Pleiotropy in the wild: the dormancy gene DOG1 exerts cascading control on life-cycles

In the wild, organismal life cycles occur within seasonal cycles, so shifts in the timing of developmental transitions can alter the seasonal environment experienced subsequently. Effects of genes that control the timing of prior developmental events can therefore be magnified in the wild because they determine seasonal conditions experienced by subsequent life stages, which can influence subsequent phenotypic expression. We examined such environmentally-induced pleiotropy of developmental-timing genes in a field experiment with Arabidopsis thaliana. When studied in the field under natural seasonal variation, an A. thaliana seed-dormancy gene, Delay Of Germination 1 (DOG1), was found to influence not only germination, but also flowering time, overall life history, and fitness. Flowering time of the previous generation, in turn, imposed maternal effects that altered germination, the effects of DOG1 alleles, and the direction of natural selection on these alleles. Thus under natural conditions, germination genes act as flowering genes and potentially vice versa. These results illustrate how seasonal environmental variation can alter pleiotropic effects of developmental-timing genes, such that effects of genes that regulate prior life stages ramify to influence subsequent life stages. In this case, one gene acting at the seed stage impacted the entire life cycle.

自然生境中，生物的生命周期嵌套于季节周期之内，发育转变的时序变化会改变后续生命阶段所经历的季节环境。因此，调控前期发育事件时序的基因，其效应在自然生境中会被放大：这类基因决定了后续生命阶段所处的季节条件，而这些条件又会影响后续的表型表达（phenotypic expression）。我们以拟南芥（Arabidopsis thaliana）为实验材料，通过田间实验探究了这类环境诱导的多效性（environmentally-induced pleiotropy）。在自然季节波动的田间环境中开展研究时，我们发现拟南芥的种子休眠基因延迟萌发1（Delay Of Germination 1, DOG1）不仅调控种子萌发，还能影响开花时间、整体生活史以及适合度（fitness）。进一步分析显示，亲代的开花时间会产生母本效应（maternal effects），进而改变种子萌发过程、DOG1等位基因的遗传效应，以及这些等位基因所受自然选择（natural selection）的作用方向。由此可见，在自然条件下，萌发基因可兼具开花基因的功能，反之亦然。本研究结果阐明了季节环境波动如何重塑发育时序基因的多效性，使得调控前期生命阶段的基因效应得以蔓延扩散，进而影响后续生命阶段。在本案例中，一个仅在种子阶段发挥功能的基因，能够调控整个生物体的生命周期。