Whole genome and transcriptome analysis reveal adaptive strategies and pathogenesis of Calonectria pseudoreteaudii to Eucalyptus.

BACKGROUND

Leaf blight caused by Calonectria spp. is one of the most destructive diseases to affect Eucalyptus nurseries and plantations. These pathogens mainly attack Eucalyptus, a tree with a diversity of secondary metabolites employed as defense-related phytoalexins. To unravel the fungal adaptive mechanisms to various phytoalexins, we examined the genome of C. pseudoreteaudii, which is one of the most aggressive pathogens in southeast Asia.

RESULTS

A 63.7 Mb genome with 14,355 coding genes of C. pseudoreteaudii were assembled. Genomic comparisons identified 1785 species-specific gene families in C. pseudoreteaudii. Most of them were not annotated and those annotated genes were enriched in peptidase activity, pathogenesis, oxidoreductase activity, etc. RNA-seq showed that 4425 genes were differentially expressed on the eucalyptus(the resistant cultivar E. grandis×E.camaldulensis M1) tissue induced medium. The annotation of GO term and KEGG pathway indicated that some of the differential expression genes were involved in detoxification and transportation, such as genes encoding ABC transporters, degrading enzymes of aromatic compounds and so on.

CONCLUSIONS

Potential genomic determinants of phytoalexin detoxification were identified in C. pseudoreteaudii by comparison with 13 other fungi. This pathogen seems to employ membrane transporters and degradation enzymes to detoxify Eucalyptus phytoalexins. Remarkably, the Calonectria genome possesses a surprising number of secondary metabolism backbone enzyme genes involving toxin biosynthesis. It is also especially suited for cutin and lignin degradation. This indicates that toxin and cell wall degrading enzymes may act important roles in the establishment of Calonectria leaf blight. This study provides further understanding on the mechanism of pathogenesis in Calonectria.