Abstract
Pre-harvest sprouting (PHS) in cereal crops, including rice ( Oryza sativa L.), causes substantial yield and end-use quality losses worldwide. These losses could be prevented through introgression of dormancy-related genes into commercial varieties. Rc gene, which, in the absence of Rd , results in rice with brown pericarp, controls seed dormancy. Through reciprocal cross analysis, we established that Rc has a completely dominant maternal effect on pericarp color, which may confer an advantage in PHS resistance to hybrid rice over inbred rice. To investigate the effect of Rc on PHS resistance and other traits, we developed two sets of NIL-derived populations targeting the Rc locus in japonica and indica rice. In japonica rice, the sprouting percentage (SP) of seeds produced by maternal plants with an Rcrc or RcRc genotype was significantly (~43%) lower than that produced by maternal plants with an rcrc genotype. Furthermore, there was no significant difference between the SP of seeds produced by maternal plants with Rcrc and RcRc genotypes; therefore, the SP of seeds produced by maternal plants with the Rcrc genotype showed no genetic segregation, indicating that Rc has a dominant maternal effect on PHS resistance. The SP of brown hybrid seed was significantly (~50%) lower than that of white hybrid seed, indicating that the effect of Rc on PHS resistance failed to be counteracted by gibberellic acid application in hybrid seed production. In indica hybrid rice, the SP of brown hybrid rice was significantly (~48%) lower than that of white hybrid rice. Thus, Rc significantly affects PHS resistance in both japonica and indica rice. Moreover, there was no difference between the RcRc , Rcrc , and rcrc genotypes in germination percentage (GP) of after-ripened seeds and no difference between brown and white hybrid seeds in seedling establishment, indicating that releasing Rc -controlled dormancy retains seed quality and does not negatively affect the next agricultural production cycle. Further investigation showed that there was no significant difference between the milled rice qualities of brown- and white-pericarp rice, including total amylose content, hot-water-insoluble amylose content, gel consistency, alkali spreading value, rapid viscosity analyzer profile properties, crude protein content, and crude fat content. DPPH• inhibition percentage, an indicator of antioxidative capacity, of Rcrc and RcRc genotypes bran was nearly double that of rcrc . Therefore, Wide application of the Rc gene would not only protect against PHS, but would also enhance the production of naturally occurring antioxidants that could make a significant contribution to human health.Description of key termsNIL-derived population: a randomly segregated population (such as F2) developed by crossing a near-isogenic lines (NILs) with its background parent.Hybrid seed production: for rice, the use of a fertile breeding line (male parent) to pollinate a male sterile line (female parent) to produce hybrid seeds (F1), which are harvested from the male sterile line and sold to farmers to produce hybrid rice (F2 seeds as food). In the hybrid seed production, gibberellic acid (GA) application is required to increase hybrid seed yield.Highlights• Compared with a NIL, a NIL-derived population can further eliminate not only the genetic background effect but also the environmental effect.• Rc gene has a significant effect on pre-harvest sprout (PHS) resistance and Rc-controlled dormancy does not negatively affect next agricultural production cycle.• Rc gene has a completely dominant maternal effect on PHS resistance, which confers an advantage to hybrid rice over inbred rice, and the effect fails to be counteracted by GA application in hybrid seed production.• Rc gene retains the same milled rice qualities of brown-pericarp rice as that of white-pericarp rice and the brown-pericarp rice possesses a higher antioxidative capacity than the white-pericarp rice.• Wide application of the Rc gene would not only protect against PHS, but would also enhance the production of naturally occurring antioxidants that could make a significant contribution to human health.
Clonal seeds in hybrid rice using CRISPR/Cas9