Genome-wide identification of jasmonate biosynthetic genes and characterization of their expression profiles during apple (Malus x domestica) fruit maturation

The plant hormones regulate most physiological processes including apple fruit ripening by integrating diverse developmental cues and environmental signals. In addition to the well-characterized role of ethylene, jasmonic acid (JA) and its derivatives have also been suggested to play an important role during apple fruit maturation and ripening. Till now, the role JA on apple fruit ripening was only observed through exogenous application of JA or its derivatives. The de novo JA biosynthesis and signal transduction in apple fruit tissues have not been studied. In this study, the members of major gene families implicated in JA biosynthesis were identified from apple genome sequences; and their expression profiles were characterized in 'Golden Delicious' using quantitative reverse transcription polymerase chain reactions. Our data indicated that the expression patterns of MdLOX23, MdAOS2 and MdJMT2 in JA biosynthesis pathway are coordinated with those of MdACS3, MdERF1 and MdERF2 genes during 12 consecutive weeks of apple fruit maturation toward commercial harvest. Both MdLOX23 and MdAOS2 showed comparable expression patterns in both core and cortex suggesting localized synthesis of JA in different fruit tissues. Most of JA biosynthesis genes were transiently up-regulated in response to exogenous application of methyl jasmonate to on-tree maturing apple fruit, though in a maturity dependent manner. Our results suggested regulating roles of JA biosynthesis and its signaling on apple fruit maturation and ripening.