α‐Glucosidase hydrolyzes α‐glucosides and transfers α‐glucosyl residues to an acceptor through transglucosylation. In this study, GH13_31 α‐glucosidase BspAG13_31A with high transglucosylation activity is reported in Bacillus sp. AHU2216 and biochemically and structurally characterized. This enzyme is specific to α‐(1→4)‐glucosidic linkage as substrates and transglucosylation products. Maltose is the most preferred substrate. Crystal structures of BspAG13_31A wild‐type for the substrate‐free form and inactive acid/base mutant E256Q in complexes with maltooligosaccharides were solved at 1.6–2.5 Å resolution. BspAG13_31A has a catalytic domain folded by an (β/α)₈‐barrel. In subsite +1, Ala200 and His203 on β→α loop 4 and Asn258 on β→α loop 5 are involved in the recognition of maltooligosaccharides. Structural basis for specificity of GH13_31 enzymes to α‐(1→4)‐glucosidic linkage is first described.

Salicylic acid (SA) is a phytohormone that regulates a variety of physiological and developmental processes, including disease resistance. SA is a key signaling component in the immune response of many plant species. However, the mechanism underlying SA-mediated immunity is obscure in rice (Oryza sativa). Prior analysis revealed a correlation between basal SA level and blast resistance in a range of rice varieties. This suggested that resistance might be improved by increasing basal SA level. Here, we identified a novel UDP-glucosyltransferase gene, UGT74J1, which is expressed ubiquitously throughout plant development. Mutants of UGT74J1 generated by genome editing accumulated high levels of SA under non-stressed conditions, indicating that UGT74J1 is a key enzyme for SA homeostasis in rice. Microarray analysis revealed that the ugt74j1 mutants constitutively overexpressed a set of pathogenesis-related (PR) genes. An inoculation assay demonstrated that these mutants had increased resistance against rice blast, but they also exhibited stunted growth phenotypes. To our knowledge, this is the first report of a rice mutant displaying SA overaccumulation.