ORGANIZATION OF THE TOMATO POLYPHENOL OXIDASE GENE FAMILY

We report the isolation and characterization of seven nuclear genes en coding polyphenol oxidase (PPO) in tomato (Lycopersicon esculentum cv. VFNT Cherry). The seven genes (PPOs A, A', B, C, D, E and F) fall int o three structural classes (I, II, and III) based on Eco RI and Hind I II restriction fragment length polymorphisms (RFLP). RFLP mapping and PFGE analysis demonstrated that the genes reside on chromosome 8, and may be clustered within a 165 kb region. Phage insert mapping demonstr ated PPO E and PPO F (both class III), and PPOs B, D and A (classes I, II and I respectively) are grouped within separate 12.4 kb clusters. The complete nucleotide sequence was determined for each gene. Compari son to cDNAs revealed that the PPOs lack introns. A transcript of abou t 2 kb is expected for each PPO. Each PPO possesses a region encoding a transit peptide characteristic of polypeptides targeted to the thyla koid lumen. Predicted precursor polypeptides range in mass from 66 to 71 kDa and predicted mature polypeptides range from 57 to 62 kDa. All the PPOs encode two putative copper-binding sites characteristic of ba cterial, fungal and mammalian tyrosinases. Five of the seven PPOs poss ess divergent DNA sequences in their 5' promoter regions. These flanki ng sequence differences may regulate the differential expression of PP O genes.