Molecular characterization of the polyphenol oxidase gene in lulo (Solanum quitoense Lam.) var. Castilla

Lulo (Solanum quitoense Lam.) is an exotic fruit from the Andes Mountains with a high export potential. However, the browning that is produced during harvest and the postharvest processes alters the organoleptic and nutritional properties of this fruit, which has made its management as a fresh fruit difficult. The browning processes are regulated by the enzyme family of the polyphenol oxidases (PPOs) located in the thylakoids of the chloroplast. When there is damage at the tissue level, the phenolic compounds found in the vacuoles enter into contact with the polyphenol oxidase. This enzyme produces polymerization among the phenolic compounds, as well as between them and the proteins and cell walls. This study analyzed the polyphenol oxidase in lulo var. Castilla at the genetic level, based on DNA and RNA samples. The results showed a high level of homology with other polyphenol oxidases from plants. The highest degree of homology was found with Solanum melongena L., which belongs to the same clade, Leptostemonum. The tyrosinase and two copper-binding domains, characteristic of the polyphenol oxidase, the conserved residues that maintain the natural environment, the sequence of a signal peptide for targeting chloroplast, and the UTRA domain of transcription regulation for recognizing small molecules were identified. Southern blot was used to analyze the number of gene copies, identifying at least eight ones in the lulo genome.