12 - Microbial secondary metabolites and their role in stress management of plants

Abstract

Biotic and abiotic stresses are the principal limiting factors for crop productivity. Biotic stresses in plants are mainly caused by the attack of various pathogens such as fungi, bacteria, oomycetes, virus, viroids, mollicutes, nematodes, herbivores, etc. Whereas, abiotic stresses include salinity, low and high moisture stresses, extremes in temperature, heavy metals toxicity, etc. Microbial secondary metabolites play a vital role in the adaptation of plants to the environment threatened with both biotic and abiotic stress conditions. The ecological significance of the combined action of diverse microorganisms and their different metabolites at the cellular and molecular level on plant growth have been elaborated here. The abundance and diversity of secondary metabolites secretion depend on which biosynthetic genes are present in the genome and on the conditions that induce their expression in response to simple intrinsic or external factors. Several antibiotics produced by protect the plant from different biotic stress, that is, naturally happening continuously. Degradation of the ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC) by bacterial ACC deaminase minimises plant stress and rescues normal plant growth under drought and salt stresses. Induction of diverse osmolytes in microbial colonised plant under abiotic stress condition helps the plant in scavenging the reactive oxygen species generated by stress. Similarly, siderophore, a low-molecular-weight iron-chelating compound in microbes helps in reduction of population of pathogenic microorganism in soil through iron competition. Exopolysaccharides (EPS) of bacterial origin improve soil aggregate as well as helps in biofilm formation which in turn promote rhizobacteria plant asscoiation and enables the plant to develop tolerance against stress. The multifaceted activity of microbes at multilevel communication with root and shoot systems, promote root branching and nutrient uptake capacity, etc., thereby boosting plant growth and yield under stress. Microbial secondary metabolites-mediated interactions in a plant comprise complex mechanisms within the plant cellular system. Biochemical, molecular, and physiological studies support the indepth knowledge generation about the secondary microbial metabolites mediated stress mitigation phenomenon in plants.