Candidate genes expression profiling during wilting in chickpea caused by Fusarium oxysporum f. sp. ciceris race 5

Abstract

Chickpea production may be seriously threatened by Fusarium wilt, a disease caused by the soil-borne fungus Fusarium oxysporum f. sp. ciceris. F. oxysporum race 5 is the most important race in the Mediterranean basin. Recently, the region responsible for resistance race 5 has been delimited within a region on chromosome 2 that spans 820 kb. To gain a better understanding of this genomic region, we used a transcriptomic approach based on quantitative real-time PCR to analyze the expression profiles of 22 selected candidate genes. We used a pair of near-isogenic lines (NILs) differing in their sensitivity to Fusarium race 5 (resistant vs susceptible) to monitor the transcriptional changes over a time-course experiment (24, 48, and 72 hours post inoculation, hpi). Qualitative differences occurred during the timing of regulation. A cluster of 12 genes were induced by the resistant NIL at 24 hpi, whereas a second cluster contained 9 genes induced by the susceptible NIL at 48 hpi. Their possible functions in the molecular defence of chickpea is discussed. Our study provides new insight into the molecular defence against Fusarium race 5 and demonstrates that development of NILs is a rich resource to facilitate the detection of candidate genes. The new genes regulated here may be useful against other Fusarium races.

Fig 1. Cross-sectioned stems after six weeks of inoculation.

(A) Resistant line to Fusarium race 5 (RIP8-94-5). (B) Susceptible line to Fusarium race 5 (RIP8-94-11).

Fig 2. Hierarchical clustering analysis.

(A) The heatmap was constructed using the log2-transformed expression levels. Columns represent sample comparisons, while rows represent candidate genes. Colour scale, representing log2 expression differences between inoculated/non-inoculated plants, is shown in the bar. R and S represent resistant and susceptible NILs; 24, 48 and 72 represent hours after inoculation. (B) Expression profiles of differentially expressed genes peaked at 24 hpi in roots of the resistant genotype. (C) Expression profiles of differentially expressed genes peaked at 48 hpi in roots of the susceptible genotype. The mean expression average of each cluster is shown in black.

Fig 3. Expression profile of candidate genes in roots of chickpea over the time-course experiment.

Red line shows the averaged expression level in resistant NILs, whereas blue line describes the averaged level in the susceptible NILs.