GNP6, a novel allele of MOC1, regulates panicle and tiller development in rice

The yield of rice is mostly affected by three factors, namely, panicle number, grain number and grain weight. Variation in panicle and grain numbers is mainly caused by tiller and panicle branches generated from axillary meristems (AMs). MOC1 encodes a putative GRAS family nuclear protein that regulates AM formation. Although several alleles of MOC1 have been identified, its variation in germplasm resources remains unclear. In the present study we characterized a novel moc1 allele named gnp6 which has a thymine insertion in the coding sequence of the SAW motif in the GRAS domain. This mutation causes arrested branch formation. The SAW motif is necessary for nuclear localization of GNP6/MOC1 where it functions as a transcription factor or co-regulator. Haplotype analysis showed that the coding region of GNP6/MOC1 was conserved without any non-synonymous mutations in 240 rice accessions. However, variation in the promoter region might affect the expression of it and its downstream genes. Joint haplotype analysis of GNP6/MOC1 and MOC3 showed that haplotype combinations H9, H10 and H11, namely MOC1-Hap1 in combination with MOC3-Hap3, MOC3-Hap4 or MOC3-Hap5 could be bred to promote branch formation. These findings will enrich the genetic resources available for rice breeders.