Differences in meristem size and expression of branching genes are associated with variation in panicle phenotype in wild and domesticated African rice.

Background: The African rice was domesticated from its wild relative about 3000 years ago. During the domestication process, panicle complexity changed from a panicle with low complexity in , to a highly branched panicle carrying more seeds in . To understand the basis of this differential panicle development between the two species, we conducted morphological and molecular analyses of early panicle development.

Results: Using X-ray tomography, we analyzed the morphological basis of early developmental stages of panicle development. We uncovered evidence for a wider rachis meristem in than in . At the molecular level, spatial and temporal expression profiles of orthologs of genes related to meristem activity and meristem fate control were obtained using in situ hybridization and qRT-PCR. Despite highly conserved spatial expression patterns between and , differences in the expression levels of these early acting genes were detected.

Conclusion: The higher complexity of the panicle compared to that of its wild relative is associated with a wider rachis meristem and a modification of expression of branching-related genes. Our study indicates that the expression of genes in the // and pathways, along with that of their target genes, is altered from the unbranched stage of development. This suggests that differences in panicle complexity between the two African rice species result from early alterations to gene expression during reproductive development.