Phosphoinositide and Inositolpolyphosphate Signalling in Defense Responses of Arabidopsis thaliana Challenged by Mechanical Wounding
Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany
1 To whom correspondence should be addressed. Heilmann: e-mail iheilma{at}uni-goettingen.de, fax +49 551 39 5749, tel. +49 551 39 5748. Feussner: e-mail ifeussn{at}uni-goettingen.de, fax +49 551 39 5749, tel. +49 551 39 5743
Various biochemical signals are implicated in Arabidopsis wound signalling, including jasmonic acid (JA), salicylic acid, auxin, and Ca2+. Here, we report on cross-talk of phytohormones with phosphoinositide signals not previously implicated in plant wound responses. Within 30 min of mechanical wounding of Arabidopsis rosette-leaves, the levels of the lipid-derived soluble inositolpolyphosphate, inositol 1,4,5-trisphosphate (InsP3), increased four to five-fold. Concomitantly, the precursor lipids, phosphatidylinositol 4,5-bisphosphate, phosphatidylinositol 4-phosphate and phosphatidylinositol transiently depleted, followed by re-synthesis after 30–60 min of stimulation. Increased InsP3 levels with wounding coincided with JA increases over the first hours of stimulation. In dde2-2-mutant plants deficient in JA biosynthesis, no InsP3 increase was observed upon wounding, indicating that JA was required for InsP3 formation, and InsP3 levels increased in wild-type plants challenged with sorbitol, increasing endogenous JA levels. In InsP 5-ptase plants with attenuated phosphoinositide signalling, the induction of wounding-inducible genes was diminished compared with wild-type plants, suggesting a role for phosphoinositide signalling in mediating plant wound responses. The gene-expression patterns suggest that phosphoinositides contribute to both JA-dependent and JA-independent aspects of wound signalling. Weight gain of Plutella xylostella caterpillars feeding on InsP 5-ptase plants was increased compared with that of caterpillars feeding on wild-type plants. The ecophysiological relevance of phosphoinositide signals in plant defense responses to herbivory is discussed in light of recent findings of inositolpolyphosphate involvement in phytohormone-receptor function.