StructuraLEP

Fungi are the most devastating pathogens of plants, including crops of major economic importance and have a significant impact in economics, human health and environment. In addition, fungi show an incredible plasticity and ability to disseminate and adapt rapidly to drastic changes in their environment. These processes of adaptation are exemplified by Leptosphaeria maculans which is an Ascomycete responsible for an economically important disease of oilseed rape, behaves as an invasive species and shows an extremely high evolutionary potential. Control of fungal crop diseases necessitates a global understanding of fungal pathogenicity determinants. During infection, pathogens, including fungi, secrete an arsenal of molecules, collectively called effectors, key elements of pathogenesis which modulate innate immunity of the plant and facilitate infection. Effectors have a dual role in microbe-plant interactions, both targeting plant components and being targeted by resistance (R) proteins and then termed avirulence (AVR) proteins. Fungal effector genes are very diverse and typically encode small proteins, predicted to be secreted (SSPs, Small Secreted Proteins), with no or low homology in databases, and absence of known motif. As such their function or role in pathogenesis is mostly unknown and structure information provides an elegant way to resolve functional traits. From a limited set of data, the patterns that begin to emerge for possible fungal effector functions include interference with plant immunity, inhibition of programmed cell death, neutralization of host defence molecules and debilitation of plant tissues. On these bases, we propose a basic research project, StructuraLEP, to elucidate the involvement of L. maculans effectors in pathogenicity. We want to reach this objective through the structural and functional characterization of a few major effector proteins and the determination of their interactants. StructuraLEP is an interdisciplinary project involving two teams with internationally acknowledged expertise in the complementary fields of fungal genomics / fungal effector biology (Partner 1) and structural biology (Partner 2). We will investigate six L. maculans effectors corresponding to promising candidates previously identified by Partner 1 and chosen for their biological significance (involvement in fungal fitness, cognate R gene identified) or because they may represent novel modes of interaction with their plant target (two AVR genes necessary to be recognized by a specific R gene). The StructuraLEP project will combine structural biology, functional genomics, plant transformation and cytology and is organised in 3 main tasks (plus one coordination task) ranging from an initial task aiming to structurally and functionally characterise L. maculans effectors (Task 2), an exploratory task that relies on the screening of plant proteins and molecules potentially interacting with L. maculans effectors (Task 3) to a more focused task aiming to functionally and physically understand the identified interactions (Task 4). The effectors and their interactants will be analysed according to these complementary approaches to address the following questions: (i) What is the 3-D structure and the associated biochemical function of L. maculans effectors? (ii) Where do L. maculans effectors act during plant infection? (iii) Which molecules interact with L. maculans effectors? and (iv) Which plant processes are manipulated and which host proteins are targeted by L. maculans effectors? Integration of knowledge on effector 3-D structure, localization, targeting of host proteins and host processes by L. maculans effectors studied in the StructuraLEP project will give insight into the fundamental processes governing the close association of a pathogenic fungus with its host plant. Progresses in these fields are necessary for sustainable crop production through the development of novel strategies to control fungal diseases.