Ethylene-driven expression of genes involved in carotenoid biosynthesis during postharvest ripening is different in creole and commercial Carica papaya L. fruits

This paper reports ethylene production, expression levels of ethylene precursor’s genes, as well as carotenoid content and expression levels of carotenoid biosynthesis genes, during postharvest ripening of three different papaya genotypes of contrasting origin (2 creoles and 1 commercial) and pulp color (yellow, orange and red), under conditions that promote ethylene formation and under those inhibiting ethylene. Our study showed that naturally ripened papaya fruits presented relatively high ethylene production levels that was correlated with changes in expression levels of both ethylene precursor’s genes (CpACCs1, CpACCs2, CpACCo1 and CpACCo2), and carotenoid biosynthesis genes (CpPSY, CpZDS, CpLCY-β2, CpCHX-β). However, when papaya fruits were treated with an ethylene inducer (Ethephon; 2.5 g L^− 1 of 2-chloroethyl-phosphonic acid) fruits ripened faster (two days earlier than controls), and they also showed a higher ethylene peak and higher expression levels of both ethylene precursors genes and carotenoid biosynthesis genes, than control fruits. In contrast, papaya fruits treated with an ethylene inhibitor (1-MCP; 300 nL L^− 1 of 1-methylcyclopropene) never ripened (in fact they did not show changes in fruit firmness, °Brix, pH or acidity), and they showed very low ethylene production and low expression levels of ethylene precursors genes, as well as showing low expression of carotenogenic genes, throughout the postharvest ripening process. Correlation analysis showed that increased ethylene production was highly correlated with increased expression of both ethylene precursors genes and carotenoids biosynthesis genes, but the specific carotenogenic genes induced by ethylene differed among commercial and creole papaya genotypes.