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Functional Cooperativity of Enzymes of Phosphoinositide Conversion According to Synergistic Effects on Pectin Secretion in Tobacco Pollen Tubes

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Molecular Plant 2010年第5期3卷 870-881页

作者： Till Ischebeck Linh Hai Vu Xu Jin Irene Stenzel Christian Lofke ingo heilmann Department of Plant Biochemistry Albrecht-von-Haller-lnstitute for Plant Sciences Georg-August-University Gottingen Justus-von-Liebig-Weg 11 37077 Guttingen Germany Present address: Center for Biochemistry Cologne University Joseph-Stelzmann-Straβe 52 50931 Cologne Germany Present address: Department of Forest Botany Georg-August-University Gottingen Busgenweg 2 37077 Gottingen Germany Present address: Department of Plant Cell Biology Albrecht-von-Haller-lnstitute for Plant Sciences Georg-August-University Gottingen Untere Karspule 2 37073 Gottingen Germany

The Arabidopsis phosphoinositide kinases PI4Kβ1 and PIP5K5 have been implicated in the control of directional vesicle trafficking underlying polar tip growth in pollen tubes. PI4Kβ1 and PIP5K5 catalyze key consecutive steps of phosphoinositide conversion, and it appears obvious that phosphatidylinositol-4-phosphate formed by PI4Kβ1 might act as a substrate for phosphatidylinositol-4,5-bisphosphate formation by PIP5K5. However, this hypothesis has not been experimentally addressed and distinct localization patterns of PI4Kβ1, PIP5K5, and also PI-synthases （PIS） generating phosphatidylinositol suggest additional complexity. Here, the synergistic functionality of enzymes of phosphoinositide conversion was assessed. In tobacco and Arabidopsis pollen tubes, phosphoinositides influence the apical secretion of pectin, and increased pectin deposition results in characteristic morphological alterations. Catalytically active and dominant negative variants of PI4Kβ1 and PIP5K5 were systematically co-expressed in tobacco pollen tubes and the incidence of morphologies related to enhanced pectin secretion was evaluated. The data support a proposed functional interplay of PI4Kβ1 and PIP5K5 at the trans-Golgi network, mediating directional vesicle trafficking. Co-expression experiments additionally including PIS isoforms, PIS1 or PIS2, indicate that pectin secretion is synergistically mediated by PI4Kβ1 and PIPSK5 acting on Ptdlns formed by PIS2 rather than PIS1. Possible ramifications for the preferential channeling of phosphoinositide intermediates between particular isoforms of PI pathway enzymes are discussed.

关键词： Phosphatidylinositol synthase phosphatidylinositol 4-kinase phosphatidylinositol-4-phosphate 5-kinase cooperativity pectin secretion pollen tubes.

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Phosphoinositide and Inositolpolyphosphate Signalling in Defense Responses of Arabidopsis thaliana Challenged by Mechanical Wounding

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Molecular Plant 2008年第2期1卷 249-261页

作者： Alina Mosblech Sabine Konig Irene Stenzel Peter Grzeganek Ivo Feussner ingo heilmann Department of Plant Biochemistry Albrecht-yon-Hailer-Institute for Plant Sciences Georg-August-University G6ttingen Justus-von-Liebig-Weg 1137077 G6ttingen Germany

Various biochemical signals are implicated in Arabidopsis wound signalling, including jasmonic acid （JA）, salicylic acid, auxin, and Ca^2＋. 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. Concom- itantly, 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 wildtype 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.

关键词： Phosphoinositide and Inositolpolyphosphate Signalling Arabidopsis Mechanical Wounding

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