Characterization of <it>Sucrose transporter </it>alleles and their association with seed yield-related traits in <it>Brassica napus </it>L

<p>Abstract</p> <p>Background</p> <p>Sucrose is the primary photosynthesis product and the principal translocating form within higher plants. <it>Sucrose transporters </it>(<it>SUC/SUT</it>) play a critical role in phloem loading and unloading. Photoassimilate transport is a major limiting factor for seed yield. Our previous research demonstrated that <it>SUT </it>co-localizes with yield-related quantitative trait loci. This paper reports the isolation of <it>BnA7.SUT1 </it>alleles and their promoters and their association with yield-related traits.</p> <p>Results</p> <p>Two novel <it>BnA7.SUT1 </it>genes were isolated from <it>B. napus </it>lines 'Eagle' and 'S-1300' and designated as <it>BnA7.SUT1.a </it>and <it>BnA7.SUT1.b</it>, respectively. The BnA7.SUT1 protein exhibited typical SUT features and showed high amino acid homology with related species. Promoters of <it>BnA7.SUT1.a </it>and <it>BnA7.SUT1.b </it>were also isolated and classified as <it>pBnA7.SUT1.a </it>and <it>pBnA7.SUT1.b</it>, respectively. Four dominant sequence-characterized amplified region markers were developed to distinguish <it>BnA7.SUT1.a </it>and <it>BnA7.SUT1.b</it>. The two genes were estimated as alleles with two segregating populations (F₂and BC₁) obtained by crossing '3715'×'3769'. <it>BnA7.SUT1 </it>was mapped to the A7 linkage group of the TN doubled haploid population. <it>In silico </it>analysis of 55 segmental <it>BnA7.SUT1 </it>alleles resulted three <it>BnA7.SUT1 </it>clusters: <it>pBnA7.SUT1.a- BnA7.SUT1.a </it>(type I), <it>pBnA7.SUT1.b- BnA7.SUT1.a </it>(type II), and <it>pBnA7.SUT1.b- BnA7.SUT1.b </it>(type III). Association analysis with a diverse panel of 55 rapeseed lines identified single nucleotide polymorphisms (SNPs) in promoter and coding domain sequences of <it>BnA7.SUT1 </it>that were significantly associated with one of three yield-related traits: number of effective first branches (EFB), siliques per plant (SP), and seed weight (n = 1000) (TSW) across all four environments examined. SNPs at other <it>BnA7.SUT1 </it>sites were also significantly associated with at least one of six yield-related traits: EFB, SP, number of seeds per silique, seed yield per plant, block yield, and TSW. Expression levels varied over various tissue/organs at the seed-filling stage, and <it>BnA7.SUT1 </it>expression positively correlated with EFB and TSW.</p> <p>Conclusions</p> <p>Sequence, mapping, association, and expression analyses collectively showed significant diversity between the two <it>BnA7.SUT1 </it>alleles, which control some of the phenotypic variation for branch number and seed weight in <it>B. napus </it>consistent with expression levels. The associations between allelic variation and yield-related traits may facilitate selection of better genotypes in breeding.</p>