MdWRKY45 contributes to resistance against Botryosphaeria dothidea in apple

Malus domestica "Fuji" is the predominant apple cultivar grown around the world, but it is highly susceptible to apple ring rot caused by Botryosphaeria dothidea. WRKY transcription factors (TFs) play key roles in multiple physiological responses to plant defense. We have previously reported the involvement of several MdWRKY TFs in plant defense against. In this study, we identified a new MdWRKY TF, MdWRKY45, which is induced by B. dothidea infection. MdWRKY45 was localized in the nucleus and exhibited transcriptional activity. Overexpression of MdWRKY45 enhanced the resistance of transgenic apple calli and fruits to B. dothidea infection. Conversely, suppression of MdWRKY45 decreased the disease resistance of apple calli and fruits. Further transcriptome profiling and expression analysis showed that various genes regulating the release of salicylic acid (SA), jasmonic acid (JA), and reactive oxygen species (ROS) were either up-regulated or down-regulated in MdWRKY45-RNAi transgenic apple calli compared with wild-type (WT). During B. dothidea infection, MdWRKY45 modulated the levels of SA and JA, as well as ROS burst. Moreover, MdWRKY45 could bind to the W-box cis-element in the promoters of MdPR1, MdJAZ1, and MdRbohF genes, thereby regulating their expression. In conclusion, MdWRKY45 primarily confers resistance to B. dothidea infection through pathways involving SA, JA, and ROS burst defense.