MdIPT8, an isopentenyl transferase enzyme, enhances the resistance of apple to Colletotrichum gloeosporioides infection

Apple (Malus domestica) is a delicious fruit of high economic value. However, numerous destructive fungi affect apples, greatly limiting their production. Many studies have shown that salicylic acid and jasmonic acid improve plant resistance to fungal diseases, but the potential mechanisms of cytokinin action and fungal diseases remain largely unreported. The IPT gene family encodes the proteins required for cytokinin biosynthesis and plays a central role in plant biological progresses. In our previous study, we found that the disease resistance in autotetraploid apple was much better than 'Hanfu' diploid and analyzed the transcriptome data between 'Hanfu' diploid and autotetraploid apple. We found that the MdIPT8 gene was significantly differentially expressed. Therefore, we focused on gene family functions in cytokinin biosynthesis and biotic stress responses. We identified ten IPT genes in the 'Hanfu' whole genome that are unevenly distributed across the five apple chromosomes. Phylogenetic analysis indicated that this gene family belonged to two groups. Transcriptional analysis of the ten IPT genes indicated that MdIPT8 could be induced under Colletotrichum gloeosporioides infection in apple leaves. The MdIPT8 protein, when fused to the green fluorescent protein, identified the chloroplast as the site of protein localization. Finally, we confirmed that overexpression of MdIPT8 increased the resistance of C. gloeosporioides infection. Taken together, we have identified that the endogenous cytokinin content of 'Hanfu' leaves increased during C. gloeosporioides infection and the application of exogenous cytokinin improved the resistance of apple leaves to C. gloeosporioides and found that MdIPT8 can increase apple anthracnose resistance by improving the biosynthesis of cytokinin.