Cloning and expression of a tomato cDNA encoding a methyl jasmonate cleaving esterase

Jasmonic acid and its methyl ester are ubiquitous plant signalling compounds necessary for the regulation of growth and development, as well as for the response of plants to environmental stress factors. To date, it is not clear whether methyl jasmonate itself acts as a signal or if its conversion to jasmonic acid is mandatory prior to the induction of a defense response. We have cloned a cDNA, encoding a methyl jasmonate-cleaving enzyme, from tomato cell suspension cultures. Sequence analysis revealed significant similarity to plant esterases and to (S)-hydroxynitrile lyases with an alpha/beta-hydrolase fold structure. The coding sequence was heterologously expressed in Escherichia coli and purified in a catalytically active form. Transcript levels, as well as enzymatic activity, were determined in different tomato tissues. High transcript levels and enzyme activities were found in roots and flowers, while the mRNA level and activity were low in stems and leaves. Moreover, when tested in methyl jasmonate- and elicitor-treated cell suspension cultures, transcript levels were found to decrease, indicating that this particular enzyme might be a regulator of jasmonate signalling.