Triticain alpha represents the major active papain-like cysteine protease in naturally senescing and ozone-treated leaves of wheat

Abstract

Current background tropospheric ozone (O₃) concentrations have significant adverse effects on wheat. O₃ generally induces oxidative damages and premature leaf senescence leading to important yield losses. As leaf protein degradation and recycling is involved in both maintaining cell longevity during abiotic stresses and performing efficient nitrogen remobilization during senescence, we aimed to identify proteases involved in acidic endoproteolytic activities during natural and O₃-induced leaf senescence in wheat. Field-grown plants of two winter wheat cultivars were exposed to ambient and semi-controlled chronic O₃ concentrations, from pre-anthesis to grain harvest. Yield parameters were impacted by the most elevated O₃ exposure for both cultivars. At the cellular level, our analysis revealed that both natural leaf senescence and O₃ treatments induced a stimulation of acidic (pH 5.5) endoproteolytic activities, mostly due to papain-like cysteine proteases (PLCPs). Identification of active PLCPs using activity-based protein profiling (ABPP) revealed that Triticain α was the major active PLCP in senescing flag leaves and the only PLCP whose abundance increased with O₃ stress, a result of positive transcriptional regulation. Our study provides novel insight into the implication of PLCP-mediated proteolysis in O₃ sensitivity in a major crop.