Integrated Roles of Carbohydrates and CAZymes in Plant Health, Stress Resilience and Microbial Interactions

Plant structural and non-structural carbohydrates are central to plant health, growth, development and yield. Under optimal conditions, structural carbohydrates are major cell wall components that, together with lignin, protect plants from biotic and abiotic stress. Non-structural carbohydrates are essential for energy generation and are also converted into secondary metabolites or their precursors. Carbohydrate catabolic and oxidation processes produce metabolites such as amino acids, phenolics, flavonoids and organic acids, which contribute to overall plant health and development. Plant growth and development also require modification of the cell wall during extension — the “creep” process — facilitated by expansins and carbohydrate-active enzymes (CAZymes).Upon attack by fungi or pests, or exposure to abiotic stress such as drought or heat, plants reprogram carbohydrate metabolism and remodel the cell wall. This stress-induced reprogramming can cause a shortage of precursor molecules for cell wall biosynthesis, increasing susceptibility to biotic or abiotic stress. When carbohydrates are instead diverted to reinforce the cell wall, structural changes occur, including increased callose deposition. Deposition of cell wall polymers at the site of biotic stress drives papillae formation that blocks the pathogen or pest’s access to cytoplasmic contents. Under abiotic stress, oxidation of soluble carbohydrates is linked to a rapid increase in lignin precursor molecules required for lignin synthesis through the phenylpropanoid pathway. The interplay between the energy-generating function of soluble carbohydrates and their conversion into precursors for cell wall remodelling remains underexplored, hindering our understanding of cell wall modifications during biotic and abiotic challenges.Both structural and non-structural carbohydrates also regulate plant–beneficial microbe interactions. To date, efforts have focused on the plant cell wall–endophyte and plant cell wall–rhizobia interfaces and how metabolite exchange is regulated at these interfaces. While it is easy to postulate that non-structural carbohydrates and other nutrients are transported from plant to microbe, the molecules secreted by endophytes and rhizobia to help plants resist pest or pathogen attack or adapt to drought remain poorly understood. Unravelling the regulation that keeps the cell wall “open” at these interfaces, or identifying the molecules secreted by these beneficial microbes, could enable their synthesis and improve plant defence and growth under stress.In contrast, pathogenic fungi, bacteria and oomycetes secrete CAZymes (polygalacturonases, cellulases) to degrade plant cell walls for invasion and nutrition. Plants detect these CAZymes via pattern recognition receptors, triggering callose deposition, lignification and CAZyme-inhibiting proteins (PGIPs). Pathogens also deliver effectors that suppress wall remodelling, such as blocking ROS-driven lignification or callose synthesis. The balance between pathogen CAZyme activity and plant defences determines disease outcome and offers targets for engineering wall integrity or synthesising protective molecules.This Research Topic welcomes articles focusing, but not limited to, the following themes:-Novel functions of soluble sugars (e.g., trehalose, galactose and complex oligosaccharides) and CAZymes in plant growth and development.-Cell wall modifications during plant growth and development under optimum or stressed conditions.-Cell wall modifications during biotic or abiotic stress, focusing on cell wall remodelling, papilla biochemistry and lignification.-Physiological protective functions of non-structural sugars and metabolic reprogramming during biotic or abiotic stress.-Physiological and ecological functions of structural carbohydrates and CAZymes during plant–beneficial microbe interactions, including molecules secreted by endophytes and rhizobia that prime defence, maintain an “open” cell wall interface, and regulate the symbiosis–defence trade-off.-Microbe-derived CAZymes secreted by endophytes and rhizobia that benefit plants in surviving or adapting to abiotic or biotic stress. Topic editors: Mpho Mafa, Norman Muzhinji, Itumeleng Moroenyane, Steven Hussey Source: https://www.frontiersin.org/research-topics/80131/integrated-roles-of-carbohydrates-and-cazymes-in-plant-health-stress-resilience-and-microbial-interactions