Abstract
Rice is a staple food for more than half of the world's population. The goal of increasing or sustainably maintaining rice production in a context of climate change and decreasing water and arable land availability requires the establishment of high-yield plants in contrasting environments. Rice yield is a complex trait, governed by genetic and epigenetic factors. It is directly dependent on 3 related traits: the number of panicles per plant, the number of grains per panicle and grain weight. During rice domestications in Asia and Africa, grain number was one of the main traits under selection, resulting in a phenotypic convergence between the crop plants that emerged on the two continents in relation to their yield potential. Panicle development in Oryza sativa has been well documented but the evolution of panicle architecture from the wild to the cultivated form remains poorly studied, especially with regard to the underlying molecular regulatory processes. To address this issue, two different transcriptomic resources were developed in the host laboratory. The first involved a comparison between the transcriptomes of different panicle meristem types in O. sativa. The second was a study of gene expression during panicle branch initiation in Asian and African cultivated species (O. sativa and Oryza glaberrima) with respect to their wild relatives (Oryza rufipogon and Oryza barthii, respectively). The two sets of genes thus identified displayed a significant enrichment in AP2/ERF family genes. Eighty four of the 170 AP2/ERF genes reported in O. sativa from the different sub-families (DREB, RAV, AP2 and Soloist) are expressed in the panicle and some are differentially expressed between the different types of meristems or stages of development and/or species. The euANT/PLT group within the AP2 subfamily comprises 4 genes (OsPLT7, OsPLT8, OsPLT9 and AP2/EREBP22) that are of particular interest in the context of the control of panicle development and architectural diversity between wild and cultivated species. A functional analysis of these 4 genes in the same genetic background was initiated by CRISPR-Cas9 approaches in O. sativa cv Kitaake. The results obtained revealed an effect of induced mutations on panicle architecture (number of primary and secondary branches) and/or on the size of the panicle (length of the branches and internodes).