Probable lipase required downstream of MPK4 for accumulation of the plant defense-potentiating molecule, salicylic acid, thus contributing to the plant innate immunity against invasive biotrophic pathogens and to defense mechanisms upon recognition of microbe-associated molecular patterns (MAMPs). Participates in the regulation of various molecular and physiological processes that influence fitness. Together with SG101, required for programmed cell death (PCD) triggered by NBS-LRR resistance proteins (e.g. RPS4, RPW8.1 and RPW8.2) in response to the fungal toxin fumonisin B1 (FB1) and avirulent pathogens (e.g. P.syringae pv. tomato strain DC3000 avrRps4 and pv. maculicola, turnip crinkle virus (TCV), and H.arabidopsidis isolates CALA2, EMOY2, EMWA1 and HIND4). Together with EDS1, confers a basal resistance by restricting the growth of virulent pathogens (e.g. H.arabidopsidis isolates NOCO2 and EMCO5, E.orontii isolate MGH, and P.syringae pv. tomato strain DC3000 or expressing HopW1-1 (HopPmaA)). Necessary for the salicylic acid-(SA-) dependent systemic acquired resistance (SAR) response that involves expression of multiple defense responses, including synthesis of the phytoalexin camalexin and expression of pathogenesis-related genes (e.g. PR1, ALD1, BGL2 and PR5) in response to pathogens, triggering a signal amplification loop that increases SA levels via EDS5 and SID2, but, together with EDS1, seems to repress the ethylene/jasmonic acid (ET/JA) defense pathway. May also function in response to abiotic stresses such as UV-C light and LSD1-dependent acclimatization to light conditions that promote excess excitation energy (EEE), probably by transducing redox signals and modulating stomatal conductance. Regulates the formation of lysigenous aerenchyma in hypocotyls in response to hypoxia, maybe via hydrogen peroxide production. Modulates leaf senescence in insect-infested tissue and triggers a phloem-based defense mechanism including antibiosis (e.g. green peach aphid (GPA), M.persicae) to limit phloem sap uptake and insect growth, thus providing an EDS1-independent basal resistance to insects. Also involved in regulation of root meristematic zone-targeted growth arrest together with EDS1 and in a VICTR-dependent manner.
