Targeting the Plant Cysteine Oxidases to Regulate Plant Stress Tolerance

Population growth and climate change mean that food security is an emerging global challenge. Crop loss due to flood, drought and other weather extremes is something that disproportionately affects the world's poor, but also has widespread international impact. There is an immediate and urgent need to develop tools and strategies to improve crop tolerance to such abiotic stress. One effective mechanism towards this goal is molecular engineering of crops to withstand prolonged abiotic stress. Group VII Ethylene Response transcription Factors (ERF-VIIs) have a key role in plant stress tolerance, in particular flooding but also salinity, high temperature, drought and oxidative stress. ERF-VIIs are readily degraded, but their stabilisation has led to improved flood tolerance in model plants and crops. Consequently, ERF-VIIs are focal points for engineering abiotic stress resistance in crops. ERF-VIIs are destabilised when their N-terminal cysteine (Nt-Cys) residues are oxidised, making them substrates for the N-end rule pathway of protein degradation. I discovered that Plant Cysteine Oxidase enzymes (PCOs) catalyse this oxidation, incorporating molecular oxygen into ERF-VII Nt-Cys residues to form Cys-sulfinic acid (CSA), and that PCO activity is sensitive to oxygen availability. These enzymes therefore control ERF-VII stability and mediate the response to flood-induced hypoxia. I propose generating tools and knowledge to manipulate PCO activity, modulate CSA formation and stabilise ERF-VIIs. This is an attractive and tractable strategy to enhance stress tolerance in plants. The project will require (i) the development of efficient tools and assays to detect and quantify CSA, (ii) an understanding of the breadth of PCO activity for non-ERF-VII substrates, and (iii) an understanding of the role of non-enzymatic CSA formation. This knowledge will enable the development of effective and targeted mechanisms to manipulate PCO activity and improve stress tolerance.