Apoplastic communication and metabolic fluxes in multipartite interactions
The apoplast has crucial functions in plant biology; it mediates communication with other cells and with the environment. Structurally, the apoplast is formed by the continuum of cell walls of adjacent cells and the extracellular spaces, thereby forming a tissue-level compartment. The apoplast matrix contains many enzymatic and nonenzymatic components, including solutes (e.g., ions, sugars, amino acids, phenolic compounds, and organic acids), proteins (e.g., extensins, peroxidases, and hydrolases), and cell-wall constituents (e.g., celluloses, pectin, and glycoproteins). During root colonization, plants and microbes secrete a number of proteins to the apoplast that are important for the outcome of the interaction. In this compartment fungal and plant enzymes converge to a common metabolic network integral to plant growth, development, and immunity. In this project, we will combine genetic, biochemical, metabolic, and cytological approaches in cooperation with RA4 and RA1 to (i) determine apoplastic metabolic fluxes in multipartite interactions; (ii) construct metabolic models for this apoplastic compartment with a focus on carbohydrate, purine and iron metabolism, to understand its role in the establishment and function of plant-microbe interactions; (iii) construct apoplastic and cell wall/apoplast-targeted sugar, purine and iron sensors to monitor root nutritional status over time during multipartite interactions. Putative microbial and plant key regulators will be analyzed by the use of beneficial and root pathogenic fungi. Specifically we will use Serendipita indica a beneficial fungal endophyte that colonizes the root of important crop plants such as barley (Hordeum vulgare) and Bipolaris sorokiniana, an aggressive pathogen of barley. In a previous study from our lab, several plant and fungal enzymes involved in nucleotide and sugar metabolic processes were detected in the root apoplastic fluids of barley during the colonization of S. indica (Nizam et al., EMBO report, 2019). The presence of these enzymes suggests that extracellular purine and carbohydrate metabolism are important during plant-fungal interactions. Although extensive studies have been performed on the carbohydrate metabolic process (CMP) associated with the microbial structural cell wall polymers such as chitin and peptidoglycan, the CMP associated with the fungal-derived polysaccharide matrix (PM) has not been studied so far during bipartite or multipartite plant-microbe interactions.
In the CEPLAS program, I aim to determine the fluxes associated with carbohydrates and nucleotides in the apoplast with a special focus during multipartite interactions. The outstanding questions which I would like to address are:
Expected outcome: This project will achieve a comprehensive and critical understanding of metabolic activity and signaling in the extracellular matrix during root colonization by different fungi.