Gene Mapping And Candidate Gene Prediction Of Stem Pubescence Prostration In Soybean

Trichomes are found almost in every terrestrial plant. Different trichomes, evolved under nature selection, must have certain ecological significance. Trichome can be measured in terms of the presence or absence of trichome, density, prostration, and tip point shapes （blunt or sharp）, length, curliness, and so on. Numerous researches have suggested that the different characteristics of trichomes are relevant to the resistance to biological stresses and abiotic stresses. In recent years, related researches have suggested that there is a significant correlation of soybean pubescence characteristics with the resistance to some insects. However the same pubescence may have different influences on the resistance to different pests. Previous studies almost concentrated in the pubescences of leaf and leaf stalk in soybean, rather than the stem pubescence in soybean, and detected some QTLs. The characteristics of stem pubescence in soybean are divided into four main aspects:density, prostration, length and tip point shapes （blunt or sharp）. This research studied the stem pubescence prostration in soybean and conducted secondary mapping on the basis of rough mapping by using the bulked-segregant analysis （BSA） combined the recessive-class analysis （RCA）.We used S-27, wich is derived from the chromosome segement substitution lines of the wild soybean （SojaCSSL₁）, and Nannong 1138-2 as the parents to establish mapping population, which have a significant distinction in the pubescence prostration. Respectively, the pubescence of S-27 and Nannong 1138-2 are typically erect type and prostrate type. We found a protuberance around the base of erect pubescence, and speculated that the protuberance may result in the diffrence of pubescence prostration between two parents. By using the two parents we established a F2 pouplation containing 499 plants to conduct genetic analysis of the stem pubescence prostration. The segregation ratio of F2 is fit for the theoretical value of 3:1 through the chi-square test. Randomly selected 434 dominant plants from F3 population and identified their genotypes by observing whether their offspring segregated. The segregation ratio of F3:4 is also fit for the theoretical value of 2:1. These results indicated that the difference of pubescence prostration is caused by a pair of alleles in the mapping population. We designated the genotype of erect stem pubscence as Pp, the genotype of the prostrate stem pubscece aspp （pubescence prostration）.We randomly selected 15 prostrate stem pubescence plants and 15 erect stem pubescence plants to construct two gene pools respectively. After analysis, we found the marker Sat₃45 is polymorphic between the parents and two gene pools. Then we detected this marker in all 114 recessive plants of F2 population. The results showed this marker was linked to the stem pubescence prostration. After analysis of more SSR markers around the marker Sat₃45, we found 6 more polymorphic SSR markers between two parents and gene pools. We further detected their genotypes in the recessive plants of F2 population. We analysed all these markers’genetypes by the MapMaker 3.0 and transformed the recombination frequency into centimorgans （cM）. The rough mapping region of the gene pp, controls the stem pubescence prostration, was located at the near terminus of Dla, between the SSR markers BARCSOYSSR 010289 and BARCSOYSSR 010399. We further constructed enlarged populations, which are similar to the segregated F2 population:in 2012, we sowed the seeds of the dominant plants from F2, which are heterozygous genotypes at two markers of rough mapping, to construct F3 population; in 2013, we sowed the seeds of 434 plants, randomly selected from F3, to get F34 lines. We designed 15 more polymorphic SSR markers between two parents and gene pools for secondary mapping and located the mapping region region between the SSR markers SSPb61 and SSPb117 with approximate 248.29Kb of physical distance.There are 13 predicted genes in the mapping region. After analyzing these genes’ annotations and sequencing the PCR products of 5 genes, we considered the gene Glyma01g06121 as the potential candidate gene which encodes a homologous protein of anaphase promoting complex （APC） subunit 2. Moreover, the gene Glyma01g06150, which is adjacent to the secondary mapping region, encodes a highly homologous protein of NAM （No apical meristem）. Related studies suggested the NAM plays a pivotal role in the pubescence formation. This research made a good fundamental work for the subsequent studies:cloning of the gene pp, researching the correlation of stem pubescence between the resistance to insects and the mechanism of the pubescence formation in soybean.