Plant Aquaporins and CO2

Abstract

Aquaporins are channel proteins that facilitate the diffusion of water and small uncharged solutes across cellular membranes. Plant aquaporins form a large family of highly divergent proteins that are involved in many different physiological processes. This book will summarize the recent advances regarding plant aquaporins, their phylogeny, structure, substrate specificity, mechanisms of regulation and roles in various important physiological processes related to the control of water flow and small solute distribution at the cell, tissue and plant level in an ever-changing environment. Preface; Contents; Structural Basis of the Permeation Function of Plant Aquaporins; 1 Summary; 2 Aquaporins in Living Systems Including Plants; 2.1 Aquaporins Occur in All Kingdoms of Life; 2.2 Plant Aquaporin Sequences and Their Genome-Wide Identification; 2.3 Classification of Aquaporins; 3 Three-Dimensional Structures of Aquaporins; 3.1 Structural Information on Aquaporins Is Available from All Kingdoms of Life; 3.2 An Overall Architecture of Protomers; 3.3 A Circular Bundle and a Solute-Conducting Pore; 3.4 Cytoplasmic and Periplasmic Conical Vestibules. 3.5 Aquaporins Exist as Functional Tetramers4 A Structural Basis of Transport by Aquaporins; 4.1 Approaches to Measure Solute Transport Selectivity and Kinetic Parameters; 4.2 Solute Selectivity of Aquaporins; 4.3 Rates of Solute Transport and Mechanisms; 4.4 Dimensional Filtering and the Roles of Constrictions in Permeation of Solutes of Various Volumes; 4.5 Chemical Filtering of Solutes, Barriers for Ion or Proton Conductance Through the Pores of Monomers and Significance of NPA Signatures; 4.6 Ion Conductance Through a Central Pore of Tetramers. 4.7 Mutational Studies to Alter Transport Selectivity and Rates5 Gating Mechanisms of Aquaporins Induced by pH, Cation Binding and Phosphorylation or Lengths of Loops and Mutational Studies; 6 The Structural Knowledge of Aquaporins Has Strategic Significance in Agricultural Biotechnology, Nano-Ưbiotechnology and Environmental Sciences; References; Heteromerization of Plant Aquaporins; 1 Aquaporin Hetero-oligomerization; 2 Plant Plasma Membrane Intrinsic Proteins (PIP): The Paradigmatic Case for Hetero-oligomerization of Aquaporins. 3 Structure-Function Relationships in PIP Hetero-oligomerization3.1 Loop A; 3.2 Loop E; 3.3 Transmembrane Domains; 4 Co-expression of PIP: A Condition for Oligomerization; 5 Biological Relevance of PIP Hetero-oligomerization; 5.1 Trafficking; 5.2 Biological Activity and Substrate Specificity; 5.3 Proton-Sensing Regulation; 6 Concluding Remarks; References; Plant Aquaporin Trafficking; 1 Introduction; 1.1 PM Trafficking of PIPs; 1.1.1 ER-to-Golgi Trafficking of PIPs Dependent on Trafficking Signals and Heteromerization; 1.1.2 ER-to-Golgi Trafficking of Arabidopsis PIP2. 1 Dependent on Phosphorylation1.1.3 Downregulation of Arabidopsis PIP2s in Early Secretary Pathway; 1.1.4 PM Trafficking of PIPs Dependent on SNAREs and a Rab GTPase; 1.2 Dynamic Properties of PIPs; 1.2.1 Approaches Developed to Study the Lateral Diffusion of PIPs; 1.2.2 Approaches Developed to Study the Constitutive Cycling; 1.2.3 Stress-Induced Change of PIP Dynamics and Localization; 1.3 Polar Localization of Aquaporins in Plant Cells; 1.3.1 Polar Localization of Mammalian Aquaporins; 1.3.2 Polar Localization of Plant Aquaporins; 1.4 Trafficking of TIPs.