Abstract
Panicle architecture and grain size are two important agronomic traits which determine grain yield directly in rice. In the present study, a mutant named ltbsg1 (longer top branch and shorter grain 1) was isolated from the cultivar “Zhenong 34” (Oryza sativa L. ssp. indica) by ethyl methane sulfonate (EMS) mutagenesis. The target gene was studied through phenotype observation, genetic analysis, map-based cloning and functional analysis. The histocytological analysis indicated that the elongated top branch and shorter grain of mutant ltbsg1 were caused from the defects of cell elongation. The ltbsg1 gene in mutant revealed a single nucleotide substitution (G-A) in the exon 2 of LOC_Os10g25780, causing an amino acid variation (Glycine-Arginine) in the FAD (Flavin-adenine dinucleotide)-binding domain of delta (24)-sterol reductase, which was involved in the brassinosteroid (BR) biosynthesis. LTBSG1 was constitutively expressed and the protein was widely localized in chloroplast, nucleus and cytomembrane. The ltbsg1 seedlings had a lower endogenous BR level and could be restored to the phenotype of wild type by exogenous BR. The LTBSG1 knock-out lines showed similar phenotype defects as mutant ltbsg1, which confirmed that LTBSG1 was responsible for top branch elongation and grain size reduction. Furthermore, LTBSG1 along with other BR-related genes were feedback-regulated due to their obvious altered expression in mutant ltbsg1. This study demonstrated that LTBSG1 could play a new role in regulating panicle and grain development by BR biosynthetic pathway.
Highlights
Rice (Oryza sativa L.) is one of the most important cereal crops, which feeds over half of the world’s population
The panicle number per plant is largely influenced by the tillering ability; the grain number per panicle is closely related to the panicle length, the branch number, the branch length, the grain density and fertility; while the grain weight is mainly dependent on the size of grain referring to a combination of the grain length, the grain width and the thickness [2,3]
LTBSG1 was a new allele of BRD2 which encoded a delta (24)-sterol reductase and could catalyze the conversion of 24-methylenecholesterol (24-MC) to campesterol (CR)
Summary
Rice (Oryza sativa L.) is one of the most important cereal crops, which feeds over half of the world’s population. The panicle number per plant is largely influenced by the tillering ability; the grain number per panicle is closely related to the panicle length, the branch number, the branch length, the grain density and fertility; while the grain weight is mainly dependent on the size of grain referring to a combination of the grain length, the grain width and the thickness [2,3]. Both panicle architecture and grain size are important agronomic traits directly affecting the grain yield, which have been the ongoing major purposes of crop
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