Vitamin K1 accumulation in tobacco plants overexpressing bacterial genes involved in the biosynthesis of salicylic acid

Phylloquinone (Vitamin K1) is an essential component of the photosynthetic electron transfer. As isochorismate is required for the biosynthesis of Vitamin K1, isochorismate synthase (ICS) activity is expected to be present in all green plants. In bacteria salicylic acid (SA) is synthesized via a two step pathway involving ICS and isochorismate pyruvate lyase (IPL). The effect of the introduction in tobacco plants of the bacterial ICS and IPL genes on the endogenous isochorismate pathway was investigated. Transgenic tobacco plants in which IPL was targeted to the chloroplast suffered severe growth retardation and had low Vitamin K1 content. Probably because isochorismate was channeled towards SA production, the plants were no longer able to produce normal levels of Vitamin K1. Transgenic tobacco plants in which the bacterial ICS was present in the chloroplast showed higher Vitamin K1 contents than wild type plants.