Department of Stress and Developmental Biology, Leibniz Institute of Plant Biochemistry (IPB), Halle (Saale), Germany.
Department of Bioorganic Chemistry, IPB, Halle (Saale), Germany.
Sci Rep. 2019 Mar 18;9(1):4733. doi: 10.1038/s41598-019-41276-0.
Cytosolic Ca ([Ca]) elevation is an early signaling response upon exposure to pathogen-derived molecules (so-called microbe-associated molecular patterns, MAMPs) and has been successfully used as a quantitative read-out in genetic screens to identify MAMP receptors or their associated components. Here, we isolated and identified by mass spectrometry the dipeptide γ-Glu-Leu as a component of a Phytophthora infestans mycelium extract that induces [Ca] elevation. Treatment of Arabidopsis seedlings with synthetic γ-Glu-Leu revealed stimulatory effects on defense signaling, including a weak enhancement of the expression of some MAMP-inducible genes or affecting the refractory period to a second MAMP elicitation. However, γ-Glu-Leu is not a classical MAMP since pH adjustment abolished these activities and importantly, the observed effects of γ-Glu-Leu could be recapitulated by mimicking extracellular acidification. Thus, although γ-Glu-Leu can act as a direct agonist of calcium sensing receptors in animal systems, the Ca-mobilizing activity in plants reported here is due to acidification. Low pH also shapes the Ca signature of well-studied MAMPs (e.g. flg22) or excitatory amino acids such as glutamate. Overall, this work serves as a cautionary reminder that in defense signaling studies where Ca flux measurements are concerned, it is important to monitor and consider the effects of pH.
细胞质 Ca([Ca])升高是暴露于病原体衍生分子（所谓的微生物相关分子模式，MAMPs）时的早期信号反应，并且已成功用作遗传筛选中的定量读数，以鉴定 MAMP 受体或其相关成分。在这里，我们通过质谱法分离并鉴定了二肽 γ-Glu-Leu 作为一种诱导 [Ca]升高的致病疫霉菌丝体提取物的成分。用合成的 γ-Glu-Leu 处理拟南芥幼苗显示出对防御信号的刺激作用，包括对一些 MAMP 诱导基因表达的弱增强或影响对第二 MAMP 激发的难治期。然而，γ-Glu-Leu 不是经典的 MAMP，因为 pH 调节消除了这些活性，重要的是，γ-Glu-Leu 的观察到的作用可以通过模拟细胞外酸化来再现。因此，尽管 γ-Glu-Leu 可以在动物系统中作为钙感应受体的直接激动剂起作用，但这里报道的植物中钙动员活性是由于酸化。低 pH 还塑造了研究良好的 MAMPs（例如 flg22）或兴奋性氨基酸（如谷氨酸）的 Ca 特征。总的来说，这项工作提醒人们，在涉及 Ca 通量测量的防御信号研究中，监测和考虑 pH 的影响非常重要。
