A novel 2-oxoacid-dependent dioxygenase involved in the formation of the goiterogenic 2-hydroxybut-3-enyl glucosinolate and generalist insect resistance in Arabidopsis,

Modifying the alkylglucosinolate profile in Arabidopsis thaliana alters the tritrophic interaction with the herbivore Brevicoryne brassicae and parasitoid Diaeretiella rapae

Arabidopsis thaliana was used as an experimental model plant to investigate a tritrophic interaction between the plant, a specialist aphid herbivore, Brevicoryne brassicae, and its natural enemy, the parasitoid Diaeretiella rapae. The A. thaliana ecotype Col-5 was transformed with a functional 2-oxoglutarate dependent dioxygenase (BniGSL-ALK) that converts 3-methylsulfinylpropylglucosinolate and 4-methylsulfinylbutylglucosinolate to 2-propenylglucosinolate and 3-butenylglucosinolate, respectively. This transformation results in a change in the glucosinolate hydrolysis profile where 3-butenylisothiocyanate, 2-propenylisothiocyanate and 5-vinyloxazolidine-2-thione are produced in contrast to the wild-type plant where 4-methylsulfinylbutylisothiocyanate is the main product. Performance of B. brassicae was affected negatively by transforming Col-5 with BniGSL-ALK in terms of mean relative growth rates. In a series of behavioral bioassays, naïve D. rapae females were able to discriminate between B. brassicae infested and uninfested Col-5 plants transformed with BniGSL-ALK, with parasitoids showing a preference for B. brassicae infested plants. By contrast, naïve D. rapae females were unable to discriminate between aphid infested and uninfested Col-5 plants. Subsequent air entrainments of B. brassicae infested Col-5 plants transformed with BniGSL-ALK further confirmed the presence of 3-butenylisothiocyanate in the headspace. By contrast, no glucosinolate hydrolysis products were recorded from similarly infested Col-5 plants.

Advancing genetic theory and application by metabolic quantitative trait loci analysis

This review describes recent advances in the analysis of metabolism using quantitative genetics. It focuses on how recent metabolic quantitative trait loci (QTL) studies enhance our understanding of the genetic architecture underlying naturally variable phenotypes and the impact of this fundamental research on agriculture, specifically crop breeding. In particular, the role of whole-genome duplications in generating quantitative genetic variation within a species is highlighted and the potential uses of this phenomenon presented. Additionally, the review describes how new observations from metabolic QTL mapping analyses are helping to shape and expand the concepts of genetic epistasis.

Genome-wide identification of glucosinolate synthesis genes in Brassica rapa

Glucosinolates play important roles in plant defense against herbivores and microbes, as well as in human nutrition. Some glucosinolate-derived isothiocyanate and nitrile compounds have been clinically proven for their anticarcinogenic activity. To better understand glucosinolate biosynthesis in Brassica rapa, we conducted a comparative genomics study with Arabidopsis thaliana and identified total 56 putative biosynthetic and regulator genes. This established a high colinearity in the glucosinolate biosynthesis pathway between Arabidopsis and B. rapa. Glucosinolate genes in B. rapa share 72-94% nucleotide sequence identity with the Arabidopsis orthologs and exist in different copy numbers. The exon/intron split pattern of B. rapa is almost identical to that of Arabidopsis, although inversion, insertion, deletion and intron size variations commonly occur. Four genes appear to be nonfunctional as a result of the presence of a frame shift mutation and retrotransposon insertion. At least 12 paralogs of desulfoglucosinolate sulfotransferase were found in B. rapa, whereas only three were found in Arabidopsis. The expression of those paralogs was not tissue-specific but varied greatly depending on B. rapa tissue types. Expression was also developmentally regulated in some paralogs but not in other paralogs. Most of the regulator genes are present as triple copies. Accordingly, glucosinolate synthesis and regulation in B. rapa appears to be more complex than that of Arabidopsis. With the isolation and further characterization of the endogenous genes, health-beneficial vegetables or desirable animal feed crops could be developed by metabolically engineering the glucosinolate pathway.