RESUMO
The ABC model of flower organ identity is widely recognized as providing a framework for understanding the specification of flower organs in diverse plant species. Recent studies in Arabidopsis thaliana have shown that three closely related MADS-box genes, SEPALLATA1 (SEP1), SEP2 and SEP3, are required to specify petals, stamens, and carpels because these organs are converted into sepals in sep1 sep2 sep3 triple mutants. Additional studies indicate that the SEP proteins form multimeric complexes with the products of the B and C organ identity genes. Here, we characterize the SEP4 gene, which shares extensive sequence similarity to and an overlapping expression pattern with the other SEP genes. Although sep4 single mutants display a phenotype similar to that of wild-type plants, we find that floral organs are converted into leaf-like organs in sep1 sep2 sep3 sep4 quadruple mutants, indicating the involvement of all four SEP genes in the development of sepals. We also find that SEP4 contributes to the development of petals, stamens, and carpels in addition to sepals and that it plays an important role in meristem identity. These and other data demonstrate that the SEP genes play central roles in flower meristem identity and organ identity.
Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Flores/genética , Regulação da Expressão Gênica de Plantas , Meristema/genética , Mutação/genética , Organogênese/genética , Sequência de Aminoácidos , Arabidopsis/anatomia & histologia , Proteínas de Arabidopsis/metabolismo , Flores/ultraestrutura , Genótipo , Hibridização In Situ , Microscopia Eletrônica de Varredura , Dados de Sequência Molecular , Oligonucleotídeos , Alinhamento de Sequência , Análise de Sequência de DNARESUMO
The AGAMOUS (AG) gene is necessary for stamen and carpel development and is part of a monophyletic clade of MADS-box genes that also includes SHATTERPROOF1 (SHP1), SHP2, and SEEDSTICK (STK). Here, we show that ectopic expression of either the STK or SHP gene is sufficient to induce the transformation of sepals into carpeloid organs bearing ovules. Moreover, the fact that these organ transformations occur when the STK gene is expressed ectopically in ag mutants shows that STK can promote carpel development in the absence of AG activity. We also show that STK, AG, SHP1, and SHP2 can form multimeric complexes and that these interactions require the SEPALLATA (SEP) MADS-box proteins. We provide genetic evidence for this role of the SEP proteins by showing that a reduction in SEP activity leads to the loss of normal ovule development, similar to what occurs in stk shp1 shp2 triple mutants. Together, these results indicate that the SEP proteins, which are known to form multimeric complexes in the control of flower organ identity, also form complexes to control normal ovule development.
Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Flores/crescimento & desenvolvimento , Proteínas de Domínio MADS/genética , Sementes/crescimento & desenvolvimento , Proteína AGAMOUS de Arabidopsis/genética , Proteína AGAMOUS de Arabidopsis/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Flores/genética , Flores/ultraestrutura , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Proteínas de Domínio MADS/metabolismo , Microscopia Eletrônica de Varredura , Mutação , Plantas Geneticamente Modificadas , Sementes/genética , Sementes/ultraestrutura , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
Carpels are essential for sexual plant reproduction because they house the ovules and subsequently develop into fruits that protect, nourish and ultimately disperse the seeds. The AGAMOUS (AG) gene is necessary for plant sexual reproduction because stamens and carpels are absent from ag mutant flowers. However, the fact that sepals are converted into carpelloid organs in certain mutant backgrounds even in the absence of AG activity indicates that an AG-independent carpel-development pathway exists. AG is a member of a monophyletic clade of MADS-box genes that includes SHATTERPROOF1 (SHP1), SHP2 and SEEDSTICK (STK), indicating that these four genes might share partly redundant activities. Here we show that the SHP genes are responsible for AG-independent carpel development. We also show that the STK gene is required for normal development of the funiculus, an umbilical-cord-like structure that connects the developing seed to the fruit, and for dispersal of the seeds when the fruit matures. We further show that all four members of the AG clade are required for specifying the identity of ovules, the landmark invention during the course of vascular plant evolution that enabled seed plants to become the most successful group of land plants.