Using CRISPR/Cas9 Gene Editing Technology To Create Rice Heading Date Mutants

Heading date is an important factor affecting rice(Oryza sativa L)yield,which is determined by the genetic characteristics of rice varieties.It is a critical period of transition from vegetative growth to reproductive growth during rice growth and development,and is sensitive to the response of environmental changes(temperature,light).In recent decades,many genes related to heading time have been found,and their variations contribute to the expansion of rice cultivation area.However,due to different genetic backgrounds,it is hard to compare the phenotypic effects of these genes.Based on the genetic background of a wild-type japonica cultivar Sasanishiki,14 heading time mutants were obtained by using CRISPR / cas9 gene-editing and marker-assisted selection.The relationship between photoperiod sensitivity,days to heading(DTH)and yield components of mutants were investigated.The main results are as follows:(1)We found that late heading was related to the growth period,while the growth period was related to larger biomass,which may guarantee higher yield.All early spike-drawing mutants reduced yield,which was associated with a significant reduction in yield due to inadequate growth stages of basic nutrients.yield increases with DTH,but once the peak is reached,biomass increases with heading period,but yield begins to decline.(2)The effects of mutants on DTH and yield components were significantly different.The results showed that the photosensitive gene mutants seriously affected the plant height and biomass of rice,and then affected the yield because of shortening the vegetative growth period.The yield of the double mutant decreased significantly even if similar to the single mutant heading stage.In practical application,different mutation effects of different genes can be used for gene combination,which can further increase rice yield and maximize yield potential.(3)We found that a good mutant of se14 obtained the same yield as WT,but the heading time was advanced 10 days.An excellent characteristics of se14 mutants can improve the adaptability of varieties and save labor,water and cultivated land resources.Through the sequence analysis of 72 cultivars in different japonica rice cultivation areas,it was found that elite se14 mutants had not been used in japonica rice breeding.Function of se14 mutants needs to be tested in different genetic contexts to further elucidate its effect on yield.Under the same genetic background,our study proved the effect of heading time gene on reproductive transformation and yield composition.These results provide new insights and strategy into rice breeding by using heading time mutants.