Fine Mapping Of Okra Leaf Gene L2 In Upland Cotton

Cotton is the most important natural fiber crop worldwide, and also important oil and protein crop. Because of its usage and economic value, cotton has become one of the most important crash crops in the world. Leaf shape of cotton is one of the most important traits, which influences yield, flowering rate and pest resistance. Cultivated cotton is divided into two leaf shapes including normal leaf and okra leaf. Compared with the normal leaf cotton, Okra leaf cotton usually has higher light-saturated and less boll rot, as well as better pesticide penetration and resistance for pink bollworm, cotton bollworm, knot winged whitefly and cotton leaf roller, which also leads to reduce the use of insecticides.Therefore, fine mapping of okra leaf gene is important to better understand the molecular mechanism of okra leaf formation.The previous study in our laboratory has mapped the Okra leaf gene (L2) on chromosome 15 with a recombinant inbred line (RIL) population from a cross between a normal leaf cultivar (Yumianl) and an okra leaf strain (T586). In the present study, okra leaf line RIL034 derived from (T586×Yumianl) RIL population and normal leaf cultivar Yumianl, and normal leaf line Jinnong 08 were chosen to produce the F2 segregating population for fine mapping Okra leaf gene (L2). The main results are as following.1. Genetic analysis of Okra leaf gene (L2)A total of 1873 individuals were investigated in (RIL034×Yumianl) F2 population, which consisted of 462 plants with the normal leaf,449 plants with the okra leaf and 964 plants with the intermediate leaf shape. Chi-square test showed that leaf shape segregation fitted Mendelian ratio (1:2:1).2. Fine mapping of okra leaf gene212 SSR primer pairs designed from genome sequence of Gossypium ramondii, a total of 66 polymorphic primer pairs were attained between T586 and Yumianl.66 polymorphic primer pairs and 3 markers mapped at L2 region were used to genotype 92 individuals randomly selected from (RIL034×Yumianl) F2 population, and linkage analysis showed that 29 markers were linked with L2 gene.28 markers were used to genotype the rest individuals from (RIL034×Yumianl) F2 population. The linkage analysis showed that L2 gene was located between SWU7749 and SWU7354 on chromosome 15, with genetic distance 19.034 cM and 0.081cM, respectively.3. Further confirming the position of okra leaf gene310 individuals from (RIL090×Jinnong08) F2 population were investigated in June of 2014, which consisted of 72 plants with the normal leaf,93 plants with the okra leaf and 137 plants with the intermediate leaf shape. These data also fitted Mendelian segregating ration (1:2:1).SSR marker mapped at L2 region from (RIL034×Yumianl) F2 population, and SSR primer pairs designed from genome sequence of Gossypium ramondii were used to screen polymorphic primer pairs between RIL034 and Jinnong08, and 32 polymorphic primer pairs were obtained.32 polymorphic primer pairs were used to genotype 92 individuals randomly selected in F2 segregating population, and linkage analysis showed that 15 loci were linked with L2 gene.15 markers were used to genotype the rest individuals from (RIL090×Jinnong08) F2 population. The linkage analysis showed that L2 gene was located between SWU2070 and SWU7354 on chromosome 15, with genetic distance 0.161 cM and 0.074cM, respectively.4. Candidate predictionThe physical distance corresponding to the genome of G. raimondii between SWU07749 and SWU07354 was 11.661kb in (RIL034×Yumianl) F2 population, and the physical distance corresponding to the genome of G raimondii between SWU02070 and SWU07354 was 16.226 kb in (RIL090×Jinnong 08) F2 population. The L2 region corresponding to the genome of G. raimondii contained only one annotated gene(Gorai.002G244000), coding homedomain transcription factor HB51/LMI1.