MdNHL8, an NDR1/HIN1-like Gene, Enhances Resistance Against Apple Ring Rot

Apple ring rot, caused by Botryosphaeria dothidea, represents a major challenge for apple cultivation worldwide. However, the genetic factors that confer resistance in apples are not well understood. This study utilized time-series transcriptome profiling, combined with weighted gene co-expression network analysis and previously identified quantitative trait loci, leading to the identification of MdNHL8 as a candidate gene linked to resistance. A genome-wide examination of the apple NDR1/HIN1-like gene family revealed 57 members with diverse conserved domains, confirming that MdNHL8 features a distinct RBR-type E3 ligase domain. Subcellular localization experiments showed that MdNHL8 is localized in the nucleus and plasma membrane. Functional assays indicated that overexpression of MdNHL8 enhances resistance to apple ring rot and significantly elevates the expression of MdPR1, whereas silencing this gene does not enhance resistance and exhibits a trend toward increased susceptibility. Furthermore, additional transcriptome sequencing analysis of MdNHL8 transgenic calli highlighted a turquoise module closely linked to MdNHL8-mediated resistance, identifying MdCYCB3, MdEIX2, and MdABC4 as candidate downstream genes with expression patterns tightly correlated with MdNHL8. This research identifies MdNHL8 as a positive regulator in apple defense against B. dothidea and provides a basis for further exploring the regulatory network centered on MdNHL8 in disease resistance, offering insights for future breeding efforts aimed at enhancing resistance to apple ring rot.