ABSTRACT
Interactions between TALE (three-amino acid loop extension) homeodomain proteins play important roles in the development of both fungi and animals. Although in plants, two different subclasses of TALE proteins include important developmental regulators, the existence of interactions between plant TALE proteins has remained unexplored. We have used the yeast two-hybrid system to demonstrate that the Arabidopsis BELL1 (BEL1) homeodomain protein can selectively heterodimerize with specific KNAT homeodomain proteins. Interaction is mediated by BEL1 sequences N terminal to the homeodomain and KNAT sequences including the MEINOX domain. These findings validate the hypothesis that the MEINOX domain has been conserved between plants and animals as an interaction domain for developmental regulators. In yeast, BEL1 and KNAT proteins can activate transcription only as a heterodimeric complex, suggesting a role for such complexes in planta. Finally, overlapping patterns of BEL1 and SHOOT MERISTEMLESS (STM) expression within the inflorescence meristem suggest a role for the BEL1-STM complex in maintaining the indeterminacy of the inflorescence meristem.
Subject(s)
Arabidopsis/genetics , Homeodomain Proteins/genetics , Plant Proteins , Transcription Factors/genetics , Arabidopsis Proteins , Base Sequence , Conserved Sequence , DNA Primers , Gene Library , Homeodomain Proteins/chemistry , Homeodomain Proteins/metabolism , In Situ Hybridization , Molecular Sequence Data , Polymerase Chain Reaction , Saccharomyces cerevisiae/genetics , Transcription Factors/chemistryABSTRACT
MADS-domain-containing transcription factors play diverse roles in plant development. The prototypic members of this gene family are the floral organ identity genes of the model dicotyledonous plant, Arabidopsis thaliana. Sequence relatedness and function ascribe them to AP1/AGL9, AG, AP3 and PI gene groups. The rice MADS-box gene, OsMADS1, is a member of the AP1/ AGL9 sub-group. Tomato and Petunia members of this sub-group specify floral meristem identity and control organ development in three inner whorls. Reported here are phylogenetic analyses that show OsMADS1 to form a distinct clade within the AGL9 gene family. This sub-group currently has only three other monocot genes. We have studied the expression pattern of OsMADS1 and determined the consequences of its ectopic expression in transgenic rice plants. OsMADS1 is not expressed during panicle branching; earliest expression is in spikelet meristems where it is excluded from the outer rudimentary/sterile glumes. During organogenesis, OsMADS1 expression is confined to the lemma and palea, with weak expression in the carpel. Ectopic OsMADS1 expression results in stunted panicles with irregularly positioned branches and spikelets. Additionally, in spikelets, the outer rudimentary glumes are transformed to lemma/palea-like organs. Together, these data suggest a distinct role for OsMADS1 and its monocot relatives in assigning lemma/palea identity.
Subject(s)
Oryza/genetics , Plant Physiological Phenomena , Poaceae/genetics , Transcription Factors/biosynthesis , Transcription Factors/genetics , Alleles , DNA, Complementary/metabolism , Databases as Topic , Gene Expression Regulation, Plant , In Situ Hybridization , Solanum lycopersicum/classification , Solanum lycopersicum/genetics , MADS Domain Proteins , Microscopy, Electron, Scanning , Oryza/classification , Phenotype , Phylogeny , Plant Proteins , Poaceae/classification , RNA/metabolism , Reverse Transcriptase Polymerase Chain Reaction , TransgenesABSTRACT
Studies of floral organ development in two dicotyledonous plants, Arabidopsis thaliana and Antirrhinum majus, have shown that three sets of genes (A, B and C) can pattern sepals, petals, stamens and carpels [1] [2]. Mechanisms that define boundaries between these floral whorls are unclear, however. The Arabidopsis gene SUPERMAN (SUP), which encodes a putative transcription factor, maintains the boundary between stamens and carpels [3] [4] [5], possibly by regulating cell proliferation. By overexpressing SUP cDNA in rice, we examined whether its effects on whorl boundaries are conserved in a divergent monocotyledonous species. High-level ectopic SUP expression in transgenic rice resulted in juvenile death or dwarf plants with decreased axillary growth. Plants with lower levels of SUP RNA were vegetatively normal, but the flowers showed ubiquitous ventral carpel expansion. This was often coupled with reduced stamen number, or occurrence of third-whorl stamen-carpel mosaic organs. Additionally, proliferation of second-whorl ventral cells produced adventitious lodicules, and flowers lost the asymmetry that is normally inherent to this whorl. We predict that SUP is a conserved regulator of floral whorl boundaries and that it affects cell proliferation.
