Abstract
BACKGROUND: Grain size is one of the major determinants of cereal crop yield. As a class of plant polyhydroxysteroids, brassinosteroids (BRs) play essential roles in the regulation of grain size and plant architecture in rice. In a previous research, we cloned qGL3/OsPPKL1 encoding a protein phosphatase with Kelch-like repeat domains, which negatively regulates BR signaling and grain length in rice. RESULTS: Here, we screened qGL3-interacting proteins (GIPs) via yeast two-hybrid assay and analyzed the phenotypes of the T-DNA insertion mutants of GIPs. Among these mutants, mutant osak3 presents shorter grain length and dwarfing phenotype. OsAK3 encodes an adenylate kinase, which regulates grain size by controlling cell expansion of rice spikelet glume. Overexpression of OsAK3 resulted in longer grain length. OsAK3 interacts with qGL3 in vivo and in vitro. Lamina inclination, coleoptile elongation and root inhibition experiments showed that the osak3 mutant was less sensitive to exogenous brassinolide (BL) treatment. The transcriptional level of OsAK3 was up-regulated under BL induction. In addition, RNA-Seq data indicate that OsAK3 is involved in a variety of biological processes that regulate BR signaling and grain development in rice. CONCLUSIONS: Our study reveals a novel BR signaling component OsAK3 in the regulation of grain length, and provides novel clues for uncovering the potential functions of OsAK3 in rice growth and development.