The APETALA2-Like Transcription Factor SUPERNUMERARY BRACT Controls Rice Seed Shattering and Seed Size

Abstract

The elimination of seed shattering was a crucial event during crop domestication. Improving and fine-tuning the regulation of this process will further enhance grain yield by avoiding seed losses during crop production. In this work, we identified the loss-of-shattering mutant <i>suppression of shattering1</i> (<i>ssh1</i>) through a screen of mutagenized wild rice (<i>Oryza rufipogon</i>) introgression lines with naturally high shattering. Using the MutMap approach and transformation experiments, we isolated a genetic factor for seed shattering, <i>SSH1</i>, which is an allele of <i>SUPERNUMERARY BRACT</i> (<i>SNB</i>), a gene encoding a plant-specific APETALA2-like transcription factor. A C-to-A point mutation in the ninth intron of <i>SNB</i> altered the splicing of its messenger RNA, causing the reduced shattering of the <i>ssh1</i> mutant by altering the development of the abscission layer and vascular bundle at the junction between the seed and the pedicel. Our data suggest that <i>SNB</i> positively regulates the expression of two rice <i>REPLUMLESS</i> orthologs, <i>qSH1</i> and <i>SH5</i> In addition, the <i>ssh1</i> mutant had larger seeds and a higher grain weight, resulting from its increased elongation of the glume longitudinal cells. The further identification of favorable <i>SNB</i> alleles will be valuable for improving rice seed shattering and grain yield using molecular breeding strategies.