Map-based cloning and transcriptome analysis of the more-tiller and small-grain mutant in rice.

MAIN
CONCLUSION: A G to T nucleotide substitution of OsTSG2 led to more tillers and smaller grains in rice by participating in phytohormone signal transduction and starch and sucrose metabolism. Rice is one of the most important food crops worldwide. Grain size and tiller number are the most important factors determining rice yield. The more-tiller and small-grain 2 (tsg2) mutant in rice, developed by ethyl methanesulfonate (EMS) mutagenesis, has smaller grains, more tillers, and a higher yield per plant relative to the wild-type (WT). Based on the genetic analysis, the tsg2 traits were conferred by a single recessive nuclear gene located on the long arm of chromosome 2. After fine-mapping the OsTSG2 locus, a G to T nucleotide substitution was identified, which resulted in an A to S mutation in a highly conserved domain of the growth-regulation factor protein. The single-strand conformation polymorphism (SSCP) marker was developed based on the SNP associated with the phenotypic segregation of traits. The functional complementation of OsTSG2 from the tsg2 mutant to the WT led to an increase in grain size and weight. The differentially expressed genes (DEGs) identified by RNA sequencing were involved in phytohormone signal transduction and starch and sucrose metabolism. Enzyme-linked immunosorbent assay (ELISA) analysis detected variation in the indole acetic acid (IAA) and jasmonic acid (JA) content in the tsg2 inflorescence, while the cellular organization, degree of chalkiness, gel consistency, amylose content, and alkaline spreading value were affected in the tsg2 grains. The findings elucidated the regulatory mechanisms of the tsg2 traits. This mutant could be used in marker-assisted breeding for high-yield and good-quality rice.