The Arabidopsis DNA methylome is relatively impervious to abiotic stress

Improving plant stress response holds great agricultural potential. One promising, yet speculative, possibility is the formation of plant stress memory facilitating enhanced responses to recurring stress. One possibility is the involvement of environmentally-induced variation in reversible chromatin marks, such as DNA methylation, leading to the altered regulation of underlying genetic elements that promote enhanced stress tolerance. Such potential has spurred numerous investigations yielding conflicting results, thus it remains unclear whether robust stress-induced chromatin variation can encode plant stress memory conveying enhanced stress tolerance. Herein we investigate for the possibility of stress-induced alterations in DNA methylation to convey stress memory, both on mitotic and transgenerational timescales, such that previously stressed plants show improved stress tolerance with correlated alterations in DNA methylation at stress-responsive loci. We find that although the experience of stress may be stored mitotically, it does not appear to be transmitted meiotically and is independent of DNA methylation changes. Overall, the DNA methylome appears to be robust against stress-induced variation and is unlikely to contribute to any form of stress memory. Whole genome bisulfite sequencing was performed on plants exposed to a nine day drought stress ('mitotic drought', 3 biological replicates), repeated excess light stress over 1 week (1xWLRS, 3 biological replicates) and on progeny of 5th generation plants ('G5', 6 biological replicates per treatment) from independent lineages that were propagated by single seed descent under control conditions ('Watered') or with a recurring drought stress ('Drought') every generation.

提升植物胁迫响应能力具有重要的农业应用价值。其中一项颇具前景但仍属推测性的可能方向是，植物胁迫记忆（stress memory）的形成可助力植物增强对反复遭遇胁迫的响应能力。有假说认为，环境诱导的可逆染色质修饰（reversible chromatin marks）变异——例如DNA甲基化（DNA methylation）——可改变下游调控元件的表达，进而提升植物胁迫耐受性。该潜在应用价值已引发大量相关研究，但所得结论彼此矛盾，因此目前仍无法明确：稳定的胁迫诱导染色质变异是否能够编码植物胁迫记忆，从而赋予植物更强的胁迫耐受性。本研究旨在探究胁迫诱导的DNA甲基化变异传递胁迫记忆的可能性，分别考察有丝分裂周期与跨代两个时间尺度，即：经胁迫预处理的植物可表现出更强的胁迫耐受性，且其胁迫响应位点的DNA甲基化会出现相应变异。研究结果显示，尽管胁迫经历可在有丝分裂过程中留存，但似乎无法通过减数分裂传递，且该过程与DNA甲基化变化无关。总体而言，DNA甲基化组（DNA methylome）对胁迫诱导的变异具有较强抗性，不太可能参与任何形式的胁迫记忆形成。本研究对以下三类样本开展了全基因组亚硫酸氢盐测序（whole genome bisulfite sequencing）：① 经9天干旱胁迫处理的植株（「有丝分裂干旱组」，3个生物学重复（biological replicates））；② 连续1周经受反复强光胁迫的植株（「1xWLRS」，3个生物学重复）；③ 来自独立谱系的第5代植株子代：这些谱系均通过单粒传代（single seed descent）繁育，分别在正常培养条件（「浇水组」）或每代均施加反复干旱胁迫（「干旱组」），每组设置6个生物学重复。