Both silencing- and over-expression of pepper CaATG8c gene compromise plant tolerance to heat and salt stress

Autophagy is well-known as a conserved survival mechanism that protects cells from adverse environments, and autophagy-related protein 8 (ATG8) plays a key role in autophagy process as an, essential component. However, the contribution of ATG8 to plant tolerance to environmental stresses is ambiguous. To gain insight into whether and how ATG8 gene functions in plant adaptation to adverse environment conditions, we characterized an ATG8 gene CaATG8c from pepper (Capsicum annuum L.), and found that the deduced amino acid sequence of CaATG8c gene contained the conserved necessary domains and residue for ATG8 functions. Under normal condition, the expression of CaATG8c was detected in all pepper tissues/organs, and its subcellular expression was located to the cytoplasm in onion epidermal cells. The silencing-expression of CaATG8c rendered pepper seedlings more sensitive to heat and salt stress by aggravating the chlorophyll degradation, MDA accumulation and SOD activity decrease. Unexpectedly, the over-expression of CaATG8c gene also reduced Arabidopsis tolerance to heat and salt stress by inhibiting the growth of primary roots and the generation of secondary roots, and disturbing the expression of stress response genes. Our results suggested that both silencing- and over-expression of CaATG8c gene conferred plants more sensitivity to heat and salt stress. Furthermore, the possible mechanism for CaATG8c silencing is speculated to the reduced ability to remove accumulated ROS, whereas for gene over-expression, it is supposed to the disturbance of ROS signal. We propose that the stable and timely expression of CaATG8c may be important for plant adaption to adverse environments.