tomato enzyme synthesizes (+)-7-iso-jasmonoyl-l-isoleucine in wounded leaves

• Published in: Planta 2010-02, Vol.231 (3), p.717-728
• Main Authors: Suza, Walter P, Rowe, Martha L, Hamberg, Mats, Staswick, Paul E
• Format: Article
• Language: English
• Subjects: Agriculture; Amino acids; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - physiology; Biological and medical sciences; Biomedical and Life Sciences; Cyclopentanes; E coli; Ecology; Enzymes; Flowers; Forestry; Fundamental and applied biological sciences. Psychology; Isoleucine - analogs & derivatives; Isoleucine - biosynthesis; Isomers; Kinetics; Leaves; Life Sciences; Lycopersicon esculentum - enzymology; Lycopersicon esculentum - metabolism; Nucleotidyltransferases - chemistry; Nucleotidyltransferases - physiology; Original Article; Plant cells; Plant Leaves - enzymology; Plant Leaves - metabolism; Plant Proteins - chemistry; Plant Proteins - physiology; Plant roots; Plant Sciences; Plant species; Plants; Plants, Genetically Modified - metabolism; RNA; RNA Interference; RNA, Messenger - metabolism; Signal Transduction; Substrate Specificity; Tomatoes
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-009-1080-6

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.