ABSTRACT
Plants, being sessile organisms, have to encounter numerous pathogens in their environment, which they counter through a robust defence system that comprises two different recognition systems that initiate pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). At the same time, plants have to live in harmony with various symbiotic and mutualistic organisms, including phosphate-solubilising microorganisms (PSMs), which plants depend on for various nutrients and their overall fitness. Phosphorus is one of the most essential macronutrients required by plants, and, consequently, it is impossible for plants to grow without a dependable supply of this nutrient. Hence, plants have evolved complex phosphate-starvation responses (PSRs) that regulate morphological and physiological adaptive changes when phosphorus availability is limited. In addition, depending on the phosphorus status in the soil, plants have the ability to fine-tune the microbiota associated with them for their benefit. Furthermore, a high degree of cross-talk on defence hormones and phosphorus availability is in place, which regulates the plant defence responses. Phosphorylation also plays a predominant role in signal transduction after pathogen perception. Microbe-associated molecular pattern (MAMP) perception by pattern-recognition receptors (PRRs) and pathogen effector recognition by R gene products, such as nucleotide-binding leucine-rich repeat proteins (NB-LRRs), lead to ligand-receptor complex formation and results in different auto- and trans-phosphorylation reactions of the different players, consequently activating the mitogen-activated protein kinase (MAPKs) cascades that regulate an array of downstream defence responses by phosphorylation of target proteins, including transcription factors and enzymes.
