Abstract
BackgroundGlucosinolates, a group of nitrogen and sulfur containing compounds associated with plant-insect interactions, are produced by a number of important Brassicaceae crop species. In Arabidopsis the AOP2 gene plays a role in the secondary modification of aliphatic (methionine-derived) glucosinolates, namely the conversion of methylsulfinylalkyl glucosinolates to form alkenyl glucosinolates, and also influences aliphatic glucosinolate accumulation.ResultsThis study characterises the primary structural variation in the coding sequences of the AOP2 gene and identifies three different AOP2 alleles based on polymorphisms in exon two. To help determine the regulatory mechanisms mediating AOP2 expression amongst accessions, AOP2 5' regulatory regions were also examined however no major differences were identified. Expression of the AOP2 gene was found to be most abundant in leaf and stem tissue and was also found to be light dependent, with a number of light regulatory elements identified in the promoter region of the gene. In addition, a study was undertaken to demonstrate that the Arabidopsis AOP2 gene product is functional in planta. The over-expression of a functional AOP2 allele was found to successfully convert the precursor methylsulfinyl alkyl glucosinolate into the alkenyl form.ConclusionsThe expression of the AOP2 gene has been found to be influenced by light and is most highly expressed in the photosynthetic parts of the Arabidopsis plant. The level of AOP2 transcript decreases rapidly in the absence of light. AOP2 exists as at least three alleles in different Arabidopsis accessions and we have demonstrated that one of these, AOP2-2, is functionally able to convert methylsulfinyl glucosinolates into the alkenyl form. The demonstration of the in planta functionality of the Arabisopsis AOP2 gene is an important step in determining the feasibility of engineering glucosinolate profiles in food plants.
Highlights
Glucosinolates, a group of nitrogen and sulfur containing compounds associated with plant-insect interactions, are produced by a number of important Brassicaceae crop species
Analysis of the AOP2 structural gene The AOP2 structural gene was sequenced in Col and the two AOP2-expressing accessions (Cvi and Pi) and two AOP3-expressing accessions (Ler and St)
Much of the genetic and phenotypic diversity evident in natural Arabidopsis accessions occurs as a result of drastic mutations, such as deletions and nucleotide changes resulting in the introduction of stop codons
Summary
Glucosinolates, a group of nitrogen and sulfur containing compounds associated with plant-insect interactions, are produced by a number of important Brassicaceae crop species. Glucosinolates are hydrolysed by myrosinases to produce compounds with a range of biological activities. These activities include the protection of the plant against pathogens and herbivores as well as plant recognition by specialist predators. During the second stage the modified precursor amino acids are converted into glucosinolates (glucone formation), and secondary modification of the glucosinolate structure takes place [1,2,5,6]. Modifications of the basic glucosinolate molecule create an enormous variety of glucosinolate structures. Secondary modification such as oxidation, hydroxylation, methoxylation, desaturation and glycosylation primarily occurs on the methionine side chain and occasionally on the glucose moiety [3]. The side chain modification of the glucosinolate molecule is of particular importance as the structure of the side chain largely determines the nature of the products formed following glucosinolate hydrolysis by myrosinases [3,6]
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