Using Plant Genetic Resources to Understand the Developmental Genetic Basis of Grass Morphological Diversity.

Model organisms such as Arabidopsis, corn, and rice provide testable hypotheses of how genes have regulated the evolution of morphological forms within plants. We can test these hypotheses by combining developmental, gene expression and molecular evolutionary analyses of diverse plant species within an explicit phylogenetic framework. Corn BARREN STALK1 (ZmBA1) and rice LAX PANICLE (OsLAX) genes regulate inflorescence branching by controlling auxin transport, but the extent to which they perform similar roles in other crops is unknown. Phylogenetic analyses indicate that the BA1/LAX clade resulted from a gene duplication event within monocots. Expression analyses in barley and sorghum support the hypothesis that BA1/LAX genes regulate inflorescence branching in the bulk of grass species. The origin of the BA1/LAX clade within monocots suggests these genes might also regulate inflorescence branching in diverse monocot crops. Based on functional analyses in rice, the SEPALLATA gene LEAFY HULL STERILE1 (LHS1) has been linked to both the origin of lemmas within grass flowers and the diversification of the grass spikelet. Phylogenetic analyses indicate that LHS1 and its paralog Oryza sativa MADS5 (OsMADS5) resulted from a gene duplication event at the base of the grass family. LHS1 expression has been detected in lemmas of all grasses tested to date supporting it's role in the development of this structure, but LHS1 expression patterns in grasses are not conserved pointing to additional developmental roles during spikelet development. Analyses in Joinvillea (a close relative of grasses) reveal expression of the LHS1/OsMADS5 precursor in both tepal whorls and in the stamen filament, pointing to potential partitioning of gene function in grasses following the LHS1/OsMADS5 duplication event. Together these analyses show the utility of testing hypotheses derived from model species in non-model species and offer a framework to identify strategies of improving crop yield in diverse species.