MdATG8i functions positively in apple salt tolerance by maintaining photosynthetic ability and increasing the accumulation of arginine and polyamines

Abstract

Autophagy has been widely reported to play critical roles in plant adaption to various abiotic and biotic stressors. Although many studies have shown that autophagy-deficient mutants exhibit sensitivity to salt stress, our understanding of the detailed function of autophagy in response to salt stress remains limited. In this study, we found that the expression of MdATG8i was induced by salt stress. We treated transgenic apple plants overexpressing MdATG8i with salt stress, and explored its biological role in response to salt treatment. The results showed that the growth limitation, reactive oxygen species generation and Na+ accumulation caused by salt stress were alleviated in transgenic plants. The shrinkage of stomata and the damage to photosynthetic ability caused by salt stress were diff ;erentially mitigated. These changes were accompanied by the elevated autophagic activity and the accumulation of proline, arginine and its downstream polyamine products in two transgenic lines, which play important roles in plant tolerance to salt stress. In summary, these results revealed that MdATG8i-mediated autophagy enhanced salt tolerance in apple, primarily by alleviating the decrease in carbon assimilation and the accumulation of compatible osmolytes.