FIGURE 3.

Schematic representation of the MAMPs, DAMPs, NF, and effectors-mediated activation of the ACC and ET biosynthesis and signaling pathways. MAMPs, DAMPs and NFs bind to their cognate receptors present in the plant cell outer membrane and, consequently, initiate the respective signal transduction pathways that lead to the production of ACC and ET. Since most MAMPs, DAMPs and NFs are known to activate MKK-MPK signaling cascades, a MAMP, DAMP and NF-triggered MKK-MPK3/6 cascade (based on Arabidopsis gene nomenclature) seems to play a central role in the phosphorylation, and, subsequent activation of type 1 ACS (e.g., AtACS2 and AtACS6). Nevertheless, some aspects of the MAMP, DAMP, NF, and effector induced-R protein signal transduction pathways remain elusive. For example, effector induced immunity leads to the production of ACC and ET, however, not much is understood about the role of effectors and R proteins in the activation of the ET biosynthesis and signaling pathways. MAMP, Microbe Associated Molecular Pattern; DAMP, Damage Associated Molecular pattern; FLG, Flagellin; EF-Tu, Elongation factor-Tu; LPS, Lipopolysaccharide; PGN, Peptidoglycan; NLPs, necrosis and ethylene-inducing peptides; NF, Nodulation factors; FLS2, flagellin receptor; EFR, elongation factor-Tu receptor; RLP23, necrosis and ethylene- inducing peptides receptor; LORE, lipopolysaccharide receptor; LYM1 and LYM3, peptidoglycan receptors; NFP and LYK3, nodulation factor receptors; PEPR1-2, Pep1 receptor. R, resistance protein involved in effector recognition; CERK1, LysM receptor kinase; FRK1 -Flg22-Induced Receptor-Like Kinase 1; BAK1, Brassinosteroid insensitive 1 (BRI1)-associated kinase; BIK1, Botrytis-Induced Kinase 1; MKK, mitogen-activated protein kinase kinase; MPK, mitogen-activated protein kinase. ACS, ACC synthase; ACO, ACC oxidase; ERF, Ethylene Response Factor.