A Novel Variation in the FRIZZLE PANICLE (FZP) Gene Promoter Improves Grain Number and Yield in Rice.

Secondary branch number per panicle plays a crucial role in regulating grain number and yield in rice. Here we report the positional cloning and functional characterization for SECONDARY BRANCH NUMBER7 (qSBN7), a quantitative trait locus affecting secondary branch per panicle and grain number. Our research revealed that the causative variants of qSBN7 are located in the distal promoter region of FRIZZLE PANICLE (FZP), a gene previously associated with repression of axillary meristem development in rice spikelets. qSBN7 is a novel allele of FZP which causes an approximately 56% decrease in its transcriptional level, leading to increased secondary branch and grain number, and reduced grain length. Field evaluations showed that qSBN7 increased grain yield by 10.9% in a temperatejaponica variety, TN13, likely due to its positive effect on sink capacity. Our findings suggest that incorporation of qSBN7 can increase yield potential and improve the breeding of elite rice varieties.