Brock Marcus T, Tiffin Peter, Weinig Cynthia
Department of Plant Biology, University of Minnesota, 1445 Gortner Avenue, Saint Paul, Minnesota 55108, USA.
Mol Ecol. 2007 Jul;16(14):3050-62. doi: 10.1111/j.1365-294X.2007.03298.x.
Identifying the molecular genetic basis of intraspecific variation in quantitative traits promises to provide novel insight into their evolutionary history as well as genetic mechanisms of adaptation. In an attempt to identify genes responsible for natural variation in competitive responses in Arabidopsis thaliana, we examined DNA sequence diversity at seven loci previously identified as members of the phytochrome B signalling network. For one gene, GIGANTEA (GI), we detected significant haplotype structure. To test for GI haplogroup-phenotype associations, we genotyped 161 A. thaliana accessions at GI and censused the same accessions for total fruit set and the expression of three phenotypic traits (days to flowering, petiole length, and inflorescence height) in a greenhouse experiment where plants were grown in crowded and uncrowded environments. We detected a significant association between GI and total fruit set that resulted in a 14% difference in average fruit set among GI haplogroups. Given that fruit set is an important component of fitness in this species and given the magnitude of the effect, the question arises as to how variation at this locus is maintained. Our observation of frequent and significant epistasis between GI and background single nucleotide polymorphisms (SNP), where the fitness ranking of the GI allele either reverses or does not differ depending on the allele at the interacting SNP, suggests that epistatic selection may actively maintain or at least slow the loss of variation at GI. This result is particularly noteworthy in the light of the ongoing debate regarding the genetic underpinnings of phenotypic evolution and recent observations that epistasis for phenotypic traits and components of fitness is common in A. thaliana.
确定数量性状种内变异的分子遗传基础，有望为其进化历史以及适应的遗传机制提供新的见解。为了确定拟南芥竞争反应自然变异的相关基因，我们检测了先前被鉴定为光敏色素B信号网络成员的7个位点的DNA序列多样性。对于一个基因，即巨大基因（GIGANTEA，GI），我们检测到了显著的单倍型结构。为了测试GI单倍型组与表型的关联，我们对161份拟南芥种质进行了GI基因分型，并在温室实验中对相同种质的总坐果数以及三个表型性状（开花天数、叶柄长度和花序高度）的表达进行了统计，实验中植株分别种植在拥挤和不拥挤的环境中。我们检测到GI与总坐果数之间存在显著关联，这导致GI单倍型组之间的平均坐果数相差14%。鉴于坐果数是该物种适合度的一个重要组成部分，且考虑到这种效应的大小，就产生了这样一个问题：该位点的变异是如何维持的。我们观察到GI与背景单核苷酸多态性（SNP）之间频繁且显著的上位性，其中GI等位基因的适合度排名要么反转，要么根据相互作用SNP处的等位基因而无差异，这表明上位性选择可能积极维持或至少减缓GI位点变异的丧失。鉴于目前关于表型进化的遗传基础的争论，以及最近观察到拟南芥中表型性状和适合度组成部分的上位性很常见，这一结果尤其值得注意。
