Abstract
BackgroundCorynespora cassiicola, as a necrotrophic phytopathogenic ascomycetous fungus, can infect hundreds of species of plants and rarely causes human diseases. This pathogen infects cucumber species and causes cucumber target spot, which has recently caused large cucumber yield losses in China. Genome sequence and spore germination-associated transcriptome analysis will contribute to the understanding of the molecular mechanism of pathogenicity and spore germination of C. cassiicola.ResultsFirst, we reported the draft genome sequences of the cucumber-sampled C. cassiicola isolate HGCC with high virulence. Although conspecific, HGCC exhibited distinct genome sequence differences from a rubber tree-sampled isolate (CCP) and a human-sampled isolate (UM591). The proportion of secreted proteins was 7.2% in HGCC. A total of 28.9% (4232) of HGCC genes, 29.5% (4298) of CCP genes and 28.6% (4214) of UM591 genes were highly homologous to experimentally proven virulence-associated genes, respectively, which were not significantly different (P = 0.866) from the average (29.7%) of 10 other phytopathogenic fungi. Thousands of putative virulence-associated genes in various pathways or families were identified in C. cassiicola. Second, a global view of the transcriptome of C. cassiicola spores during germination was evaluated using RNA sequencing (RNA-Seq). A total of 3288 differentially expressed genes (DEGs) were identified. The majority of KEGG-annotated DEGs were involved in metabolism, genetic information processing, cellular processes, the organismal system, human diseases and environmental information processing.ConclusionsThese results facilitate the exploration of the molecular pathogenic mechanism of C. cassiicola in cucumbers and the understanding of molecular and cellular processes during spore germination.
Highlights
Corynespora cassiicola, as a necrotrophic phytopathogenic ascomycetous fungus, can infect hundreds of species of plants and rarely causes human diseases
HGCC isolate features The HGCC isolate with high virulence to cucumber was selected for de novo sequencing of C. cassiicola sampled from cucumber
A total of 54,580,316 high-quality reads were assembled into 1032 scaffolds (N50: 500 kb) with a genome size of 42.7 Mb, which was slightly less than that of CCP (44.8 Mb) (JGI: 1019537) and greater than that of UM591 (41.4 Mb) (GenBank: JAQF00000000.1) (Table 1)
Summary
Corynespora cassiicola, as a necrotrophic phytopathogenic ascomycetous fungus, can infect hundreds of species of plants and rarely causes human diseases. This pathogen infects cucumber species and causes cucumber target spot, which has recently caused large cucumber yield losses in China. C. cassiicola, as a necrotrophic parasitic fungus, can infect more than 500 plant species, including tomato, eggplant, tobacco, rubber, cotton, soybean and balsam pear, in addition to cucumber and cause plant spot diseases [2], which have transitioned from minor to major diseases in the last half century. Some isolates with no Cas gene generated moderate symptoms on rubber tree leaves, showing that uncharacterized effectors existed in C. cassiicola [10]
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