Improving grain appearance of erect-panicle japonica rice cultivars by introgression of the null gs9 allele

Abstract

The panicle architecture and grain size of rice affect not only grain yield but also grain quality, especially grain appearance. The erect-panicle (EP) trait controlled by the qpe9-1/dep1 allele has been widely used in high-yielding japonica rice breeding, but usually accompanied with moderate appearance of milled rice. The null gs9 allele shows a good potential for improving grain shape and appearance. However, GS9 and qPE9-1/DEP1 loci are tightly linked, and their interaction is unclear, which obviously restricts their utilization in modern rice breeding. In the present study, comparative analyses of protein and mRNA levels revealed that GS9 and qPE9-1 function independently. Three near-isogenic lines (NILs) carrying various allelic combinations of these two loci, NIL (gs9/qpe9-1), NIL (GS9/qPE9-1) and NIL (gs9/qPE9-1), in the EP japonica cultivar 2661 (GS9/qpe9-1) background were developed for genetic interaction analysis. GS9 and qPE9-1 had additive effects on determining grain size, and the null gs9 allele could decrease grain chalkiness and improve grain appearance without affecting plant and panicle architecture in EP japonica cultivars. Additionally, introgression lines (ILs) developed in another released EP japonica cultivar Wuyujing 27 (WYJ27) background showed the same additive effect and the feasibility of utilizing the gs9 allele to improve grain appearance quality in high-yielding EP cultivars. This study provides an effective strategy for rice breeders to improve rice grain appearance in EP japonica and related cultivars.