Two cowpea Rubisco activase isoforms for crop thermotolerance

 A vital crop for sub-Saharan Africa, cowpea productivity is threatened by climate change, including increased heatwave intensity, duration, and frequency. Rubisco activase (Rca) is a key molecular chaperone that maintains Rubisco activity and due to its thermal sensitivity is a key target for improving crop climate resilience. We identified and characterised four Rca isoforms in Vigna unguiculata (L.) Walp. cv. IT97K-499-35 in vitro: Rca1β, Rca8α, Rca10α and Rca10β. Cowpea leaf and plant growth traits were also investigated during a 5-day +10 °C heatwave that included assessment of Rubisco and Rca activity in leaf extracts, and relative changes in the abundance of the four Rca isoforms. Cowpea Rca10α and Rca10β had higher thermal maxima, broader thermal optima and higher rates of ATP hydrolysis and Rubisco reactivation in vitro. In the absence of water deficit, the heatwave caused only mild effects, including increases in leaf temperature and expression of Rca10, small decreases in Rubisco activity and activation state, and unaltered temperature response of Rubisco activation by Rca.  The superior Rca10α and Rca10β isoforms offer the prospect of enhancing the thermotolerance of cowpea and other crops in anticipation of more extreme future heatwaves.