Antagonistic Regulation by CPN60A and CLPC1 of TRXL1 that Regulates MDH Activity Leading to Plant Disease Resistance and Thermotolerance

Global warming and emerging plant diseases challenge agricultural food/feed production. We identify mechanism(s) regulating both plant thermotolerance and disease resistance. Using virus-induced gene silencing (VIGS)-based genetic screening, we identify a thioredoxin-like 1 (TRXL1) gene involved in plant nonhost disease resistance and thermotolerance. TRXL1 is reduced, partly degraded via proteases and proteasome, and alters its chloroplast localization during heat stress. TRXL1 interacts with more than 400 proteins, including chaperonin CPN60A, caseinolytic protease (CLPC1), and NADP-dependent malate dehydrogenase (NADP-MDH). Chaperonin 60A (CPN60A) guards TRXL1 from degradation, whereas CLPC1 degrades TRXL1 during heat stress. TRXL1 regulates NADP-MDH activity, leading to an increase in malate level and inhibition of superoxide radical formation. We show that CPN60A and NADP-MDH positively regulate nonhost resistance, and CPN60A positively and CLPC1 negatively regulate thermotolerance. This study shows an antagonistic post-translational regulation of TRXL1 by CPN60A and CLPC1 and regulation of MDH by TRXL1, leading to plant disease resistance and thermotolerance.