Abstract
Rice panicle architecture is one of the most important morphological traits specifying rice yield potential, which was under selection during rice domestication. A panicle is a branched structure composed of a rachis, primary branches, higher order branches (i.e. secondary and tertiary branches) and finally spikelets. This morphology, depending on the activity of axillary meristems during its development, shows a wide diversity in both inter-specific (i.e. crops vs. wild-relatives) and intra-specific (Asian or/and African rice) levels. Several important genes/QTLs have been characterized in Oryza sativa as controlling panicle architecture by regulating meristem fate, cell division and hormone signaling. However the mechanisms related to rice panicle diversity and its evolution in the context of domestication are still largely unknown. During my PhD, I mainly investigated the histological and molecular bases of panicle diversity between the African species Oryza glaberrima and its wild-relative Oryza barthii. I analyzed the expression patterns of orthologs of O. sativa landmark genes related to panicle development and was involved in small RNA transcriptomic analysis in early stages of panicle development. This work revealed a high conservation of the spatial expression pattern of the landmarks genes studied but have highlighted a differential timing and level of the expression of these genes during the panicle development between two species. The genes promoting meristem activity were upper-accumulated over a longer period during the panicle development in the crop species, whereas the gene promoting spikelet/floret meristem fate behaved in opposite way. This work also has shown similar heterochronic alteration of the expression of members of the miR2118-triggered 21-nt phased siRNA pathway, known to be involved in male gametogenesis. Together, these findings suggest that variation of panicle complexity in African rice may rely on heterochronic changes in branching activity as well as spikelet/floret meristem determinacy.