Seed shattering is a major factor limiting rice production, and breeding new rice varieties with moderate seed shattering is a key challenge faced by rice breeders worldwide. Rice is the most important cereal crop in China, plays a vital role for national food security. Seed shattering is one of the most important traits during rice domestication, and the abscission zone is the important region to control seed shattering. Compared with wild rice, cultivar has eliminated the seed shattering with partially developed abscission layer. Seed shattering not only has a direct impact on the yield, but also affects the way of its mechanical harvest. In order to breed rice varieties with moderate seed shattering in agricultural production, it is necessary to mine and utilize important seed shattering genes and introduce them into excellent rice varieties for genetic improvement, so as to breed new rice varieties suitable for mechanical harvesting with moderate seed shattering. Several seed shattering genes had been identified by map-based cloning, such as SH4/SHA1, qSH1, OsSh1/ObSH3, and their functional mechanisms had been analyzed. At the same time, new rice materials with moderate seed shattering have been successfully developed through CRISPR/Cas9 gene editing technology, gamma ray mutagenesis technology and gene introduction methods. Seed shattering has an important effect on grain yield and rice harvesting methods, in this paper, we reviewed the methods, physiologic basis, the identification of seed shattering genes and genetic mechanism of seed shattering in rice. At the same time, it is proposed that by using the important genes in excellent rice germplasm resources, could provide reference for exploring the mechanism of rice seed shattering, and breed new rice varieties suitable for mechanical harvesting with moderate seed shattering.

In a genome-wide association study, we identified a rice UDP-glycosyltransferase gene, OsUGT706D2, whose transcription was activated in response to cold and submergence stress and to exogenous abscisic acid (ABA). OsUGT706D2 positively regulated the biosynthesis of tricin-4′-O-(syringyl alcohol) ether-7-O-glucoside at both the transcriptional and metabolic levels. OsUGT706D2 mediated cold and submergence tolerance by modulating the expression of stress-responsive genes as well as the abscisic acid (ABA) signaling pathway. Gain of function of OsUGT706D2 increased cold and submergence tolerance and loss of function of OsUGT706D2 reduced cold tolerance. ABA positively regulated OsUGT706D2-mediated cold tolerance but reduced submergence tolerance. These findings suggest the potential use of OsUGT706D2 for improving abiotic stress tolerance in rice.

Panicle architecture is an agronomic determinant of crop yield and a target for cereal crop improvement. To investigate its molecular mechanisms in rice, we performed map-based cloning and characterization of OPEN PANICLE 1 (OP1), a gain-of-function allele of LIGULELESS 1 (LG1), controlling the spread-panicle phenotype. This allele results from a 48-bp deletion in the LG1 upstream region and promotes pulvinus development at the base of the primary branch. Increased OP1 expression and altered panicle phenotype in chimeric transgenic plants and upstream-region knockout mutants indicated that the deletion regulates spread-panicle architecture in the mutant spread panicle 1 (sp1). Knocking out BRASSINOSTEROID UPREGULATED1 (BU1) gene in the background of OP1 complementary plants resulted in compact panicles, suggesting OP1 may regulate inflorescence architecture via the brassinosteroid signaling pathway. We regard that manipulating the upstream regulatory region of OP1 or genes involved in BR signal pathway could be an efficient way to improve rice inflorescence architecture.