Identification of genomic regions controlling spikelet degeneration under FRIZZLE PANICLE (FZP) defect genetic...

The FZP gene plays a critical role in the formation of lateral branches and spikelets in rice panicle architecture. This study investigates the qSBN7 allele, a hypomorphic variant of FZP, and its influence on panicle architectures in different genetic backgrounds. We evaluated two backcross inbred lines (BILs), BC5_TCS10^sbn and BC3_TCS10^sbn, each possessing the homozygous qSBN7 allele but demonstrating differing degrees of spikelet degeneration. Our analysis revealed that BC5_TCS10^sbn had markedly low FZP expression, which corresponded with an increase in axillary branches and severe spikelet degeneration. Conversely, BC3_TCS10^sbn exhibited significantly elevated FZP expression, leading to fewer secondary and tertiary branches, and consequently decreased spikelet degeneration. Compared to BC5_TCS10^sbn, BC3_TCS10^sbn carries three additional chromosomal substitution segments from its donor parent, IR65598-112-2. All three segments significantly enhance the expression of FZP and reduce the occurrence of tertiary branch and spikelet degeneration. These findings enhance our understanding of the mechanisms regulating FZP and aid rice breeding efforts.