Regulation of effector gene expression as concerted waves in Leptosphaeria maculans: a two-player game

Effectors are molecules secreted by the pathogen that facilitate infection of the host plant and establishment of the disease. These effectors are produced in concert during infection. However, little is known about how the expression of the genes encoding these effectors is regulated. As some of these genes are located in regions rich in repeated elements, the role of chromatin remodeling in their regulation has recently been studied, establishing in particular that the heterochromatin mark H3K9me3 (trimethylation of lysine 9 of histone 3), set up by the methyltransferase KMT1, was involved in controlling effector expression in several phytopathogenic fungi. However, this chromatin regulation alone did not explain the induction of effector expression at the time of infection, suggesting that a second level of regulation, probably involving a specific transcription factor, was required.

In Leptosphaeria maculans, a fungus of the Dothideomycetes family causing rapeseed crown necrosis, the researchers identified the ortholog of Pf2, a fungal-specific transcription factor belonging to the Zn2Cys6 family, described as essential for pathogenesis and the expression of effector-encoding genes. The researchers studied its role in conjunction with KMT1, by inactivating and overexpressing LmPf2 in a wild-type strain and in a mutant inactivated for KMT1. Functional and transcriptomic analyses of the corresponding transformants revealed an essential role for LmPf2 in the establishment of pathogenesis, and a major effect on the induction of effector expression once repression by KMT1 is lifted.

These results demonstrate, for the first time, the involvement of a dual control in fungal effector expression.

Contacts : jessica.soyer@inrae.fr et isabelle.fudal@inrae.fr