Defining the dynamic interplay of a MAPK signaling cascade involved in plant growth, development and sexual reproduction.

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Communication and information transfer is everything, not only for our day-to-day lives but also for each and every cell of an organism. Information transfer in cells is better known as signal transduction. Numerous elements take part in cellular signalling and generally act through cascades that mediate sensing and processing of stimuli. These molecular circuits precisely detect, amplify, and integrate external signals to generate downstream responses. Thus, perception of a stimulus can lead to changes in gene expression, enzyme activity, localisation of a protein or its half-life, leading to major changes in cell homeostasis. The protein kinase family exemplifies such a major group of signalling proteins. Kinases are enzyme that modifies other proteins by chemically adding a phosphate group to specific amino acids, the most prevalent targets being serine, threonine and tyrosine. How can such a small modification exert profound effects on proteins? Because phosphorylated amino acids in proteins act as new entities, modifying the chemical nature of the protein’s surface, thereby enabling the formation of new protein-protein interactions. Why is it so widely used? Because it is reversible: the kinase adds a phosphate group on a substrate - this modifies the substrate’s properties, which in turn influence its interaction potential - then a phosphatase can remove the phosphate group. This lead to the writer-reader-eraser triad of phosphorylation based signalling. Phosphorylation as a means of communication seems to be even more important in sessile organisms like plants that cannot flea danger or adverse environmental conditions. This can be illustrated by the contribution of the protein kinases family in plants, which represent a much larger fraction of the proteome (the protein ensemble of an organism) compared to other eukaryotes. For example, in the plant model species Arabidopsis thaliana, kinases represent 4% of the proteome compared to ~2% in human, nematode, fruit fly or brewer’s yeast. Of these, two major families, the receptor kinase (RK) family (>600) and the MAPK (Mitogen-Activated Protein Kinases) superfamily (>100), account for 70% of all Arabidopsis protein kinases. Kinases are thus at the forefront of signalling. Our overall research program has been focusing on multiple aspects of cell-cell communication, from pollen-pistil interactions to the role of signalling cascades involving protein kinases in gametophytes development, e.g., the embryo sac of the ovule and the pollen. In this research project, we will focus on the role of a newly assembled MAPK cascade that affects plant growth, development and sexual reproduction, as determined by the analysis of mutant plants lacking these kinases. Using a wide range of experimental approaches, encompassing cell and molecular biology, biochemistry, molecular genetics, genomics, proteomics, and next generation sequencing, we will dissect the functioning of this signalling cascade that includes three kinases: a MAP kinase kinase kinase (or MKKK) that phosphorylate and activates a MAP kinase kinase (or MKK) that in turn phosphorylates a MAP kinase (MAPK or MPK) which then can modulate downstream effectors. These effectors will also be sought in order to better define the involvement of this signalling cascade in the aforementioned biological processes. Our goal is to decipher modules that will be helpful in fundamental, biotechnological, and applied aspects of the plant sciences. Considering that less than five complete MAPK signalling cascades (MKKK-MKK-MPK) have been characterized in plants, our research project will undoubtedly make significant contributions to the field and lead to the creation of tools that can be applied to crop production, protection and breeding.