Scarcelli Nora, Cheverud James M, Schaal Barbara A, Kover Paula X
Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester, United Kingdom.
Proc Natl Acad Sci U S A. 2007 Oct 23;104(43):16986-91. doi: 10.1073/pnas.0708209104. Epub 2007 Oct 16.
Although the occurrence of epistasis and pleiotropy is widely accepted at the molecular level, its effect on the adaptive value of fitness-related genes is rarely investigated in plants. Knowledge of these features of a gene is critical to understand the molecular basis of adaptive evolution. Here we investigate the importance of pleiotropy and epistasis in determining the adaptive value of a candidate gene using the gene FRI (FRIGIDA), which is thought to be the major gene controlling flowering time variation in Arabidopsis thaliana. The effect of FRI on flowering time was analyzed in an outbred population created by randomly mating 19 natural accessions of A. thaliana. This unique population allows the estimation of FRI effects independent of any linkage association with other loci due to demographic processes or to coadapted genes. It also allows for the estimation of pleiotropic effects of FRI on fitness and inflorescence architecture. We found that FRI explains less variation in flowering time than previously observed among natural accessions, and interacts epistatically with the FLC locus. Although early flowering plants produce more fruits under spring conditions, and nonfunctional alleles of FRI were associated with early flowering, variation at FRI was not associated with fitness. We show that nonfunctional FRI alleles have negative pleiotropic effects on fitness by reducing the numbers of nodes and branches on the inflorescence. We propose that these antagonistic pleiotropic effects reduce the adaptive value of FRI, and helps explain the maintenance of alternative life history strategies across natural populations of A. thaliana.
尽管上位性和多效性的发生在分子水平上已被广泛接受，但在植物中，其对与适应性相关基因的适应值的影响却很少被研究。了解基因的这些特征对于理解适应性进化的分子基础至关重要。在这里，我们利用FRI（FRIGIDA）基因研究上位性和多效性在确定候选基因适应值中的重要性，FRI基因被认为是控制拟南芥开花时间变异的主要基因。在由19个拟南芥自然居群随机交配产生的远交群体中分析了FRI对开花时间的影响。这个独特的群体使得我们能够独立于由于种群统计学过程或共适应基因而与其他位点的任何连锁关联来估计FRI的效应。它还允许估计FRI对适应性和花序结构的多效性效应。我们发现，FRI对开花时间的解释变异比之前在自然居群中观察到的要少，并且与FLC位点存在上位性相互作用。尽管早花植物在春季条件下结出更多果实，且FRI的无功能等位基因与早花相关，但FRI的变异与适应性无关。我们表明，无功能的FRI等位基因通过减少花序上的节数和分枝数对适应性产生负面多效性效应。我们提出，这些拮抗性多效性效应降低了FRI的适应值，并有助于解释拟南芥自然种群中不同生活史策略的维持。
