ALLENE OXIDE SYNTHASE and HYDROPEROXIDE LYASE, Two Non-Canonical Cytochrome P450s in Arabidopsis thaliana and Their Different Roles in Plant Defense.

Sachin Rustgi,Diter Von Wettstein,Armin Springer,Chulhee Kang,Stephan Pollmann,Christiane Reinbothe,Steffen Reinbothe

doi:10.3390/ijms20123064

Abstract

The channeling of metabolites is an essential step of metabolic regulation in all living organisms. Multifunctional enzymes with defined domains for metabolite compartmentalization are rare, but in many cases, larger assemblies forming multimeric protein complexes operate in defined metabolic shunts. In Arabidopsis thaliana, a multimeric complex was discovered that contains a 13-lipoxygenase and allene oxide synthase (AOS) as well as allene oxide cyclase. All three plant enzymes are localized in chloroplasts, contributing to the biosynthesis of jasmonic acid (JA). JA and its derivatives act as ubiquitous plant defense regulators in responses to both biotic and abiotic stresses. AOS belongs to the superfamily of cytochrome P450 enzymes and is named CYP74A. Another CYP450 in chloroplasts, hydroperoxide lyase (HPL, CYP74B), competes with AOS for the common substrate. The products of the HPL reaction are green leaf volatiles that are involved in the deterrence of insect pests. Both enzymes represent non-canonical CYP450 family members, as they do not depend on O2 and NADPH-dependent CYP450 reductase activities. AOS and HPL activities are crucial for plants to respond to different biotic foes. In this mini-review, we aim to summarize how plants make use of the LOX2–AOS–AOC2 complex in chloroplasts to boost JA biosynthesis over volatile production and how this situation may change in plant communities during mass ingestion by insect pests.

Highlights

Itnhteeyresptrinegsulym, eaicbolysanaoctidi-nliktehecodmepteorurnednscehaovfembeicenrobial pathoigdeenntsif[i4e–d6i]n. soft corals and other marine organisms where they presumably act in the deterrence of Wmihcarotbaipalppeaatrhsogtoenbse[4p–r6o].staglandins in animals are jasmonates in plants (Figure 1)
Replacing the amino acids involved in these steps by non-polar residues, as encountered in the allene oxide synthase (AOS)(F137L, S155A) mutant derivative, prevents a carbocation intermediate from being adequately enriched or stabilized at C11 and prevented the formation of an unstable hemiacetal [50], which spontaneously dissociates into short-chain aldehydes
Of the two catalase-lipoxygenase fusion protein genes identified in the coral Capnella imbricate, gene A encodes a wound-responsive AOS-type enzyme and gene B encodes an HPL-type enzyme specialized for the synthesis of short-chain aldehydes [78,83]

Summary

Introduction

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Objectives

Results

Conclusion