CaARR2 interacts with CaLBD24 to synergistically mount high-temperature specific immunity against Ralstonia solanacearum by activating genes including CaRPT2

Abstract It has been previously found that pepper (Capsicum annuum) activates high-temperature specific immunity against R. solanacearum in cytokinin signalling dependent manner at high temperature (37°C), while how this high-temperature specific immunity is activated remain unclear. Herein, we demonstrate that both CaARR2 and CaLBD24 acted positively in pepper immunity against R. solanacearum infection at 37°C but not at 28°C. CaLBD24 was found to interact in the nuclei with CaARR2, which is otherwise present in plastids upon R. solanacearum infection at 28°C but translocated into the nuclei upon 37°C exposure alone, R. solanacearum infection at 37°C or the exogenous application of ABA or R. solanacearum infection at 28°C combined with exogenous application of tZ. By ChIP-seq combined with RNA-seq assay, the CaARR2-CaLBD24 module in the nuclei was further found to activate high temperature specific immunity by directly co-targeting and activating genes including CaRPT2 via binding their corresponding cis-elements, and CaRPT2 was further found by virus gene silencing to act positively in pepper immunity against R. solanacearum at 37°C. In addition, CaARR2, CaLBD24 and CaRPT2 ware also found to act positively in defense response of tomato R. solanacearum infection at 37°C. The results uncover that high-temperature specific immunity is activated in pepper and tomato in cytokinin signalling dependent manner using ARR2-LBD24 module to activate genes including RPT2, providing new insights into mechanism underlying bacterial wilt resistance in pepper and tomato at high temperatures.