Isochorismate synthase involved in the synthesis of salicylic acid (SA) required for both local and systemic acquired resistance (LAR and SAR) while SA synthesized through the phenylalanine ammonium lyase (PAL) pathway seems to potentiate plant cell death. Also involved in phylloquinone (vitamin K1) synthesis. Has no isochorismate pyruvate lyase (IPL) activity. chorismate = isochorismate Siderophore biosynthesis; salicylate biosynthesis. A number of isoforms are produced. According to EST sequences. No visible phenotype; due to the redundancy with ICS1. Mutants are not impaired in salicylic acid accumulation upon induction. Ics1 and ics2 double mutant is seedling lethal due to photosynthetic lesions induced by the lack of phylloquinone. Belongs to the isochorismate synthase family.