Different waves of effector genes with contrasted genomic location are expressed by Leptosphaeria maculans during cotyledon and stem colonisation of oilseed rape
J. GERVAIS (1), T. Rouxel (1), M. Balesdent (1), I. Fudal (1), C. Plissonneau (1) (1) INRA BIOGER, France

Leptosphaeria maculans, causal agent of blackleg disease, colonises oilseed rape (Brassica napus) in two stages: a short and early colonisation stage corresponding to cotyledon or leaf colonisation leading to leaf spot development, and a late colonisation stage during which the fungus colonises systemically and symptomlessly the plant during several months before stem canker appears. To date, determinants of the late colonisation stage are poorly understood; L. maculans may either successfully escape plant defences leading to the stem canker development, or the plant can develop an “adult-stage” resistance reducing canker incidence. Here, we hypothesized that L. maculans deploys effectors different from the one deployed in the early colonisation to enable the long symptomless stem colonisation. To get insight into these determinants, we performed a RNA-seq pilot project comparing fungal gene expression in infected cotyledons and in infected stems. Despite the low fraction of fungal material in infected stems with or without symptoms, enough fungal transcripts were detected to conduct a RNA-seq analysis focused on effector genes. With this approach 175 late effector candidates, under-expressed in the early colonisation stage and over-expressed in the infected stems, were identified. These new effector genes, putatively involved in the systemic colonisation, are located in gene-rich genomic regions, whereas the early effector genes involved in cotyledon colonisation are located in gene-poor regions of the genome. Our analysis reveals a link between the expression pattern of effectors and their genomic location.

Abstract Number: C2-5, P11-391
Session Type: Concurrent