A tomato enzyme synthesizes (+)-7-iso-jasmonoyl-l-isoleucine in wounded leaves
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Jasmonoyl-l-isoleucine (JA-Ile) is a key jasmonate signal that probably functions in all plant species. The JASMONATE RESISTANT 1 (JAR1) enzyme synthesizes JA-Ile in Arabidopsis [Arabidopsis thaliana (L.) Heynh.], but a similar enzyme from tomato [Solanum lycopersicum (L.)] was not previously described. Tomato SlJAR1 has 66% sequence identity with Arabidopsis JAR1 and the SlJAR1-GST fusion protein purified from Escherichia coli catalyzed the formation of JA-amino acid conjugates in vitro. Kinetic analysis showed the enzyme has a strong preference for Ile over Leu and Val and it was about 10-fold more active with (+)-7-iso-JA than with its epimer (−)-JA. Leaf wounding rapidly increased JA-Ile 50-fold to about 450 pmol g−1 FW at 30 min after wounding, while conjugates with Leu, Phe, Val and Met were only marginally increased or not detected. Nearly all of the endogenous JA-Ile was the bioactive epimer (+)-7-iso-JA-Ile and there was no evidence for its conversion to (−)-JA-Ile up to 6 h after wounding. A transgenic RNAi approach was used to suppress SlJAR1 transcript that reduced JA-Ile accumulation by 50–75%, suggesting that other JA conjugating enzymes may be present. These results show that SlJAR1 synthesizes the bioactive conjugate (+)-7-iso-JA-Ile and this is the predominant isomer accumulated in wounded tomato leaves.
KeywordsJAR1 Jasmonic acid Jasmonoyl-l-isoleucine Tomato Wounding
Gas chromatography/mass spectrometry
Glutathione S transferase
Jasmonate ZIM domain
Polymerase chain reaction
The authors thank G. Howe for providing the jai1 mutant and for helpful discussions. We also acknowledge the expertise of T. Clemente and the University of Nebraska Transformation Facility for providing the tomato transformants. This research is a contribution of the University of Nebraska Agricultural Research Division, supported in part by funds from the Hatch Act. Additional support was provided by the National Science Foundation (Awards MCB-0130868, IOS-0744758).
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