Genome-wide identification of candidate secretory effector proteins of Colletotrichum tanaceti isolated from Australian pyrethrum

Colletotrichum tanaceti is a foliar fungal pathogen causing anthracnose in pyrethrum; the source plant of the natural insecticide compounds, pyrethrins. The molecular determinants of pathogenesis of C. tanaceti to pyrethrum are unknown. Fungal effectors are small secreted proteins driving virulence by manipulating the host response. The objective of this study was to examine the genome of C. tanaceti to detect Candidate Secreted Effector Proteins (CSEPs). We report the first draft genome assembly of C. tanaceti using Illumina MiSeq platform and annotation supported by RNASeq of saprobic and biotrophic stages. The genome comprises 5,245 contigs, an estimated size of 58Mb with 96% BUSCO completeness. A deduced proteome of 12,051 proteins were used for downstream prediction of the secretome. In-silico analysis pipeline was used to predict the signal peptides, followed by the exclusion of membrane proteins and endoplasmic reticulum targets, to define a secretome of 1,185 proteins. These proteins were used to predict 224 CSEPs, of which 189 lacked Pfam domains. The candidates were further screened for known conserved motifs of effectors and similarity to known effectors. A total of 33 CSEPs with no orthologs in 19 related species and no Pfam domains, were presumed to be C. tanaceti-specific. These effector candidates can be utilized for investigating their biological function in pathogenesis and for breeding of pyrethrum for resistance.