Abstract
The fou8 loss of function allele of adenosine bisphosphate phosphatase FIERY1 results in numerous phenotypes including the increased enzymatic oxygenation of fatty acids and increased jasmonate synthesis. Here we show that the mutation causes also profound alterations of sulfur metabolism. The fou8 mutants possess lower levels of sulfated secondary compounds, glucosinolates, and accumulate the desulfo-precursors similar to previously described mutants in adenosine 5′phosphosulfate kinase. Transcript levels of genes involved in sulfate assimilation differ in fou8 compared to wild type Col-0 plants and are similar to plants subjected to sulfate deficiency. Indeed, independent microarray analyses of various alleles of mutants in FIERY1 showed similar patterns of gene expression as in sulfate deficient plants. This was not caused by alterations in signalling, as the fou8 mutants contained significantly lower levels of sulfate and glutathione and, consequently, of total elemental sulfur. Analysis of mutants with altered levels of sulfate and glutathione confirmed the correlation of sulfate deficiency-like gene expression pattern with low internal sulfate but not low glutathione. The changes in sulfur metabolism in fou8 correlated with massive increases in 3′-phosphoadenosine 5′-phosphate levels. The analysis of fou8 thus revealed that sulfate starvation response is triggered by a decrease in internal sulfate as opposed to external sulfate availability and that the presence of desulfo-glucosinolates does not induce the glucosinolate synthesis network. However, as well as resolving these important questions on the regulation of sulfate assimilation in plants, fou8 has also opened an array of new questions on the links between jasmonate synthesis and sulfur metabolism.
Highlights
Arabidopsis gene At5g63980, FIERY1, encodes a bifunctional enzyme possessing 39 (29),59-bisphosphate nucleotidase and inositol polyphosphate 1-phosphatase activities [1]
As the substrate for the enzyme, PAP, is produced during synthesis of glucosinolates (Figure 1), and the gene is coexpressed with genes involved in glucosinolate synthesis [20], we tested whether disruption of FIERY1 affects glucosinolate levels
We revealed the association of FIERY1 with glucosinolate metabolism (Figure 1 and 2) [20] and showed that, as expected, the glucosinolate levels are lower in this mutant than in wild type
Summary
Arabidopsis gene At5g63980, FIERY1, encodes a bifunctional enzyme possessing 39 (29),59-bisphosphate nucleotidase and inositol polyphosphate 1-phosphatase activities [1]. It is similar to yeast Met essential for sulfate assimilation in yeast [5], which catalyses the dephosphorylation of PAPS and PAP. This gene is a target for salt toxicity in yeast and is named alternatively as HAL2 [5]. The genetic screen that gave the Arabidopsis gene the commonly used name FIERY1 or FRY1 was designed to identify genes affecting abscisic acid and stress signalling [2]. Afterwards, the gene has been identified in screens for genes affecting cold signalling as HOS2 (high expression of osmotically responsive genes) [6], for RNA silencing suppressors [7], for elevated expression of ascorbate peroxidase 2 as ALX8 [8], for genes required for venation patterning as RON1 [9], for mutants with deregulated fatty acid oxygenation rate as FOU8 [10], and for mutations affecting expression of phosphate transporter [11]
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