Brassinosteroid biosynthesis gene is associated with low-temperature germinability in rice.

In rice, low-temperature germinability (LTG) is essential for stable stand establishment using the direct seeding method in temperate and high-altitude areas. Previously, we reported that the quantitative trait locus is associated with LTG. is also associated with tolerance to several abiotic stresses, such as salt and osmotic conditions. In this study, map-based cloning and sequence analysis indicated that is allelic to (), which encodes cytochrome P450 D2 (LOC_Os01g10040) involved in brassinosteroid (BR) biosynthesis. Sequence comparison of the two parental lines, Hwaseong and (IRGC 105491), revealed five single nucleotide polymorphisms (SNPs) in the coding region. Three of these SNPs led to missense mutations in , whereas the other two SNPs were synonymous. We evaluated two T-DNA insertion mutants, , overexpression (-OE) and knockdown (-KD) mutants of , with the Dongjin genetic background. -KD plants showed a decrease in LTG and grain size. In contrast, -OE plants showed an increase in grain size and LTG. We also examined the expression levels of several BR signaling and biosynthetic genes using the T-DNA insertion mutants. Gene expression analysis and BR application experiments demonstrated that BR enhanced the seed germination rate under low-temperature conditions. These results suggest that is associated with the regulation of LTG and improving grain size. Thus, may be a suitable target for rice breeding programs to improve rice yield and LTG.