OLIVE - A KEY GENE REQUIRED FOR CHLOROPHYLL BIOSYNTHESIS IN ANTIRRHINUM-MAJUS

Olive (oli) is a recessive nuclear mutation of Antirrhinum majus which reduces the level of chlorophyll pigmentation and affects the ultrast ructure of chloroplasts. The oli-605 allele carries a Tam3 transposon insertion which has allowed the locus to be isolated. The oli gene enc odes a large putative protein of 153 kDa which shows homology to the p roducts of two bacterial genes necessary for tetrapyrrole-metal chelat ion during the synthesis of bacteriochlorophyll or cobyrinic acid. We therefore propose that the product of the oli gene is necessary for a key step of chlorophyll synthesis: the chelation of magnesium by proto porphyrin IX. Somatic reversion of the oli-605 allele produces chimeri c plants which indicate that the oli gene functions cell-autonomously. Expression of oli is restricted to photosynthetic celts and repressed by light, suggesting that it may be involved in regulating the rate o f chlorophyll synthesis in green tissues.