Duplication, conservation and diversification of MADS-box transcription factors involved in grass inflorescence and floral development

In Arabidopsis a subclass of MADS-box genes, the APETALA1/FRUITFULL (AP1/FUL) genes, are involved in meristem identity, and floral organ identity, establishing these genes as potential candidates for the evolution of inflorescence form in other angiosperms. Little is known about their evolutionary history or developmental function outside core eudicots. I investigated the evolutionary history of AP1/FUL-like gene in Poaceae, to test functional hypotheses regarding the role of both genes in inflorescence and floral development.; In chapter one I reconstruct the evolutionary history of grass AP1/FUL genes FUL1 and FUL2. The duplication event giving rise to FUL1 and FUL2 occurred at the base of Poaceae and codon substitutions occurred under relaxed selection mostly along the branch leading to FUL2. Following gene duplication, FUL1 was lost from early-diverging taxa, a pattern consistent with major changes in grass floral morphology. In chapter two I analyze the expression of FUL1 and FUL2 across distantly related grasses to test hypotheses of gene function. FUL1 has a wider expression pattern in all spikelet organs than FUL2, but both genes are expressed throughout spikelet organs of some cereals. Together, these data support a redundant role for grass AP1/FUL genes in spikelet merstem identity, a general role for FUL1 in floral organ identity, and a more specific role for FUL2 in outer floral whorl identity. I hypothesize that subfunctionalization of FUL2 and interaction of FUL2 with LHS1 could specify lemma and palea identity in the grass floret.; Finally, in chapter three, I determine FUL1 and FUL2 expression profiles for different growth habits of oat ( Avena saliva) and wheat (Triticum monococcum ) with cold treatment to determine the role of AP1/FUL genes in flowering time. Results demonstrate significant up-regulation of FUL1 expression in leaves of winter oat and wheat in response to vernalization, followed by later up-regulation in the shoot apical meristem. These data suggest distinct roles for cereal grass AP1/FUL genes in systemic signaling to induce flowering competency, and in meristematic tissues to activate genes involved in the transition to flowering. Furthermore, they support the hypothesis that FUL1 is a common regulator of vernalization responsiveness, at least within the crown pooids.