Genetic analysis and gene mapping of a rice spikelet degradation mutant (spd-hp73)

The structure of rice spikelet, an important determinant of yield and rice quality, is a hot topic in rice research areas. The structure of spikelet is somewhat complex, and its development is influenced by multiple factors, including genetic factors and environmental factors. Two major technical routes in studying molecular mechanism of the structure of spikelet are used: one is homologous sequencing of the dicotyledonous plant to screen the rice cDNA library and obtain the related genes, and the other is creating some spikelet character mutants with locating and cloning the mutant genes to grasp the genes function included.In order to further study rice spikelet development and its mechanism of regulation, we used a spikelet degradation mutant (spd-hp73), which was obtained from the offspring of hp73 mutated by ⁶⁰Co-γ radiation. In this study, the characteristic and genetic stability of rice spikelet of spd-hp73 mutant in different environments were investigated. And three crosses were made between the spikelet degradation mutant (female parent) and the wild-types Zhe7954, 9311, Minghui63 (male parents) to investigate the inheritance pattern of the mutation. And 519 SSR molecular markers were used for mutant genetic analysis. The mapping populations were derived from a cross between spd-hp73 and Zhe7954.Compared with the wild-type (hp73), the spd-hp73 mutant showed several abnormal agronomic characteristics, including weak growth, early flowering, low germination, scrubby plant, few tillers, thin stems, short leaves and clear closure of spikelet. Furthermore, the branches were twisted at different degrees, and the secondary branch was longer than hp73. Moreover, spd-hp73 exhibited abnormal inflorescence architecture, including the abundant degradation of spikelet, significant reduction of the grains per spikelet, low grain density and decreased seed setting rate. The traits of mutant were expressed stably in different growth environments. Spikelet degradation mutant resulted in a remarkable negative effect on rice normal growth and reproductive growth. Genetic analysis indicated that the special phenotype was controlled by a single recessive gene, named spd-hp73. The mutation site was preliminarily mapped to the long arm of chromosome 4 between SSR markers RM471 and RM273 with 12.2 cM and 9.4 cM intervals, respectively.These results of preliminary genetic analysis lay a foundation for fine mapping and cloning of spikelet degradation gene. Probably, spd-hp73 plays an important role in further understanding the regulation mechanism of entire spikelet development.