CRISPR/Cas9-Mediated Mutagenesis of in Apple Callus and VIGS-Mediated Silencing of in Fruits Improve Resistance to .

Cyclic nucleotide-gated ion channels (CNGCs) have been reported to be involved in multiple plant physiological processes. Their involvement in plant immunity has been studied in several herbal plant species. It remains unclear whether CNGCs in woody plants play a similar role in plant immunity. In the present study, we identified an apple CNGC (designated as MdCNGC2), which is the homolog of CNGC2. Analysis of tissue distribution revealed that was expressed in all tested tissues. Abundant transcripts of were observed in leaves and shoot bark. Low expression was observed in fruits and roots. expression was induced in apple callus and shoot bark by . The induction of was significantly higher in susceptible cultivars "Fuji," "Ralls Janet," and "Gala" compared to the resistant cultivar "Jiguan," suggesting that MdCNGC2 may be a negative regulator of resistance to . mutagenesis mediated by gene editing based on the CRISPR/Cas9 system led to constitutive accumulation of SA in apple callus. A culture filtrate of (BCF) induced the expression of several defense-related genes including , , , , , and . Moreover, the induction of these genes was significantly higher in mutant (MUT) callus than in wild type (WT) callus. Further analysis showed that the spread of was significantly lower on MUT callus than on WT callus. Knockdown of the gene reduced lesions caused by in apple fruits. These results collectively indicate that is a negative regulator of resistance to in apple callus.