Abstract
BackgroundGrain size, which is determined by grain length, grain width, and grain thickness, is an important determinant for grain yield in rice. Identification and characterization of new genes that are associated with grain size will be helpful for the improvement of grain yield in rice.ResultsWe characterized the grain size mutant, larger grain size 1 (lgs1), derived from rice activation-tagged T-DNA insertion lines. Histological analysis showed that increased cell numbers in the longitudinal direction of spikelet hulls was responsible for the grain mutant phenotype in lgs1. Quantitative real-time PCR (qRT-PCR) analysis further showed that the expression levels of genes associated with the cell cycle in the young panicles of the lgs1 were higher than those in the wild type (WT), which might result in the increased cell numbers in lgs1 spikelet hulls. Insertion site analysis together with transgenic experiments confirmed that the lgs1 phenotype was caused by enhanced expression of truncated OsbHLH107, corresponding to the nucleotide (nt) 331–846 region (i.e., the transcriptional activation region of OsbHLH107) of the OsbHLH107 coding sequence (CDS). OsbHLH107 is a nucleus-localized bHLH transcription factor, which can form a homodimer with itself. Phylogenetic analysis showed that OsbHLH107 belonged to the same subfamily as OsPILs. OsPIL13 (OsPIL1) and OsPIL16 (APG) were reported to regulate grain size in rice. By transgenic experiments, we found that OsPIL11 could also regulate grain size.ConclusionWe concluded that OsbHLH107 and its homologs are important regulators of grain size development and might be useful for grain yield improvement in rice.
Highlights
Grain size, which is determined by grain length, grain width, and grain thickness, is an important determinant for grain yield in rice
We found that OsPIL11, a homolog of OsbHLH107, regulates grain size
Statistical analysis showed no significant differences in plant height, heading date, tiller number per plant, primary branch number per panicle, spikelet number per panicle, and fully filled grain number per panicle between wild type (WT) and lgs1 (Additional file 1: Figure S1d-i)
Summary
Grain size, which is determined by grain length, grain width, and grain thickness, is an important determinant for grain yield in rice. Genetic and environmental factors determine grain yield. Genetic factors determine potential grain yield, and environmental factors determine how much of that potential can be captured. Grain yield in rice is determined by grain number per panicle, panicle number per plant, and grain weight (Zhou et al, 2017). When grain number per panicle and panicle number per plant reach optimum levels, improvement in grain weight becomes important to further increase grain yield in breeding programs (Jiao et al, 2010; Miura et al, 2010). Grain weight is determined by grain size, which comprises grain length, width, and thickness, which in turn involve cell number and size (Fukada and Kubo, 2015; Jia et al, 2016). GW2 encodes a RING-type E3 ubiquitin ligase and negatively regulates
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