Chloroplastic Phosphoadenosine Phosphosulfate Metabolism Regulates Basal Levels of the Prohormone Jasmonic Acid in Arabidopsis Leaves

Víctor M Rodríguez,Edward E Farmer,Paul Majcherczyk,Aurore Chételat

doi:10.1104/pp.109.150474

Abstract

Levels of the enzymes that produce wound response mediators have to be controlled tightly in unwounded tissues. The Arabidopsis (Arabidopsis thaliana) fatty acid oxygenation up-regulated8 (fou8) mutant catalyzes high rates of alpha -linolenic acid oxygenation and has higher than wild-type levels of the alpha -linolenic acid-derived wound response mediator jasmonic acid (JA) in undamaged leaves. fou8 produces a null allele in the gene SAL1 (also known as FIERY1 or FRY1). Overexpression of the wild-type gene product had the opposite effect of the null allele, suggesting a regulatory role of SAL1 acting in JA synthesis. The biochemical phenotypes in fou8 were complemented when the yeast (Saccharomyces cerevisiae) sulfur metabolism 3'(2'), 5'-bisphosphate nucleotidase MET22 was targeted to chloroplasts in fou8. The data are consistent with a role of SAL1 in the chloroplast-localized dephosphorylation of 3'-phospho-5'-adenosine phosphosulfate to 5'-adenosine phosphosulfate or in a closely related reaction (e.g. 3',5'-bisphosphate dephosphorylation). Furthermore, the fou8 phenotype was genetically suppressed in a triple mutant (fou8 apk1 apk2) affecting chloroplastic 3'-phospho-5'-adenosine phosphosulfate synthesis. These results show that a nucleotide component of the sulfur futile cycle regulates early steps of JA production and basal JA levels.

Highlights

Levels of the enzymes that produce wound response mediators have to be controlled tightly in unwounded tissues
Induced to a high level in these plants was the transcript of VEGETATIVE STORAGE PROTEIN2 (VSP2), which has long been used as a marker for jasmonate responses (e.g. Berger et al, 1995; Reymond et al, 2004)
To identify new mutants affected in the early steps of oxylipin biosynthesis we performed a genetic screen in resting Arabidopsis Columbia-0 (Col-0) leaves

Summary

Introduction

Levels of the enzymes that produce wound response mediators have to be controlled tightly in unwounded tissues. Concerning oxylipin metabolism, fou displays elevated LOX2 transcript levels and increased AOS catalytic activity and both of these enzymes have confirmed roles in JA synthesis in wounded Arabidopsis (Arabidopsis thaliana) leaves (Bell et al, 1995; Park et al, 2002; Glauser et al, 2009) This fits well with the fact that the mutant has increased basal JA levels in resting leaves and is hypersensitive to wounding, producing 7 times more JA than wild-type plants (Bonaventure et al, 2007a). The double mutant apk apk has reduced levels of these compounds and of the JA precursor 12-oxophytodienoic acid Since both kinases were shown by Mugford et al (2009) to be chloroplast localized, the data underscore the potential of plastid S metabolism to influence jasmonate responses

Methods

Results

Conclusion