Natural Variation of BRD2 Allele Plays an Important Role in the Plant Height and Grain Size

Plant height and grain size are important agronomic traits that directly determine grain yield in rice (Oryza sativa L.). A number of key genes controlling plant height and grain size have been cloned and characterized in recent years. In this study, we identified the zqdm1 gene from a mutant with reduced plant height and grain size. The zqdm1 gene was revealed to be a new allele of BRASSINOSTEROID DEFICIENT DWARF 2 (BRD2), encoding a FAD-linked oxidoreductase protein involved in brassinosteroid (BR) biosynthesis pathway, and regulates plant height and grain size. A 369-bp DNA fragment was found inserted at the first exon, resulting in protein coding terminated. This mutation has not been discovered in previous studies. Complementary tests have confirmed that 369-bp insertion in BRD2 was responsible for the plant height and grain size changing in the zqdm1 mutant. Over-expression of BRD2 driven by different promoters into indica rice variety Jiafuzhan (JFZ) result in slender grains, suggested its function on regulating grain shape. In summary, the current study has identified a new BRD2 allele, which both facilitated the further study of the molecular mechanism of rice growth and development and explored new dwarf genetic resources for rice breeding.