IDENTIFICATION AND FUNCTIONAL CHARACTERIZATION OF GENES CONTROLLING REPRODUCTIVE MERISTEMS DEVELOPMENT IN THE MODEL SPECIES RICE (ORYZA SAT/VA)

Meristems are groups of pluripotent cells that contribute to plant growth and the development of its organs. In rice the inflorescence architecture, which determines the grain yield is established at early stages of reproductive development. Activity of the different types of reproductive meristem and the timing of transition between them shape the branching pattern and the number of spikelets on the inflorescence. A few genes that specify the identity of these meristems and regulate the transitions have been reported but the molecular mechanisms, underlying this process are still not clear. To gain a better understanding we used a precise laser microdissection and RNA-sequencing approach in Oryza sativa ssp. japonica cv. Nipponbare to elucidate the landscape of gene expression in four reproductive meristem types: the rachis meristem (RM), the primary branch meristem (PBM), the elongating primary branch meristem (including axillary meristems) (ePBM/AM), and the spikelet meristem (SM). We found that genes could be grouped based on specific expression behavior in these meristem types. The bioinformatics analysis of the datasets resulted in the identification of several genes potentially involved in branching. We generated loss of function mutants using a genome editing CRISPR/Cas9 approach, for two promising candidate genes, namely G1L1 and G1L2, both belonging to the ALOG family encoding a conserved domain: \u201cDomain of Unknown Function 640\u201d (DUF640). The knock-outs revealed an interesting branching phenotype that is consistent with the expression profile of these genes. Future research of our datasets combined with mutant analysis are expected to provide important new insights into the molecular mechanism that control rice inflorescence development, which has as an ultimate scope the improvement of grain yield, a trait that has without any doubt top priority for a sustainable agriculture of the future