LTBSG1, a New Allele of BRD2, Regulates Panicle and Grain Development in Rice by Brassinosteroid Biosynthetic Pathway

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.

Transcriptome analysis reveals important candidate genes involved in grain-size formation at the stage of grain enlargement in common wheat cultivar “Bainong 4199”

“…Many grain-size/weight genes have been successfully cloned in plants including rice and Arabidopsis thaliana [ 4 – 6 ]. More recently, studies show that LTBSG1 regulates panicle and grain development in rice by brassinosteroid biosynthetic pathway [ 7 ]. OsGW2 , encoding a ring-type E3 ubiquitin ligase, affects grain width, weight and yield by regulating cell division [ 8 ].…”

Hormonal Regulation of Spikelet Development

“…OsDof12 overexpression downregulates two positive brassinosteroid signal regulators like OsBR11 and OsBZR1 for suppression of brassinosteroid action. In conformity, Qin et al (2018) found a brassinosteroid deficient mutant named ltbsg1 showing a longer top panicle branch and shorter grain size from indica rice cultivar Zhenong 34 developed by ethyl methane sulfonate mutagenesis. In the mutant rice amino acid variation (Glycine-Arginine) in the FAD (Flavin adenine dinucleotide)binding domain of delta (24)-sterol reductase precludes brassinosteroid biosynthesis by preventing the conversion of 24-methylenecholesterol (24-MC) to campesterol (CR) in the early stage.…”

Diversity of Panicle Architecture and Traits Influencing Grain Filling

“…A gif1 mutation shows slower grain filling and exhibits increased grain chalkiness on account of abnormally developed and loosely packed starch granules. The latest report on the molecular biology of grain size comes with the identification of a brassinosteroid-deficient mutant ltbsg 1 showing longer top branches in panicle and shorter grain (Qin et al 2018). In the wild LTBSG1 located on chromosome 10 is constitutively expressed and the proteins are found in the chloroplast, cell membrane and nucleus.…”