High-Quality Assembly of the Apple Fungal Pathogen Marssonina coronaria Genome and Functional Analysis of Candidate Effectors

<i>Marssonina coronaria</i> is the causal agent of apple blotch, which poses a significant threat to apple production worldwide. Here, Illumina and Oxford Nanopore sequencing were combined to generate a high-quality <i>M. coronaria</i> YL1 genome assembly (54.5 Mb, 23 contigs). Based on genome annotation, 97 candidate effector proteins (CEPs) were identified, and 61 CEPs were successfully cloned for functional analysis. Transient expression assays in <i>Nicotiana benthamiana</i> revealed that eight CEPs significantly suppressed BAX-induced cell death, with McCEP12, McCEP23, McCEP24, and McCEP52 concurrently inhibiting flg22-triggered reactive oxygen species bursts. Two signal peptide-dependent cell death-inducing effectors were identified: McNLP1, containing an NPP1 domain, and McCEP3. McCEP3 exhibited evolutionary conservation within Ascomycota, with its homologous gene <i>VmMcCEP3</i> from <i>Valsa mali</i> inducing cell death in <i>N. benthamiana</i>. McEP03-triggered cell death was independent of BAK1/SOBIR1 receptor kinases. This study provides a high-quality genomic resource for <i>M. coronaria</i> and sheds light on the mechanisms by which its CEPs modulate host immunity, offering new insights into the molecular interactions between the pathogen and its host.