File:Pictorial representation showing multifaceted interaction of endophytes with host plants - fmicb-09-02732-g001.jpg

English: Pictorial representation showing multifaceted interaction of endophytes with host plants. (1) Fungal endophytes change chemical and physical characteristics of the leaf such as high-cellulose content and lamina density, which provide toughness resulting in reduced herbivory rates, specifically by leaf–cutting ants. (2) Endophytes prime the host plant’s defensive responses against phytopathogens. Early detection of the phytopathogen by cell surface receptor kinases (RK) and subsequent cytoplasmic kinases (CK) mediate intracellular responses and trigger ethylene/jasmonic acid transduction pathway. (3) Abiotic and biotic stress (signals positively induce expression of the stress-responsive genes, preinvasion defense, and enhanced callose deposition. However, ABA affects negatively signals that trigger systemic acquired resistance. The endophyte significantly modulate stress through the downregulation of ABA. Gibberellins synthesized by plants or endophytes hamper the inhibitory effects of DELLA proteins over the plant-growing signals. (4) Reactive oxygen species (ROS), generated by the plant, are neutralized by the production of enzymes such as superoxide dismutases (SOD), catalases (CatA), peroxidases (POD), alkyl hydroperoxide reductases (AhpC), and glutathione-S-transferases (GSTs ) in endophytes. (5) Protein secretion systems (SSs), which deliver effector proteins (EF) into the plant are either absent or present in low abundance in mutualistic endophytic bacteria. Endophytes also encode specific genes for utilizing aspartate/maltose and dipeptides metabolism. (6) Fungal endophytes modulate the plant’s immune system by the production of chitin deacetylases, which deacetylate chitosan oligomers and, hence, prevent themselves from being recognized by chitin-specific receptors (PR-3) of the plants that recognize chitin oligomers. Perception of flagellin (FLS 2) from endophytes also differs from phytopathogens. (7) Endophytic microbes alleviate metal phytotoxicity via extracellular precipitation, intracellular accumulation, sequestration, or biotransformation of toxic metal ions to less toxic or non-toxic forms. Where, RK, receptor kinase; CK, cytoplasmic kinase; ET, ethylene; JA, jasmonic acid; SK, sensor kinase; GA, gibberellic acid; DELLA, DELLA protein; ABA, abscisic acid; SA, salicylic acid; HSP, heat shock protein; ROS, reactive oxygen species; SOD, superoxide dismutases; CatA, catalases; POD, peroxidases; AhpC, alkyl hydroperoxide reductases; GSTs, glutathione-s-transferases; EF, effector protein; PR-3, chitin-specific receptors; FLS 2, flagellin; TTSS, type III secretion system; SS, secretion system; MT, metal transporters; IC, ion channels; CW, bacterial cell wall.)