Identification and gene mapping of hry1 mutant in rice.

The number of tillers, the number of grains per panicle and the weight of grains, which are interrelated, mutually restricted and mutually compensated. In addition, they mainly determine the grain yield per plant in rice; especially panicle number and grain number per panicle have a large negative correlation, so high yield can be obtained only in the case of coordinated development of all factors. Nevertheless, many of the modes that regulate rice grain number and grain size remain unexplained and require further study, owing to the complex regulatory modes within and among the pathways. In this study, two mutants of grain number have been identified in the background of KY131 (Kongyu131, an excellent japonica rice variety in Northeast of China) by EMS mutagens, named as hry1-1 (height, reduced tiller, yield 1-1) and hry1-2. Compared with the wild type, the hry1-1 and hry1-2 mutants have excellent agronomic traits, including the plant height, yield per plant, panicle length, number of grains per spike, grain length, grain width and grain thickness, while significantly decreased the number of tillers. Genetic analysis showed that hry1-1 and hry1-2 were allelic mutants or the same mutant, and the mutation in a recessive nuclear gene caused their phenotypes. The results of MutMap analysis based on resequencing and map cloning showed that the HRY1 was located in the 576 kb physical interval between M33 and M28 markers on chromosome 1 in rice. Cytological analysis of young panicle and glume epidermis in hry1 mutants indicated that hry1 mutant have higher cell division frequency and cell size during differentiation of young panicle. In addition, the hry1 mutants have significantly higher the expression levels of cyclin-related genes CycAs, CycBs, CycDs and CDKs than wild type, suggesting that HRY1 may be involved in panicle development and yield formation by regulating cell division in rice. In summary, HRY1 gene plays an important role in the regulation of the differentiation and development of panicle, which will provide a new idea for molecular design breeding to improve high and stable yield in rice.