Genetic Study On Heterozygous Male Sterility Mediated By Rtms6 And Rtms10, Two Low Temperature-sensitive Genic Male Sterile Genes In Rice

Hybrid rice technology significantly improved rice yield level through utilization of heterosis.At present,the three-line method based on cytoplasmic male sterility and the two-line method based on photo-temperature sensitive nuclear sterility are the main types of hybrid rice technology.The application and popularization of these technical achievements have made great contributions to increasing rice production and ensuring food security in China.However,technical problems such as the lack of freedom for crossing in three-line method and the risk of seed production of two-line method have become an important limiting factor for the popularization and application of hybrid rice technology.Therefore,the development of a new hybrid rice technology with crossing freely and low risk of seed production is greatly significant for the safe production and sustainable development of hybrid rice.Yannong S(YnS)is a reverse thermo-sensitive genic male sterile(r TGMS)line,with low temperature male sterile and high temperature fertile.The critical temperature for fertility conversion of YnS is 29-29.5?.critical temperature for fertility conversion is29-29.5?.Breeders have bred several two-line hybrid varieties by using YnS as maternal parent.However,the genetic pattern of the low temperature sensitive sterility traits is still unclear in YnS,The mapping and cloning of sterile genes were also not reported.Moreover,previous studies have found that,the hybrid F₁ between YnS and Nongken 58S(or its derived sterile line 7001S)showed stable male sterility under various photoperiod and temperature conditions.Then,we developed a stable male sterile rice line Tianfeng HS by using the trait.Therefore,it is necessary to deeply analyze the YnS genotype and further reveal its genetic performance through mapping and cloning of related male sterile gene(s)and developing molecular markers,so as to better apply in hybrid rice breeding.In this study,we firstly performed genetic study on the trait of low temperature sensitive male sterility in YnS,then finely mapped and cloned the related sterile genes,finally revealing the genetic performance and application prospect of the stable male sterility mediated by low temperature-sensitive male sterile gene(s).The main conclusions are as follows:(1)We mapped two major loci rtms6 and rtms10,located on chromosomes 6 and 10 respectively,for controlling r TGMS in rice by using F₂ population from YnS crossed with two normal fertile lines,R608 and L422.rtms6 and rtms10 were then narrowed into?87kb and?55kb intervals by using high-generation backcrossed segregation populations,respectively.Transcriptome sequencing and RT-PCR analysis showed that the expression of Loc?Os06g08380 was specifically down-regulated in young spikelets in sterile lines under 22? condition.Genetic complementation test confirmed Loc?Os06g08380 as rtms6.The candidate gene of rtms10 was also predicted by transcriptome sequencing and RT-PCR analysis.The gene cloning and validation are in progress.(2)We developed near-isogenic lines(NILs)with carrying rtms6,rtms10,rtms6rtms10 in R608 and L422 background.Then,these NILs were crossed to 1892S.The results showed that only the NIL line(rtms6-rtms10)crossed with 1892S showed stable male sterility grown under conditions with no matter long-day and high-temperature (LD+HT)or short-day and low temperature(SD+LT),suggesting the stable male sterility resulting from the interaction of rtms6 and rtms10.(3)The low and high generation backcrossed segregation populations from YnS crossed with 1892F(recurrent male parent)were constructed.Under the LD+HT and SD+LT conditions,the segregation ratio of stable sterile plants and fertile plants was 1:1. The results of molecular marker analysis showed that the stable male sterility was co-segregated with rtms10,but not linked to rtms6,indicating that 1892F also carry the allele of rtms6.Therefore,we conclude the genotype of the stable male sterile plant as rtms6^YnSrtms6^YnSrtms10^YnSrtm10^1892F.Thus,we named the stable male sterility of F₁ between YnS and Nongken 58S(or its derived sterile lines,such as 7001S or Pei'ai 64S)as heterozygous male sterility,HMS.(4)An r TGMS line 1892RS(rtms6^YnSrtms10^YnS)in 1892F(rtms6^YnSrtms10^1892F) background was developed by molecular breeding strategy.Through field planting and artificial climate house treatment,the hybrid F₁ of 1892RS and 1892F showed male sterility under both high and low temperature conditions.The hybrid F₁ line of between 1892RS and 1892F is called 1892HS in this study,thus 1892F is the maintainer line of 1892HS,namely as 1892HB.(5)We crossed 1892HS to Wushansimiao(WSSM),Yuehesimiao(YHSM)and R9802 respectively.The main agronomic characters,yield traits and quality traits of F₁s were investigated.The results showed that the yield and quality characters of the combination made by 1892HS were not inferior to those of the combination made by1892S,which indicated that such HMS line have good application potential in hybrid rice breeding.