Mapping And Breeding Utilization Research Of DTH6,a Heading Date Gene In Rice

Rice plays an important role in the world's grain production,and the high and stable yield of rice is related to people's livelihood and social stability.The heading date determines the regional adaptability of rice and also affects the yield of rice,which is one of the important factors to be considered in rice breeding.Rice varieties with suitable heading date can make full use of the temperature and light resources in their planting regions,so as to obtain high yield and avoid the decline of yield and quality caused by low temperature and frost.Digging and cloning the genes related to heading date of rice is not only conductive to find out the regulation mechanism of heading date,but also of great significance to improve heading date in rice breeding.The heading date of rice is affected by multiple environmental factors such as temperature,light,soil,etc.,which is controlled by major and minor genes,and the underline genetic mechanism is very complex.To date,there have been many studies on heading date of rice,but the understanding of genetic network of regulation at heading stage is still not comprehensive.In rice breeding,especially in the subspecies breeding,the transgressive phenomenon of F1 generation often occurs and cause late maturity,which becomes one of the main obstacles to the utilization of heterosis.Therefore,it is necessary to identify the heading date genes and study their molecular functions,which would further improve the genetic network of heading date regulation and provide theoretical guidance for the precise regulation of heading stage in rice breeding.In previous studies,we constructed the introgression lines(designed as T1-T133)with Huanghuazhan as donor parent and WY3R(Wuyujing3 with the resistance to rice stripe virus)as recipient parent.Two lines,T1 and T96,were identified to have earlier heading date than that of WY3R.We constructed subsegregating populations from the crosses of WY3R and T1,WY3R and T96,respectively,for mapping the heading date genes.A new heading date gene,DTH6,was identified.These results lay a foundation for the cloning of DTH6 and further elucidating the regulation mechanism of heading date,which would contribute to the molecular improvement of heading date.The results are as follows(1)From 2017 to 2019,T1,WY3R and F1 of T1/WY3R were planted in the main season of Yangzhou and winter in Hainan,respectively.T he short day-length treatment and sowing by stages were conducted in Yangzhou.The heading dates of T1,WY3R and their F1 was 81 days,102 days and 86 days,respectively,under the long-day condition in Yangzhou normal season.The heading dates of T1 were similar under the short-day condition of winter in Hainan and short day-length treatment in Yangzhou,but the shorter heading dates of WY3R were observed.The above results showed that the photosensitivity of T1 and F1 was significantly weaker than that of WY3R.(2)By the heading dates of plants in T1/WY3R F2 population,a gene with incomplete dominance was found to control the segregation on heading date.With 8500 plants from the T1/WY3R F2 F3 and F4 populations,the target gene was mapped on chromosome 6 and located in a region adjacent to Hd1 in the direction of the short arm.These results indicated that there was a new heading date gene in T1,and the heading date gene was subsequently named as DTH6.Further,by re-sequencing the exchange indivuals,we speculated that DTH6 may derive from natural mutation.(3)In 2018,33 rice varieties with different heading dates and their F1s were planted in Yangzhou to explore the utilization value of DTH6 in breeding.The heading dates of most F1s were significantly earlier than that of their original parents,and the difference was more obvious in the F1s from late-maturing varieties with strong photosensitivity.These results indicated that DTH6 could effectively reduce the photosensitivity of varieties in most genetic backgrounds,which could be used for improving the transgressive problem in breeding of hybrid rice.(4)From 2017 to 2019,the improvement of the restorer YR6 were conducted using T1 as the donor with molecular marker assisted selection,and three improved lines(BC3F2)were obtained.The agronomic traits of the improved lines and YR6 were observed in 2019,and the improved lines exhibited the similar traits with YR6 except for the slightly decreased primary spikelet number and thousand-grain weight.