Characterisation of recombinant Hevea brasiliensis allene oxide synthase: effects of cycloxygenase inhibitors, lipoxygenase inhibitors and salicylates on enzyme activity.
Mechanical wounding and jasmonic acid (JA) treatment have been shown to be important factors in controlling laticifer differentiation in Hevea brasiliensis (rubber tree). With the long-term aim of potentially modifying the endogenous levels of JA in H. brasiliensis by gene transfer, we describe in this paper the molecular cloning of a H. brasiliensis allene oxide synthase (AOS) cDNA and biochemical characterisation of the recombinant AOS (His(6)-HbAOS) enzyme. The AOS cDNA encodes a protein with the expected motifs present in CYP74A sub-group of the cytochrome P450 super-family of enzymes that metabolise 13-hydroperoxylinolenic acid (13-HPOT), the intermediate involved in JA synthesis. The recombinant H. brasiliensis AOS enzyme was estimated to have a high binding affinity for 13-HPOT with a K(m) value of 4.02+/-0.64 microM. Consistent with previous studies, mammalian cycloxygenase (COX) and lipoxygenase (LOX) inhibitors were shown to significantly reduce His(6)-HbAOS enzyme activity. Although JA had no effect on His(6)-HbAOS, salicylic acid (SA) was shown to significantly inhibit the recombinant AOS enzyme activity in a dose dependent manner. Moreover, it was demonstrated that SA, and various analogues of SA, acted as competitive inhibitors of His(6)-HbAOS when 13-HPOT was used as substrate. We speculate that this effect of salicylates on AOS activity may be important in cross-talking between the SA and JA signalling pathways in plants during biotic/abiotic stress.
Norton
Gareth
G
Division of Biochemistry and Microbiology, School of Life Sciences, University of Hertfordshire, Hatfield, Herts AL10 9AB, UK.
Pappusamy
Arokiaraj
A
Yusof
Faridah
F
Pujade-Renaud
Valérie
V
Perkins
Mark
M
Griffiths
David
D
Jones
Heddwyn
H
D000595:Amino Acid Sequence; D016861:Cyclooxygenase Inhibitors / Q000737:chemistry*; D003517:Cyclopentanes / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism; D028482:Hevea / Q000378:metabolism*; D019746:Intramolecular Oxidoreductases / Q000737:chemistry*; D007700:Kinetics; D008084:Lipoxygenase / Q000378:metabolism*; D008969:Molecular Sequence Data; D054883:Oxylipins; D010802:Phylogeny; D011994:Recombinant Proteins / Q000737:chemistry; D012459:Salicylates / Q000378:metabolism*; D015398:Signal Transduction; D017962:alpha-Linolenic Acid / Q000737:chemistry
D016861:Cyclooxygenase Inhibitors; D003517:Cyclopentanes; D054883:Oxylipins; D011994:Recombinant Proteins; D012459:Salicylates; D017962:alpha-Linolenic Acid; C011006:jasmonic acid; D003577:Cytochrome P-450 Enzyme System; D008084:Lipoxygenase; D019746:Intramolecular Oxidoreductases; C021377:hydroperoxide isomerase