Differential Expression of Genes Involved in the Biosynthesis and Perception of Ethylene during Ripening of Passion Fruit (Passiflora edulis Sims)

An increase in the enzyme activity of 1-aminocyclopropane-1-carboxylicacid (ACC) synthase and ACC oxidase induces the evolution ofethylene during the ripening of passion fruit. A much higherlevel of ethylene is produced in arils than in seeds or peelsduring ripening. The pattern of expression of two ACC synthasegenes (PE-ACS1 and PE-ACS2), one ACC oxidase gene (PE-ACO1),and two ethylene receptor genes (PE-ETR1 and PE-ERS1) revealedthat the expression of these genes is differentially regulated.Expression of PE-ACS1 and PE-ACO1 was enhanced during ripeningand after ethylene treatment. However, prominent expressionof PE-ACS1 was delayed compared to that of PE-ACO1. Much largerquantities of PE-ACS1 mRNA and PE-ACO1 mRNA were seen in arilsthan in seeds; this corresponds well with an increase in theamount of ethylene produced by the plant tissue itself. Thelevel of PE-ACS2 mRNA was detectable in arils of the preclimactericfruit, although it decreased during ripening. These resultssuggest that expression of PE-ACS1 and PE-ACO1 is required toincrease the activity of ethylene biosynthetic enzymes duringripening. The level of expression of PE-ETR1 and PE-ERS1 didnot significantly change over the course of ripening; however,the mRNA levels of PE-ETR1 and PE-ERS1 were much higher in arilsthan in seeds. ⁴Present address: Center forMolecular Genetics Research, Shizuoka University, Shizuoka, 422-8529 Japan.