Abstract
This review deals with important issues in regulation of terminal alternative oxidase (AOX) of plant mitochondria, which are currently investigated and discussed. AOX ensures electron transport along the alternative nonphosphorylating cyanide-resistant pathway in mitochondrial ETC and plays an important role in the maintenance of redox balance in the cell and defense against stress. Principal results concerning AOX signaling were obtained in the works dealing with expression of the АОХ1а gene of Arabidopsis thaliana (AtAOX1a). Reports about АОХ expression in different plant species were analyzed. Mechanisms of transcriptional and posttranscriptional control over expression of АОХ genes were described. The role of some cis-regulatory elements of AtАОХ1а promoter and related transcription factors was considered. It was shown that transduction of the signal causing expression of АОХ genes may follow anterograde and retrograde pathways. Information about mitochondrial retrograde regulation of AOX and ROS-dependent and ROS-independent signal pathways of induction of АОХ expression is given. A hypothetic sequence of signal events of light induction of АОХ1а expression in wheat leaf cell in the course of greening was worked out. Interactions between AOX signaling and hormonal signal pathways, as well as induction of АОХ by the signals of plastid origin, were described. In conclusion, it was highlighted that AOX is integrated into the common signal pathway of the cell and acts as a target and a regulator of signal events.
Highlights
Along with the main pathway, the inner membrane of plant mitochondria houses an alternative pathway (AP) via terminal oxidase called alternative oxidase (AOX)
Mitochondrial alternative oxidase is a key enzyme that directly participates in regulation of energy and redox balance of mitochondria and the whole cell
It is interesting that numerous mechanisms of transcriptional and posttranscriptional control operate in the cell; they ensure a suppression of AOX genes’ expression in normal conditions and a rapid induction of their expression under stress
Summary
Along with the main (cytochrome) pathway, the inner membrane of plant mitochondria houses an alternative pathway (AP) via terminal oxidase called alternative oxidase (AOX). AP of electron transport bypasses two points of generation of an electrochemical proton gradient (complexes III and IV) and the energy of ubiquinone oxidation by oxygen is released as heat This circumstance reduces energy efficiency of respiration but removes respiratory control that regulates the rate of ATP and NADH production depending on cell needs [1]. The majority of researchers share an opinion that, at the cellular and biochemical levels, operation of AP contributes to the maintenance of redox equilibrium in mitochondrial ETC owing to quicker oxidation of NADH and prevents generation of excess ROS This affects metabolism in mitochondria and in the whole cell.
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