Effector Mediated Defense Mechanisms in Plants against Phytopathogens

Plants in environment are often exposed to pathogenic attack to which they respond through numerous morphological, biochemical, and molecular mechanisms. Plant parasites while forming association with host delivers proteins and suites of effector molecules needed for infestation. The host system in turn triggers innate immunity through the interactive signaling pathways involving the membrane-bound or intracellular receptors that perceive different elicitors such as pathogen-associated molecular patterns (PAMPs/MAMPs), damage-associated molecular patterns (DAMPs) released by microbial enzymes or effectors, thereby causing a PAMP-triggered immunity (PTI) or an effector-triggered immunity (ETI). PTI results into basal immunity, whereas ETI confers durable immunity that finally results in hypersensitive responses (HR). While hypersensitive responses and systemic acquired resistance (SAR) are triggered in plants on exposure to different compatible pathogens, the induced systemic resistance (ISR) are elicited by plant growth-promoting rhizobacteria (PGPR), categorized as incompatible pathogens. Phytopathogenic bacteria, oomycetes, and fungi inject effectors into host plant body thereby damaging the host metabolism causing infection. These effectors many times trigger resistance in host plant as well. Effectors of non-pathogenic endophytic microbes establish a different response by founding a mutualistic relationship with host plant, positively regulating the plant health. The present review therefore discusses effectoromics undermining plant expressions during infection and host immune responses.