Abstract
We studied the stress response of five-year-old Scots pine xylem to mechanical wounding 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 at 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. Pine resin biosynthesis was not induced in response to wounding, at least not during the first four days.
Highlights
Lignans are derived from the same monolignol subunits as lignin
The high parent–offspring heritability between heartwood and wound induced stilbene biosynthesis brings up a hypothesis that there are genetic components, e.g. regulatory genes, that are shared between the wounding response and heartwood formation
The Pinus EST collection is a combined collection of expressed sequence tags from different pine species and due to high sequence similarity between the species they have been assembled into ‘tentative consensus’ (TC) sequences as if they originated from a single taxon[24]
Summary
Lignans are derived from the same monolignol subunits as lignin. They are dimers of monolignols and, unlike lignin, optically active. Lignans have been reported to play important roles in plant defence as phytoalexins[15,17]. They are developmentally regulated and in Scots pine lignans can be found in k notwood[18]. The relatively high offspring-parent heritability for PS of 0.31 suggests shared genetic control of developmentally regulated and induced biosynthesis of PS. We wanted to extract similarities and differences between the wound response and heartwood formation, both processes being characterised by stilbene biosynthesis in Scots pine. The high parent–offspring heritability between heartwood and wound induced stilbene biosynthesis brings up a hypothesis that there are genetic components, e.g. regulatory genes, that are shared between the wounding response and heartwood formation
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