Ectopic expression of an autophagy-associated MdATG7b gene from apple alters growth and tolerance to nutrient stress in Arabidopsis thaliana

Plants are often subjected to unfavorable growing conditions, such as a limited supply of nutrients. Macroautophagy (autophagy) is an intracellular recycling process that targets unwanted proteins or damaged organelles, thus providing the nitrogen and carbon needed for survival and new plant growth during different phases of development and nutrient deprivation. During the formation of autophagosomes, AuTophaGy-related protein 7 (ATG7) is involved in both the ATG8 and ATG12 conjugation pathways. We isolated two ATG7 orthologs—MdATG7a and MdATG7b—from ‘Golden Delicious’ apple (Malus domestica Borkh.). Both were differentially responsive to leaf senescence, nitrogen depletion, and oxidative stresses at the transcriptional level. Heterologous expression of MdATG7b in Arabidopsis accelerated vegetative growth and facilitated the transition into reproductive phase, while also increasing the number of lateral branches, alleviating the negative effects of salt stress on seed germination and conferring tolerance to nitrogen- and carbon starvation. These results suggest that, as one of the important autophagy-related genes, MdATG7b enhances plant tolerance to nitrogen and carbon limitations, and it might be used as an important candidate for breeding crops with improved tolerance to nutrient-starvation stress.