Wounding response in young Scots pine stems

We studied the stress response of five-year-old Scots pine xylem to the mechanical wounding of xylem using RNA sequencing. In general, we observed a bimodal response in pine xylem after wounding. Transcripts associated with water deficit stress, defence, and cell wall modification were induced at the earliest time point of three hours; at the same time, growth-related processes were down-regulated. A second temporal wave was triggered either at the middle and/or the late time points (one and four days). Secondary metabolism, such as stilbene and lignan biosynthesis started one day after wounding. Scots pine synthesises the stilbenes pinosylvin and its monomethyl ether both as constitutive and induced defence compounds. Stilbene biosynthesis is induced by wounding, pathogens and UV stress, but is also developmentally regulated when heartwood is formed. Comparison of wounding responses to heartwood formation shows that many induced processes (in addition to stilbene biosynthesis) are similar and relate to defence or desiccation stress, but often specific transcripts are up-regulated in the developmental and wounding induced contexts. Interestingly, pine resin biosynthesis was not induced in response to wounding, at least not immediately.

本研究采用RNA测序（RNA sequencing）技术，探究了5年生欧洲赤松（Scots pine）木质部（xylem）遭受机械损伤后的胁迫响应。总体而言，我们观测到赤松木质部在损伤后呈现双峰型响应模式：与水分亏缺胁迫、防御反应及细胞壁修饰相关的转录本（transcripts）在损伤后最早的3小时时间点即被诱导表达，与此同时，与生长相关的生理过程则被下调；第二波时序响应则在中期和/或晚期时间点（即损伤后1天和4天）被激活。次生代谢（secondary metabolism）过程——如芪类化合物（stilbene）与木脂素（lignan）的生物合成——在损伤后1天即启动。欧洲赤松能够合成芪类化合物松素（pinosylvin）及其单甲醚，二者均为组成型与诱导型防御化合物。芪类生物合成可被机械损伤、病原菌侵染及紫外胁迫诱导，同时在心材（heartwood）形成过程中也受发育调控。对比损伤响应与心材形成过程可知，除芪类生物合成外，诸多被诱导的生理过程均与防御或脱水胁迫相关且高度相似，但在发育调控与损伤诱导两种情境下，通常会有特定的转录本被上调表达。值得注意的是，松脂生物合成并未在损伤响应中被诱导，至少不会立即被诱导。