Variation in DNA methylation and response to short-term herbivory in Thlaspi arvense

Plant metabolic pathways and gene networks involved in the response to herbivory are well-established, but the impact of epigenetic factors as modulators of those responses is less understood. Here, we studied the role of DNA cytosine methylation on phenotypic responses after short-term herbivory in <em>Thlaspi arvense</em> plants with two contrasting flowering phenotypes. We investigated the effect of experimental demethylation and herbivory treatments following a 2x3 factorial design. First, half the seeds were submerged in a water solution of the demethylating agent 5-azacytidine and the other half only in water, as controls. Then, we assigned control and demethylated plants to three herbivory categories (i) insect herbivory, (ii) artificial herbivory, and (iii) undamaged plants. The effects of the demethylation and herbivory treatments were assessed by quantifying genome-wide global DNA cytosine methylation, concentration of leaf glucosinolates, final stem biomass, fruit and seed production, and seed size. For most of the plant traits analysed, individuals from the two plant-types responded differently. In late-flowering plants, global DNA methylation did not differ between control and demethylated plants but it was significantly reduced by herbivory. Conversely, in early-flowering plants, demethylation at seed stage was still evident in leaf genomes of reproductive individuals whereas herbivory did not affect their global DNA methylation.参与植食作用应答的植物代谢通路与基因网络已得到充分阐明，但表观遗传因子作为这类应答调控因子的影响却仍不甚明晰。本研究以具有两种截然相反开花表型的菥蓂（Thlaspi arvense）为材料，探究了短期植食作用后DNA胞嘧啶甲基化在其表型应答中的作用。本研究采用2×3因子设计，对实验性去甲基化与植食处理的效应进行了探究。首先，将半数种子浸泡于去甲基化试剂5-氮胞嘧啶（5-azacytidine）的水溶液中，另一半仅浸泡于清水作为对照。随后，将对照与去甲基化植株分为三类植食处理组：(i) 昆虫植食组、(ii) 人工模拟植食组、(iii) 未损伤对照组。本研究通过定量全基因组总DNA胞嘧啶甲基化水平、叶片硫代葡萄糖苷（glucosinolates）含量、茎秆最终生物量、果实与种子产量以及种子大小，评估了去甲基化与植食处理的效应。在本研究分析的多数植物性状中，两种开花型植株的应答模式存在显著差异。在晚开花型植株中，对照与去甲基化植株的总DNA甲基化水平并无显著差异，但植食作用可显著降低其甲基化水平。与之相反，在早开花型植株中，种子阶段的去甲基化效应在生殖期个体的叶片基因组中仍可检测到，而植食作用并未对其总DNA甲基化水平产生影响。