Fine Mapping And Gene Expression Profile Of Boron Efficiency QTL AtBE1-2 In Arabidopsis Thaliana

Boron (B) is an essential micronutrient for higher plants, but the adaptability of plants to B deficiency varied widely between and within species. The studies on physiological and genetic mechanisms of B will benefit the understanding of B efficiency and genetic improvement of B nutrition trait in crops. Based on primary quantitative trait loci (QTL) analysis of B efficiency coefficient (BEC) in a Arabidopsis thaliana Ler×Col recombinant inbred line (RIL) population containing 97 lines, this study focused on the QTL mapping, and physiological function and gene differential expression under B deprivation aiming at the target QTL AtBE1-2, and the main results were shown as following:1. QTL Mapping for B efficiency1.1 By properly optimizing the phenotypic data and molecular markers data in the RIL population, the QTL analysis for B efficiency was conducted by using 3 different QTL mapping softwares, and then final QTLs loci of B efficiency were determined. Based on the correlation analysis, unconditional QTL mapping, conditional QTL mapping and epistatic interactions analysis among 3 traits (seed yield under low B condition-SYLB, seed yield under high B condition-SYHB and B efficiency coefficient-BEC) of RIL population, the results showed that there was a tightly genetic linkage relationship between SYLB and BEC, while SYHB was independent on SYLB and BEC.1.2 Based on the information of 4 QTLs for BEC detected in the RIL population, genotypic and BEC phenotypic selections were conducted for the each RIL line. 1938 (a B-efficient line) and 1961 (a B-inefficient line) were chosen out, which showed the genotype difference in the target region of AtBE1-2, identical genetic makeup in the region of the other three QTLs whilst their largest difference in BEC among the 97 RILs. With a F₂ segregation population derived from a cross between the two lines, a QTL controlling seed yield under low B was founded to co-locate at the region of AtBE1-2, it confirmed the authenticity of the target QTL AtBEl-2 for B efficiency.1.3 54 recombinants were screened from 1200 individuals in a F₂ population by two flanking markers (ATPASE and nga692) of target QTL AtBE1-2. And then SYLB, SYHB and BEC were investigated in 26 F_2:3 families derived from 26 out of 54 recombinants, results showed that the target QTL AtBE1-2 had significantly influence on the value of BEC. It validated the phenotypic effect of target QTL AtBE1-2.2. Physiological mechanism of QTL AtBE1-2 for B efficiencyAnalyzing the differences in B-related traits (B concentration, B accumulation) among four lines, her and Col-4 (parents of the RIL population), 1938 and 1961(parents of the F₂ population) at 3 developmental stages under 5 B levels, and compared with the differences with the corresponding QTLs possessed in each genotype, we deduced that the main function of QTL AtBEl-2 is to enhance the utilization of B in the silique when plants sufferred from B deficiency.3. Candidate genes at the region of B efficiency QTL AtBE1-2Based on gene expression profiles of 1938 and Col-4 in short-and long-term B deprivation, together with the chromosome position of differential expressed genes, 36 significantly differential expression genes were located in the target QTL AtBE1-2 region. 16 of them showing 4-fold changes between the two genotypes or in any one genotype under low B deprivatioin were considered as candidate gene of QTL AtBE1-2. It laid a fine foundation for next gene cloning and function validation.