Optimization Of Rice Productivity Across A Large Latitudinal Gradient Using Induce Mutation In Heading Date

Rice(Oryza.Sativa)has a long history of domestication and main food crop in the word,which provides energy for daily use.China has extensive rice cultivation area with large latitude span(from 53°N to 35°S).Rice is a short daylength cereal which has strong regional adaptability.Heading is an important agronomic character of rice,which is determined by the genetic characteristics of rice varieties.However,short heading date will lead to dwarf plant and affect the final yield due to insufficient basic nutrition.And too long heading will affect rice grain ripening due to temperature drop,and finally reduce or even no harvest.Therefore,it is very significant to explore the optimum gene combination in rice heading time to improve the adaptability of rice region.This study is mainly divided into the following five aspects:1.CRISPR/Cas9 gene-editing technology was used to knock out the main heading date gene in the same genetic background,and the days to heading(DTH)and yield related traits of wild-type and mutants were investigated.The effect of heading date on yield related traits and the relationship between heading and yield were preliminarily analyzed.The results showed that the early mutants had a shorter photoperiod sensitive phase(PSP)but similar basic vegetative growth compared to the WT.While the late mutants had longer basic vegetative growth.In terms of yield-related traits,the plant height,biomass and yield of mutant that heading earlier than WT were generally reduced.In particular,the photosensitive gene mutants(se13、phyb、ghd7、dth8、hd1ghd7、hd1dth8、hd1ghd7dth8)significantly reduced the yield due to the greatly shortened vegetative growth period.2.The gene editing materials were planted in four regions with large latitude span(Heilongjiang,Liaoning,Jiangsu and Guangdong),and the heading period and yield of the four regions were further investigated.The results showed that the variation patterns of the DTH and yield were different between high and low latitudes.The vegetative growing phase of plants in high and mid-high latitudes was longer.In the middle and low latitudes,the DTH is very short,and the yield always increases with the changing of heading time.The photoperiodic sensitive mutant genes have obvious advantages in high latitude.3.72 japonica rice cultivars from four regions(Heilongjiang,Liaoning,Shandong,Jiangsu)were collected and High-throughput sequencing was performed.72 cultivars were also planted in four regions with large latitude spans.On the one hand,GWAS and phylogenetic tree analysis were carried out.On the other hand,genetic variation of the heading time genes in the main varieties were investigated.The results showed that the japonica varieties in Liaoning had more indica pedigree introgression than the Heilongjiang varieties.Rice was more photosensitive at high latitudes,especially at the Hd1 locus.The nonfunctional alleles(hd1 and ghd7)of the two photosensitive genes are mainly concentrated in the high latitude materials,while dth8 is mainly distributed in Jiangsu materials.The two florigen genes Hd3 a and RFT1 are relatively conserved in evolution process.Although they have different alleles,no base insertion or deletion occurs in the coding region of the gene during the whole breeding process.In addition,the gene sequence of photosensitive pigment synthesis gene Se13 is strongly conservative,with no changes in other coding and non-coding areas except for the base deletion or substitution of some materials.4.The yield-related traits of 72 japonica rice materials were analyzed in this study,and the results showed that the materials planted in the four regions would show the adaptability or inadaptability to the environment(temperature,light)among various traits in different latitude region,which was finally reflected in the yield level.The investigation found that the material yield of Heilongjiang and Liaoning regions did not increase with the changes of environmental and light conditions,and the grain number per panicle,1000-grain weight and seed setting rate of Heilongjiang materials planted in Jiangsu region significantly decreased,resulting in a significant decrease in yield.In addition,Jiangsu and Shandong materials planted at high latitudes showed great discomfort to the environment and climate change.Due to the long vegetative growth period and the arrival of frost’s descent,the plants were eventually higher but could not heading at the suitable temperature.According to the results of the investigation,there was no heading time gene combination with strong regional adaptability and optimal yield potential among the 72 japonica materials.5.According to the research,an ideal combination of flowering genes was proposed to combine weak photoperiod sensitivity with long vegetative growth period.Using CRISPR/Cas9 technology,the photosensitive related mutants which combined with ehd1 mutants generated six double-mutant lines(phybehd1,se13ehd1,dth8ehd1,ghd7ehd1,hd1ehd1,and se14ehd1)and planted in four areas along with the wild type.The results showed that the adaptability of the double mutant lines was significantly improved compared with the wild type,and it could be applied to the cultivation of japonica rice varieties with strong adaptability.In summary,this study clarified the effect of the heading time genes on the heading time and yield components,explored the heading time gene combinations with the optimal yield in different region,and polymorphism analysis and GWAS were performed on 72 japonica rice varieties.In this study we proposed new heading time mutant gene combinations with strong regional adaptability.