Abstract
Grain size is one of the major traits that control rice grain yield and quality. The GS3 gene, a major QTL regulating grain length and weight, is the first one been identified. A mutation occurred in its N-terminal organ size regulating domain (OSR)results in a loss of function of the mutant allele gs3 and rice varieties carry this gs3 allele often produce longer grains. In this study, we exploited the CRISPR/Cas9 gene editing technology to introduce an edited gs3 allele, two guide RNAs(gRNA) targeted at the OSR of the GS3 gene were transformed into one of our indica maintainer lines, GM1B, for its grain yield and quality improvement. Through molecular analysis and sequencing, in T1 generation, a homologous edited-gs3 mutant line without tansgene was obtained and name as GM2B, then converted to CMS line GM1A by backcrossing to obtain another superior male sterile line GM2A for further tests. GM2B showed improved grain quality and yield compared to the WT GM1B, with grain length increased by 7.9%, length/width ratio increased from 3.89 to 4.19, TGW increased by 6.7%, and grain yield per plant increased by 14.9%. Meanwhile, genetic improvement of other quality traits including rice length (6.83mm), rice grain length/width ratio (3.61), matched the appearance standards set for traditional Simiao (silk seedling) type cultivars. Two restorer lines were outcrossed to both GM1A and GM2A to produce hybrid rice. Compared to GM1A’s two hybrids, the hybrids of GM2A had longer grains, higher length/width ratio, higher TGW and yield per plant. In addition, hybrids of GM2A showed better performance on grain appearance including better translucency, lower chalky rice rate and chalkiness degree than hybrids of GM1A.These data strongly demonstrate that the introduction of an elite gs3 allele into GM1A via CRISPR/Cas9 gene editing technology leads to significant genetic improvement. The resultant CMS line GM2A(gs3) performs much better than the original GM1A on grain quality and yield. Thus, our study proves that targeted genetic improvement using gene editing technology can expedite rice breeding, especially the breeding of three-line hybrid rice.
Population structure and association analysis of yield and grain quality traits in hybrid rice primal parental lines