Mapping And Candidate Gene Analysis Of QTL QLHD-7 For Heading Date In Rice(Oryza Sativa L.)

Rice（Oryza sativa L.）,as a staple food crop for more than half of the world’s population,has always been a hot spot in plant scientific research.Heading date is one of the important factors that determine the ecological adaptability and yield of varieties in rice.Heading date often exhibits genetic characteristics jointly determined by major genes and quantitative traits in rice,and its regulation mechanism is very complicated.Therefore,understanding and clarifying the genetic basis and molecular regulation mechanism of heading date,mining genetic resources that control heading date,cultivating rice varieties with universal adaptability and increasing yield are of great significance.In this study,the early heading indica strain YR1 was used as the donor parent,and the popularized variety NG1 was used as the recurrent parent.After crossing,backcrossing,and selfcrossing,the BC₂population separated at heading date was obtained,and the QTL controlling heading date was mapped and candidate gene was analyzed.The results of the study are as follows:1.Genetic analysis showed that the proportion of the number of early and late heading plants in BC₂F₄segregation population was 3:1.The heading date of the early-heading plants in the population was the same as that of the late-heading parent NG1,while the heading date of the late-heading plants later than NG1,indicating that there is a locus from the early heading parent YR1 delay the heading under the background of NG1.2.120 pairs of molecular markers with good polymorphism evenly distributed on 12chromosomes were selected between the parents,and then detect the source of chromosome fragments and select the linkage markers at the same time in the early heading and late heading DNA mixed pool of the BC₂F₄segregating population.It was identified that more than 90%genetic background of the BC₂F₄segregating population was homozygous;the marker M26 was heterozygous in the late heading DNA pool and homozygous for NG1 in the early heading DNA pool,that is,M26 was a linkage marker;Markers were added to the flanks of M26,and a major QTL for heading date was located in the 653 kb physical interval between the markers M26～RM22188 at the end of chromosome 7.The LOD values in the two BC₂F₄populations tested were 77.76 and 65.79,respectively,79.02%and32.04%variation of heading date were explained,respectively.The effect of delayed heading date comes from the early maturity parent YR1,and the locus was named qLHD-7.3.The Residual Heterozygous Line of qLHD-7 developed into a BC₂F₅segregating population to confirm the genetic stability of qLHD-7 and fine-mapping of qLHD-7.The results showed that qLHD-7 could still be detected at the end of chromosome 7,and it was further narrowed down to the 623.5kb interval between the markers RM22152～RM22188,the LOD value was 66.06,which explained 71.53%variation of the heading date.Markers were added to the initial location interval of qLHD-7,and 2154 BC₂F₅individual plants were used to select exchange individual plant,and qLHD-7 was limited to the 131.9kb interval between the markers RM22174～RM22188.This interval is annotated with 21 Open Reading Frames（ORFs）,which contains a rice photoperiod sensitive gene DTH7（Os PRR37/Ghd7.1）,which can significantly delay the heading date under long-day condition.The DTH7 coding region sequence has 10 Single Nucleotide Polymorphisms（SNPs）in YR1 and NG1,caused 9 amino acid differences.Compared with the reported DTH7,there are also SNP4 and SNP9 variants in the conserved region.Therefore,it is considered that there are functional differences between the allelic DTH7^YR1and DTH7^NG1.4.Compared with the high temperature and long day（Nanjing summer）environment,YR1 delays the heading date in the low temperature and short day（Hainan winter）environment,wihch lacks short-day sensitivity and shows temperature sensitivity;NG1 has earlier heading date,shows photoperiod sensitivity;Under long-day condition in Nanjing,the Near Isogenic Lines qLHD-7Y has a later heading date than qLHD-7N,DTH7^YR1delays heading under long-day condition and functions in NG1.Under long-day condition,the analysis of the expression of key genes in the flowering pathway of photoperiod regulation at the initial stage of panicle differentiation shows that the expression levels of Hd1 in the parents and qLHD-7Y lines were not significantly different,while the expression levels of Ehd1,Hd3a and RFT1 were down-regulated in NG1 and the down-regulation was more prominent in the qLHD-7Y lines,indicating that qLHD-7 inhibited the expression of Hd3a and RFT1 through the Ehd1 pathway under long-day condition,and delays heading.