Pepper autophagy related gene CaATG8e differentially regulates plant tolerance to heat and salt stress

As a conserved protein degradation system, autophagy plays important roles in removing or degrading misfolded and denatured proteins to maintain the homeostasis in cells. As a core member of autophagy, the involvement of ATG8 in plant tolerance to abiotic stress is paid more attention. In this study, by the SMART online tool, the Atg8 conserved domain was detected in CaATG8e, and by the MEGA11 software, CaATG8e displayed closer phylogenetic relationship to the homologs from other Solanaceae species rather than another 4 CaATG8s members. The expression of CaATG8e was decreased after heat and salt stress treatments. When the expression of CaATG8e was silenced by virus induced gene silencing (VIGS) technique, the pepper seedlings presented improved tolerance to heat stress. Compared to those in control of TRV2:00, the accumulations of autophagosome punctate, H2O2, and dead cells, the increment of relative electrolyte leakage, and the decrement of chlorophyll content were reduced in TRV2:CaATG8e, while the enhancement of transcript level of CaHsfA2, CaHSP70.1, and CaHSP16.1 were strengthened. On the contrary, when CaATG8e was overexpressed by the method of floral dip, Arabidopsis displayed compromised tolerance to heat stress with the decreasing of the rate of green cotyledons and the chlorophyll content. However, CaATG8e had no obvious effects in the regulation of tolerance to salt stress in both pepper and Arabidopsis. These results suggest that CaATG8e negatively regulates the heat tolerance of pepper via increasing the H2O2 accumulations and suppressing the expression of HSR (heat shock response) related genes.