Function of AZI1 in Arabidopsis resistance to Pseudomonas syringae was analyzed using overexpressing,T-DNA knockout and wild-type lines.(1)The expression of AZI1 could be induced by P.syringae,H₂O₂ and ethephon,indicating AZI1 is involved in salicylic acid- and ethylene-mediated antimicrobial pathways.(2)Western blotting analyses showed that AZI1 and its paralog EARLI1 existed in petiole exudate.They could form complexes with other proteins.It suggested that AZI1 possibly moved to other sites of plants through vascular tissue and related with signal transduction.(3)AZI1 and its paralog EARLI1 mainly expressed in lignified tissues of inflorescence stems,overexpression of AZI1 could promote biosynthesis of lignin and enhance the resistance of Arabidopsis to P.syringae.AZI1 belongs to lipid transfer protein (LTP) family.It may play important functions in transduction of signal molecules during defense response of Arabidopsis to infection of P.syringae.