Caracterización estructural y filogenética de un gen de polifenol oxidasa en lulo (Solanum quitoense Lam.)

The lulo or naranjilla (Solanum quitoense Lam.) is one of the most important Colombian native fruits. The sale and industrial processing of fresh fruit is severely limited by enzymatic browning. Until now, there was no knowledge about polyphenol oxidases (PPO) in lulo. The aim of this study was to understand some structural and phylogenetic aspects of the first lulo ppo gene that has been characterized. Using two pairs of degenerate primers, two fragments of lulo genomic DNA were isolated by PCR, sequenced and assembled into a partial sequence of 1417 bp (SquPPO1) lacking introns. Hybridization of a 920-bp probe generated from a potato ppo gene with a 12 kb region of BamHI-PstI, BamHI-XbaI and XbaI-PstI digested lulo DNA confirmed the presence of at least one ppo gene in this species. While two conserved sites (Tyr-1 and Tyr-2) have been identified in the copper-binding domains of other Solanaceae PPOs, no Tyr-2 site was found in lulo PPO because of a conservative substitution DxE in this region. Phylogenetic analysis placed the SquPPO1 gene in the same cluster as the SmePPO4, SmePPO5, and SmePPO6 eggplant (Solanum melongena L.) genes. Our results show that SquPPO1 is phylogenetically closer to eggplant ppo genes than to those of potato, tobacco, and tomato and that it exhibits a variation that modifies the distribution of protein-conserved sites. These findings offer new insights into the molecular basis of enzymatic browning in lulo and may inform strategies to reduce postharvest losses.