Isochorismate synthase transgenic expression in Catharanthus roseus cell suspensions

Cell suspensions of Catharanthus roseus produce 2,3-dihydroxybenzoic acid (2,3-DHBA) after elicitation with fungal elicitor. Together with the 2,3-DHBA production there is a strong increase in isochorismate synthase (ICS; EC 5.4.99.6) activity, an enzyme which converts chorismate into isochorismate. Bacteria also produce 2,3-DHBA which is an intermediate for the biosynthesis of siderophores. The biosynthesis pathway of 2,3-DHBA in bacteria proceeds via ICS. To investigate whether C. roseus cells use the same pathway to produce 2,3-DHBA, cells were transformed with constructs containing a C. roseus cDNA clone of ics in sense or antisense orientation. Although the transformation with ics in sense orientation resulted in constitutive ICS activity, no accumulation of 2,3-DHBA was observed. Transformation of ics in antisense orientation was not sufficient to block the ICS production. The biosynthesis of 2,3-DHBA in C. roseus probably involves a multi-enzyme pathway, which cannot simply be modulated by over-expression of ics.