Department of Plant Sciences, Norwegian University of Life Sciences, 1432 Ås, Norway.
Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden.
J Exp Bot. 2024 Oct 30;75(20):6405-6422. doi: 10.1093/jxb/erae316.
Frost tolerance has evolved many times independently across flowering plants. However, conservation of several frost tolerance mechanisms among distant relatives suggests that apparently independent entries into freezing climates may have been facilitated by repeated modification of existing traits ('precursor traits'). One possible precursor trait for freezing tolerance is drought tolerance, because palaeoclimatic data suggest plants were exposed to drought before frost and several studies have demonstrated shared physiological and genetic responses to drought and frost stress. Here, we combine ecophysiological experiments and comparative analyses to test the hypothesis that drought tolerance acted as a precursor to frost tolerance in cool-season grasses (Pooideae). Contrary to our predictions, we measured the highest levels of frost tolerance in species with the lowest ancestral drought tolerance, indicating that the two stress responses evolved independently in different lineages. We further show that drought tolerance is more evolutionarily labile than frost tolerance. This could limit our ability to reconstruct the order in which drought and frost responses evolved relative to each other. Further research is needed to determine whether our results are unique to Pooideae or general for flowering plants.
抗冻性在开花植物中已经多次独立进化。然而，在亲缘关系较远的植物中，几种抗冻机制的保守性表明，进入冷冻环境的明显独立进化可能是通过对现有性状（“前体性状”）的反复修饰而促进的。一种可能的抗冻前体性状是耐旱性，因为古气候数据表明，植物在受冻之前就已经受到干旱的影响，而且几项研究已经证明了耐旱性和抗冻性胁迫具有共同的生理和遗传响应。在这里，我们结合生态生理学实验和比较分析来检验耐旱性是冷季禾本科植物（Poaceae）抗冻性前体的假说。与我们的预测相反，我们在祖先耐旱性最低的物种中测量到了最高水平的抗冻性，这表明这两种胁迫反应在不同的谱系中是独立进化的。我们进一步表明，耐旱性比抗冻性在进化上更不稳定。这可能限制了我们重建干旱和抗冻反应相对于彼此进化的顺序的能力。需要进一步的研究来确定我们的结果是否仅适用于禾本科，还是适用于所有开花植物。
