three genes were also expressed in vegetative, inflorescence and floral apices, although ZmOCL3 transcripts were excluded from meristems and very young organ primordia. In contrast, ZmOCL2 expression was entirely meristem-specific and was excluded from the L1 layer, appearing instead to be largely restricted to a cell layer directly beneath the L1, especially in floral meristems. This expression pattern is unprecedented and may indicate that cell-layer organization in maize meristems is more complex than that suggested by the classical L1/L2 (outer cell layer/inner cell mass) model. These differing expression patterns indicate that the members of the HD-ZipIV family of maize may not only play roles in defining different regions of the epidermis during embryonic development, but could also be responsible for maintaining cell-layer identity in meristematic regions.
Asunto(s)
Regulación de la Expresión Génica de las Plantas , Proteínas de Homeodominio/genética , Semillas/genética , Zea mays/genética , Secuencia de Aminoácidos , Secuencia de Bases , Cartilla de ADN , ADN Complementario , Datos de Secuencia Molecular , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Homología de Secuencia de Aminoácido , Zea mays/embriologíaRESUMEN
The formation of a morphologically distinct outer cell layer or protoderm is one of the first and probably one of the most important steps in patterning of the plant embryo. Here we report the isolation of ZmOCL1 (OCL for outer cell layer), a member of the HDGL2 (also known as HD-ZIP IV) subclass of plant-specific HD-ZIP homeodomain proteins from maize. ZmOCL1 transcripts are detected very early in embryo development, before a morphologically distinct protoderm is visible, and expression then becomes localised to the protoderm of the embryo as it develops. Subsequently, expression is observed in the L1 cell layer of both the developing primary root and shoot meristems, and is maintained in developing leaves and floral organs. We propose that ZMOCL1 may play a role in the specification of protoderm identity within the embryo, the organisation of the primary root primordium or in the maintenance of the L1 cell layer in the shoot apical meristem. We also show that the expression of ZmOCL1 is different from that of another epidermal marker gene, LTP2 (lipid transfer protein) and, in meristems, is complementary to that of Kn1 (Knotted) which is transcribed only in underlying cell layers.
Asunto(s)
Genes Homeobox/genética , Genes de Plantas/genética , Proteínas de la Membrana/genética , Proteínas de Plantas/genética , Semillas/genética , Zea mays/genética , Secuencia de Aminoácidos , ADN Complementario/química , ADN Complementario/genética , ADN de Plantas/química , ADN de Plantas/genética , Regulación del Desarrollo de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Hibridación in Situ , Datos de Secuencia Molecular , ARN Mensajero/genética , ARN Mensajero/metabolismo , Semillas/crecimiento & desarrollo , Alineación de Secuencia , Análisis de Secuencia de ADN , Homología de Secuencia de Aminoácido , Distribución Tisular , Zea mays/embriología , Zea mays/crecimiento & desarrolloRESUMEN
Small GTPases have diverse roles in animals and yeast, including signal transduction, regulation of secretion, organisation of the cytoskeleton, and control of cell division. Similar GTPases have also been found in bacteria, such as the Escherichia coli GTPase ERA, which is involved in regulating metabolism and cell division [1,2]. Many small GTPases have been cloned from plants but their functional analysis has largely been limited to complementation of mutations in corresponding yeast genes, and antisense experiments which have implicated these proteins in processes such as root nodulation [3,4]. No mutations in plant GTPases have been reported, and thus their true importance in plant growth and development is unknown. Here we report the isolation of a gene from Antirrhinum majus encoding a protein from an entirely novel class of eukaryotic GTPases showing strongest similarity to the prokaryotic protein ERA. We have named this gene ERG (for ERA-related GTPase). The ERG gene is expressed in dividing or metabolically active cells. We generated a deletion allele of ERG by site-selected transposon mutagenesis and have shown that seeds containing embryos and endosperm homozygous for this deletion arrest soon after fertilisation. We conclude that ERG has a crucial role in plant growth and development, possibly by influencing mitochondrial division.
Asunto(s)
GTP Fosfohidrolasas/genética , Genes de Plantas , Proteínas de Plantas/genética , Plantas/genética , Secuencia de Aminoácidos , Proteínas Bacterianas/química , Secuencia de Bases , Escherichia coli/enzimología , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Plantas/embriología , Semillas/embriología , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Especificidad de la EspecieRESUMEN
The fimbriata (fim) gene of Antirrhinum affects both the identity and arrangement of organs within the flower, and encodes a protein with an F-box motif. We show that FIM associates with a family of proteins, termed FAPs (FIM-associated proteins), that are closely related to human and yeast Skp1 proteins. These proteins form complexes with F-box-containing partners to promote protein degradation and cell cycle progression. The fap genes are expressed in inflorescence and floral meristems in a pattern that incorporates the domain of fim expression, supporting an in vivo role for a FIM-FAP complex. Analysis of a series of novel fim alleles shows that fim plays a key role in the activation of organ identity genes. In addition, fim acts in the regions between floral organs to specify the correct positioning and maintenance of morphological boundaries. Taking these results together, we propose that FIM-FAP complexes affect both gene expression and cell division, perhaps by promoting selective degradation of regulatory proteins. This may provide a mechanism by which morphological boundaries can be aligned with domains of gene expression during floral development.
Asunto(s)
Regulación de la Expresión Génica de las Plantas , Genes Homeobox , Genes de Plantas , Proteínas de Plantas/fisiología , Plantas/genética , Secuencia de Aminoácidos , Secuencia de Bases , Proteína DEFICIENS , Proteínas de Homeodominio/biosíntesis , Proteínas de Homeodominio/genética , Humanos , Datos de Secuencia Molecular , Morfogénesis/genética , Mosaicismo , Mutagénesis Sitio-Dirigida , Especificidad de Órganos , Proteínas de Plantas/genética , Saccharomyces cerevisiae/genética , Alineación de Secuencia , Homología de Secuencia , Especificidad de la EspecieRESUMEN
The unusual floral organs (ufo) mutant of Arabidopsis has flowers with variable homeotic organ transformations and inflorescence-like characteristics. To determine the relationship between UFO and previously characterized meristem and organ identity genes, we cloned UFO and determined its expression pattern. The UFO gene shows extensive homology with FIMBRIATA (FIM), a gene mediating between meristem and organ identity genes in Antirrhinum. All three UFO mutant alleles that we sequenced are predicted to produce truncated proteins. UFO transcripts were first detected in early floral meristems, before organ identity genes had been activated. At later developmental stages, UFO expression is restricted to the junction between sepal and petal primordia. Phenotypic, genetic, and expression pattern comparisons between UFO and FIM suggest that they are cognate homologs and play a similar role in mediating between meristem and organ identity genes. However, some differences in the functions and genetic interactions of UFO and FIM were apparent, indicating that changes in partially redundant pathways have occurred during the evolutionary divergence of Arabidopsis and Antirrhinum.