The cellular language ofmyo‐inositol signaling

Summary The simple polyol, myo‐ inositol, is used as a building block of a cellular language that plays various roles in signal transduction. This review describes the terminology used to denote myo‐ inositol‐containing molecules, with an emphasis on how phosphate and fatty acids are added to create second messengers used in signaling. Work in model systems has delineated the genes and enzymes required for synthesis and metabolism of many myo‐ inositol‐containing molecules, with genetic mutants and measurement of second messengers playing key roles in developing our understanding. There is increasing evidence that molecules such as myo‐ inositol(1,4,5)trisphosphate and phosphatidylinositol(4,5)bisphosphate are synthesized in response to various signals plants encounter. In particular, the controversial role of myo‐ inositol(1,4,5)trisphosphate is addressed, accompanied by a discussion of the multiple enzymes that act to regulate this molecule. We are also beginning to understand new connections of myo‐ inositol signaling in plants. These recent discoveries include the novel roles of inositol phosphates in binding to plant hormone receptors and that of phosphatidylinositol(3)phosphate binding to pathogen effectors. Contents Summary 823 I. Introduction 824 II. Structural and terminology considerations: adding phosphates and fatty acids to myo‐ inositol creates a chemical and cellular language for signaling 824 III. Hydrolysis of membrane PtdInsPs results in second messenger production 825 IV. What signals are linked to inositol signaling? 826 V. The controversial roles of DAG and Ins(1,4,5)P 3 in the plant cell 826 VI. A Multiplicity of enzymes that synthesize and metabolize Ins(1,4,5)P 3 829 VII. New connections of inositol signaling in plants 831 VIII. Concluding remarks 834 Acknowledgements 834 References 834