Overexpression of MdATG18a in apple improves resistance to Diplocarpon mali infection by enhancing antioxidant activity and salicylic acid levels

Abstract

Marssonina apple blotch, caused by <i>Diplocarpon mali</i>, is one of the most serious diseases of apple. Autophagy plays a key role in pathogen resistance. We previously showed that MdATG18a has a positive influence on drought tolerance. Herein, we describe how overexpression (OE) of <i>MdATG18a</i> enhances resistance to <i>D. mali</i> infection, probably because less H₂O₂ but more salicylic acid (SA) is accumulated in the leaves of OE apple plants. Expression of <i>chitinase</i>, <i>β-1,3-glucanase</i>, and SA-related marker genes was induced more strongly by <i>D. mali</i> in OE lines. Transcript levels of other important <i>MdATG</i> genes were also drastically increased by <i>D. mali</i> in OE plants, which indicated increased autophagy activities. Taken together, these results demonstrate that OE of <i>MdATG18a</i> enhances resistance to infection by <i>D. mali</i> and plays positive roles in H₂O₂-scavenging and SA accumulations. Our findings provide important information for designing strategies which could induce autophagy to minimize the impact of this disease on apple production.