Climate changes such as heat waves often affect plant growth and pose a growing threat to natural and agricultural ecosystems. Elevated atmospheric CO can mitigate the negative effects of heat stress, but the underlying mechanisms remain largely unclear. We examined the interactive effects of elevated CO (eCO ) and temperature on the generation of the hydrogen peroxide (H O ) and stomatal movement characteristics associated with heat tolerance in tomato seedlings grown under two CO concentrations (400 and 800 µmol mol ) and two temperatures (25 and 42°C). eCO ameliorated the negative effects of heat stress, which was accompanied by greater amounts of RESPIRATORY BURST OXIDASE 1 (RBOH1) transcripts, apoplastic H O accumulation and decreased stomatal aperture. Silencing RBOH1 and SLOW-TYPE ANION CHANNEL, impeded eCO -induced stomatal closure and compromised the eCO -enhanced water use efficiency as well as the heat tolerance. Our findings suggest that RBOH1-dependent H O accumulation was involved in the eCO -induced stomatal closure, which participate in maintaining balance between water retention and heat loss under eCO concentrations. This phenomenon may be a contributor to eCO -induced heat tolerance in tomato, which will be critical for understanding how plants respond to both future climate extremes and changes in CO .

Phytosulfokine (PSK) is a danger-associated molecular pattern recognized by PHYTOSULFOKINE RECEPTOR 1 (PSKR1), and initiates intercellular signaling to coordinate different physiological processes, especially in the defense response to the necrotrophic fungus Botrytis cinerea. The activity of peptide receptors is largely influenced by different posttranslational modifications, which determines intercellular peptide signal outputs. To date, the posttranslational modification to PSKR1 remains largely unknown. Here, we show that tomato (Solanum lycopersicum) PSKR1 is regulated by the ubiquitin/proteasome degradation pathway. Using multiple protein-protein interaction and ubiquitylation analyses, we identified that plant U-box E3 ligases PUB12 and PUB13 interacted with PSKR1, among which PUB13 caused PSKR1 ubiquitylation at Lys-748 and Lys-905 sites to control PSKR1 abundance. However, this posttranslational modification was attenuated upon addition of PSK. Moreover, the disease symptoms observed in PUB13 knock-down and overexpression lines demonstrated that PUB13 significantly suppressed the PSK-initiated defense response. This highlights an important regulatory function for the turnover of a peptide receptor by E3 ligase-mediated ubiquitylation in the plant defense response.