AUTHOR=Kim Sun Ha , Shim Kyu-Chan , Lee Hyun-Sook , Jeon Yun-A , Adeva Cheryl , Luong Ngoc Ha , Ahn Sang-Nag 

TITLE=Brassinosteroid biosynthesis gene OsD2 is associated with low-temperature germinability in rice

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.985559

DOI=10.3389/fpls.2022.985559

ISSN=1664-462X

ABSTRACT=<p>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 <italic>qLTG1</italic> is associated with LTG. <italic>qLTG1</italic> 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 <italic>qLTG1</italic> is allelic to <italic>DWARF2</italic> (<italic>OsD2</italic>), which encodes cytochrome P450 D2 (LOC_Os01g10040) involved in brassinosteroid (BR) biosynthesis. Sequence comparison of the two parental lines, Hwaseong and <italic>Oryza rufipogon</italic> (IRGC 105491), revealed five single nucleotide polymorphisms (SNPs) in the coding region. Three of these SNPs led to missense mutations in <italic>OsD2</italic>, whereas the other two SNPs were synonymous. We evaluated two T-DNA insertion mutants, <italic>viz.</italic>, overexpression (<italic>OsD2</italic>-OE) and knockdown (<italic>OsD2</italic>-KD) mutants of <italic>OsD2</italic>, with the Dongjin genetic background. <italic>OsD2</italic>-KD plants showed a decrease in LTG and grain size. In contrast, <italic>OsD2</italic>-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 <italic>OsD2</italic> is associated with the regulation of LTG and improving grain size. Thus, <italic>OsD2</italic> may be a suitable target for rice breeding programs to improve rice yield and LTG.</p>