Exogenous Calcium Improved Resistance to <i>Botryosphaeria dothidea</i> by Increasing Autophagy Activity and Salicylic Acid Level in Pear

Abstract

Pear ring rot, caused by <i>Botryosphaeria dothidea</i>, is one of the most serious diseases in pear. Calcium (Ca²⁺) was reported to play a key role in the plant defense response. Here, we found that exogenous calcium could enhance resistance to <i>B. dothidea</i> in pear leaves. Less H₂O₂ and O₂^- but more activated reactive oxygen species scavenge enzymes accumulated in calcium-treated leaves than in H₂O-treated leaves. Moreover, the increased level of more ascorbic acid-glutathione was maintained by Ca²⁺ treatment under pathogen infection. The expression of core autophagy-related genes and autophagosome formations were enhanced in Ca²⁺-treated leaves. Silencing of <i>PbrATG5</i> in <i>Pyrus betulaefolia</i> conferred sensitivity to inoculation, which was only slightly recovered by Ca²⁺ treatment. Moreover, the salicylic acid (SA) level and SA-related gene expression were induced more strongly by <i>B. dothidea</i> in Ca²⁺-treated leaves than in H₂O-treated leaves. Taken together, these results demonstrated that exogenous Ca²⁺ enhanced resistance to <i>B. dothidea</i> by increasing autophagic activity and SA accumulation. Our findings reveal a new mechanism of Ca²⁺ in increasing the tolerance of pear to <i>B. dothidea</i> infection.