Department of Plant Sciences, Faculty of Biosciences, Norwegian University of Life Sciences, 1432 Ås, Norway.
Department of Animal and Aquacultural Sciences, Faculty of Biosciences, Norwegian University of Life Sciences, 1432 Ås, Norway.
J Exp Bot. 2022 Jun 24;73(12):4079-4093. doi: 10.1093/jxb/erac149.
The external cues that trigger timely flowering vary greatly across tropical and temperate plant taxa, the latter relying on predictable seasonal fluctuations in temperature and photoperiod. In the grass family (Poaceae) for example, species of the subfamily Pooideae have become specialists of the northern temperate hemisphere, generating the hypothesis that their progenitor evolved a flowering response to long days from a short-day or day-neutral ancestor. Sampling across the Pooideae, we found support for this hypothesis, and identified several secondary shifts to day-neutral flowering and one to short-day flowering in a tropical highland clade. To explain the proximate mechanisms for the secondary transition back to short-day-regulated flowering, we investigated the expression of CCT domain genes, some of which are known to repress flowering in cereal grasses under specific photoperiods. We found a shift in CONSTANS 1 and CONSTANS 9 expression that coincides with the derived short-day photoperiodism of our exemplar species Nassella pubiflora. This sets up the testable hypothesis that trans- or cis-regulatory elements of these CCT domain genes were the targets of selection for major niche shifts in Pooideae grasses.
触发适时开花的外部线索在热带和温带植物类群中差异很大，后者依赖于温度和光周期可预测的季节性波动。例如，在禾本科（Poaceae）中，Pooid 亚科的物种已成为北温带的专家，这一假说认为它们的祖先从短日或中性日祖先进化出了对长日的开花反应。在 Pooid 亚科中进行采样，我们支持了这一假说，并在热带高地类群中发现了几个向中性日开花和一个向短日开花的次要转变。为了解释向短日调节开花的次要转变的近似机制，我们研究了 CCT 结构域基因的表达，其中一些基因已知在特定光周期下抑制谷类作物的开花。我们发现 CONSTANS 1 和 CONSTANS 9 的表达发生了转变，这与我们的典型物种 Nassella pubiflora 的衍生短日光周期制相吻合。这提出了一个可测试的假设，即这些 CCT 结构域基因的顺式或反式调控元件是 Pooid 禾本科植物主要生态位转变的选择目标。
