Multifarious roles of the smallest Arabidopsis thaliana MAPKKKs clade (MAPKKK19, 20 and 21) as an integrative hub for plant pathogen interactions, growth, development and 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 signaling 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, localization of a protein or its half-life, leading to major changes in cell homeostasis. The protein kinase family exemplifies such a major group of signaling proteins. Kinases are enzyme that modifies other proteins by chemically adding a phosphate groups 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 leads to the writer-reader-eraser triad of phosphorylation based signaling. 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 kinase's 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 humans, nematodes, 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 signaling. Our current research program focuses on multiple aspects of cell-cell communication, from plant reproduction to the role of signaling cascades involving protein kinases in gametophytes development, e.g., the embryo sac of the ovule and the pollen, and in plant innate immunity. In this research project, we focus on the role of a newly assembled MAPK cascade that affects numerous aspects of the life of a plant, e. g., growth, sexual reproduction, and diseases (plant innate immunity) as determined by the analysis of mutant plants lacking these kinases.