Serine protease (PubMed:19332543, PubMed:19407393, PubMed:19805099, PubMed:27451395, PubMed:27259555). Has preference for Gln in the P1 position and Lys in the P2 position of oligopeptide substrates. Active also with His in the P1 position (PubMed:19332543). Involved in resistance against insects partly by regulating expression of systemic wound response genes and possibly by its post-ingestive activity in the insect gut. Apart from the role in defense, may be involved in regulation of pectin methylesterases (PMEs) activity and pectin methylesterification of the cell wall (PubMed:27259555). Inhibited by 1 mM 4-(2-aminoethyl)-benzenesulfonyl fluoride (AEBSF), a general inhibitor of serine proteinases, but not by the more selective serine protease inhibitors N-alpha-tosyl-L-lysinyl-chloromethylketone (TLCK), N-tosyl-L-phenylalaninyl-chloromethylketone (TPCK), leupeptin, aprotinin or benzamidine (PubMed:19332543). Its proteolytic activity is autoinhibited by the non-covalent binding of the propeptide to the catalytic domain (PubMed:27451395). No effect on activity by the addition of CaCl(2) or calcium chelators (PubMed:19805099). Optimum pH is 7.5-8.0. 60% of the activity is retained at pH 11.0 (PubMed:19332543). No autolysis at pH 4.0-9.0 in the presence of 5 mM EDTA or 5 mM CaCl(2) (PubMed:19805099). Thermostable (PubMed:19332543, PubMed:27451395, PubMed:19805099). Activity is unaffected by heating to 60 degrees Celsius and only partially reduced after incubation at 70 degrees Celsius (PubMed:19332543). Homodimer. Autocatalytic cleavage is required for the secretion of the mature protein. Expressed in flowers, cotyledons and leaves with the highest expression in roots. Expressed during early seedling development in the micropylar endosperm as well as in the developing root. Also expressed in the mature root system, particularly at the junction between primary and lateral roots. Expressed in the shoot vasculature in both external and internal phloem including sieve elements and companion cells, and also in the vascular (xylem and phloem) parenchyma in 3-week old plants. Expressed in response to mechanical wounding and insect herbivory in leaves. Not expressed in uninjured leaves. The mature polypeptide has three domains: The catalytic domain, an interposed protease-associated (PA) domain required for homodimerization and a C-terminal seven-stranded jelly-roll fibronectin (Fn) III-like domain. The propeptide is required as an intramolecular chaperone for zymogen maturation and secretion. Propeptide is internally cleaved at Asn-38 and Asp-52 in a pH-dependent manner leading to the dissociation of the propeptide from the catalytic domain and resulting in the release of the active subtilase. Cleavage occurs at pH 5.7 and to a stronger extent at pH 5.2. RNAi-mediated knockdown results in partial loss of resistance against M.sexta larvae, impaired systemic induction of late wound response genes and in reduced levels of cell wall homogalacturonan (HG) and pectin methylesterification (DM). Has the potential to be used as an additive in laundry and dishwashing detergents, because it is a calcium-free thermostable subtilase alternative. Belongs to the peptidase S8 family.