Linking cell wall dynamics to ABA homeostasis: polyamines and pectin fragments as cell wall invertase stimulators

Plants are continuously exposed to various biotic and abiotic stresses, and the phytohormone ABA fulfils a central role during these responses. Below and above certain ABA levels, normal plant growth and development is negatively affected. "Priming" with certain exogenous substances (e.g. sugars, polyamines) prepares plants to react more efficiently during subsequent stresses. The regulation of intracellular ABA concentrations (ABA homeostasis) during "priming" and stress responses is poorly understood. Here, a working model is proposed linking cellular ABA homeostasis to cell wall invertase (CWI) activity through ABA-mediated invertase inhibitor (INH) production, with the fine-tuning of INH binding to CWI mediated by various extracellular factors (polyamines, pectin fragments, salt etc.). This working model will be evaluated by a combination of in vitro and in vivo experiments on sink and leaf source tissues in the context of abiotic and biotic stress. Wild-type plants and mutant/transgenic plants affected in INH and ABA biosynthesis will be compared. The involvement of lipid signaling and/or endocytosis during "priming" will also be investigated. Overall, this project will not only increase our fundamental knowledge on the underlying mechanisms during “priming” and (a)biotic stress responses, but may also contribute to develop cheap and natural alternatives to toxic agrochemicals - important for sustainable agriculture.