Genome wide transcriptome profiling of Fusarium oxysporum f sp. ciceris conidial germination reveals new insights into infection-related genes

Abstract

Vascular wilt caused by Fusarium oxysporum f. sp. ciceris (Foc) is a serious disease of chickpea (Cicer arietinum L.) accounting for approximately 10-15% annual crop loss. The fungus invades the plant via roots, colonizes the xylem vessels and prevents the upward translocation of water and nutrients. Infection is initiated by conidia that invade the host tissue often by penetration of intact epidermal cells. Here, we report the characterization of the transcriptome of Foc sequenced using Illumina Hiseq technology during its conidial germination at different time points. Genome-wide expression profiling revealed that genes linked to fungal development are transcribed in successive ways. Analysis showed that Foc have large sets of germination-related genes and families of genes encoding secreted effectors, cell wall/pectin-degrading enzymes, metabolism related enzymes, transporters and peptidases. We found that metabolism related enzymes are up-regulated at early time point whereas most transporters and secondary metabolites important for tissue colonization and pathogenicity are up-regulated later as evident from the qRT-PCR. The study demonstrated that early conidial germination in Foc is accompanied by rapid shifts in gene expression that prepare the fungus for germ tube outgrowth, host cell invasion and pathogenesis. This work lays the foundation for facilitating further research towards understanding this host-pathogen interaction.

Figure 1. Microscopic examination of conidial germination at different time points.

(a) 0 h- resting conidia. (b) 2 h-initiation of hyphal swellings (c) 6 h- emergence of germ tube. (d) 24 h- hyphal elongation and branching.

Figure 2. Differentially regulated transcripts with significant expression represented by log₂fold change ≥2 and ≤2 at various time points.

X-axis represents numbers of up-regulated and down-regulated transcripts, Y-axis represents six combinations of time points.

Figure 3. Functional classification of differentially expressed transcripts of Foc based on gene ontology (GO) as cellular component, molecular function and biological process.

Figure 4. Heat map showing up-regulated transcript (log2fold ≥ 2) common in four time points.

Genes with specific functions were labeled with blue dot and corresponding gene names with biological functions were listed in Table 2.

Figure 5. Pathways mapped with up-regulated transcripts at different combinations of time points.

Figure 6. Schematic representation of major biochemical pathways up-regulated during conidial germination.