A TIR-NBS-LRR Gene Regulates Resistance to Glomerella Leaf Spot in Apple.

Glomerella leaf spot (GLS), caused by the fungus , is one of the most devastating apple diseases. Our previous study reported that the GLS resistance locus was defined on the chromosome 15 region. Here, we further found a single-nucleotide polymorphism (SNP) site (SNP) in the GLS resistance that was able to distinguish resistant cultivars (lines) from susceptible ones. On the basis of the SNP site, we cloned a TNL gene from the GLS resistant locus and named it (NCBI Accession Number: ON402514). This gene contains a toll/interleukin-1 receptor transmembrane domain (TIR), nucleotide-binding sites (NBS), and leucine-rich repeat (LRR) domain. Subcellular location indicated that MdTNL1 was expressed in the nucleus and cell membrane. Ectopic overexpression of in caused cell death. We further demonstrated allelic polymorphisms in . It is noteworthy that NBS and LRR domains of the MdTNL1 protein serve as the repository for generating allelic diversity. Quantitative real-time PCR (qRT-PCR) assay revealed that was highly expressed in resistant apple cultivar 'Fuji' after inoculation with whereas susceptible cultivar 'Golden Delicious' exhibited low expression after inoculation. Over-expression of in susceptible apple fruits and leaves improved disease resistance, while in 'Orin' calli, silencing the gene conversely decreased GLS resistance. In conclusion, we identified a GLS associated with SNP and demonstrated that a TIR-NBS-LRR gene positively regulates GLS resistance in apple.