Poster: Vegetative development

Abs # 314: RAM, a myb-related transcription factor co-regulates branching and flowering time in Arabidopsis thaliana

Presenter:	Keller, Thomas , Thomas.Keller@ed.ac.uk
Authors	Keller, Thomas  (A)   Doerner, Peter  (A)
Affiliations:	(A): Institute of Cell and Molecular Biology, University of Edinburgh, Scotland, UK

Branches and flowers both originate from axillary meristems (AMs). We have identified activation-tagged, gain-of-function (ram-d) [ram = regulator of axillary meristems], and T-DNA tagged, loss-of-function (ram-ko) alleles of a myb-related transcription factor that exhibit AM defects resulting in altered branching and flowering time phenotypes. Supernumerary and mis-positioned AMs are initiated, but not maintained in ram-d leaf axils resulting in a lack of rosette paraclades. ram-d plants additionally exhibit phenotypes reminiscent of gibberellin (GA) deficient mutants including delayed flowering, extended vegetative phase, dwarfism and dark green coloration. In contrast, ram-ko mutant plants flower earlier with less vegetative leaves reminiscent of GA-accumulating mutants and are defective in AM formation leading to barren leaf axils and a significant reduction in rosette and cauline paraclades. RAM mRNA is only abundant in apices, but not in leaves of wild-type plants. Consistent with a function in AM regulation, in-situ hybridization as well as RAM promoter::GUS reporter lines indicate strongest RAM expression on the adaxial surface of young leaf primordia, primarily at their base, the position of the future AMs. Microarray data suggest stem cell niche genes and genes regulating GA biosynthesis as possible targets of RAM. The late-flowering phenotype of ram-d is completely rescued by exogenous GA application. We propose that RAM couples the control of branching and flowering time by regulating the efficient formation or maintenance of stem cell niches in leaf axils in a GA-dependent manner. Therefore, this gene activity is an important determinant of competitive success by regulating fecundity and the balance of vegetative and reproductive development.