Functional Characterization of Plant Ion Channels in Heterologous Expression Systems

Abstract

Plant ion channels have been confirmed as the most important membrane proteins mediating ion fluxes across the plant cell membrane, which play crucial roles in many physiological processes in living plant cells. According to the structural and functional diversity, plant ion channels can be divided into several distinct families and exhibit the great variation in ion permeability, gating property, tissue expression pattern, subcellular localization, physiological function, and regulatory mechanism. The genetic identification and functional characterization of plant ion channels have been considered as important aspects to investigate the plant physiological processes. Along with the development of molecular genetics and plant genome sequencing, more and more plant ion channel genes have been identified according to the structure alignment with animal ion channels. Although part of them have been characterized, the physiological functions of most plant ion channels are still obscure and need further studies. The electrophysiology is the special approach to investigate the ion channels, which help the researchers to understand the channel features and functions. The ionic currents mediated by plant ion channels could be recorded in the isolated protoplasts or organelles from various plant cells by using electrophysiological techniques. However, most of the plant cells simultaneously express a great number of diverse channels. It is extremely difficult to distinguish the currents which are mediated by the channel of interest. Therefore, the heterologous expression systems with few endogenous ionic conductances are employed to express and functionally characterize plant ion channel of interest. To data, a great number of heterologous expression systems have been developed for the ion channel characterization. Each system exhibits the unique features and is used for the characterization of different kinds of ion channels. The electrophysiology combining with heterologous expression systems has become the most important tool to characterize the functions of plant ion channels as well as their regulatory mechanisms. In this chapter, several commonly used heterologous expression systems are discussed, meanwhile their application in characterization of plant ion channels is also referred.