The Transcript and Metabolite Networks Affected by the Two Clades of Arabidopsis Glucosinolate Biosynthesis Regulators

Abstract

In this study, transcriptomics and metabolomics data were integrated in order to examine the regulation of glucosinolate (GS) biosynthesis in Arabidopsis (Arabidopsis thaliana) and its interface with pathways of primary metabolism. Our genetic material for analyses were transgenic plants overexpressing members of two clades of genes (ALTERED TRYPTOPHAN REGULATION1 [ATR1]-like and MYB28-like) that regulate the aliphatic and indole GS biosynthetic pathways (AGs and IGs, respectively). We show that activity of these regulators is not restricted to the metabolic space surrounding GS biosynthesis but is tightly linked to more distal metabolic networks of primary metabolism. This suggests that with similarity to the regulators we have investigated here, other factors controlling pathways of secondary metabolism might also control core pathways of central metabolism. The relatively broad view of transcripts and metabolites altered in transgenic plants overexpressing the different factors underlined novel links of GS metabolism to additional metabolic pathways, including those of jasmonic acid, folate, benzoic acid, and various phenylpropanoids. It also revealed transcriptional and metabolic hubs in the “distal” network of metabolic pathways supplying precursors to GS biosynthesis and that overexpression of the ATR1-like clade genes has a much broader effect on the metabolism of indolic compounds than described previously. While the reciprocal, negative cross talk between the methionine and tryptophan pathways that generate GSs in Arabidopsis has been suggested previously, we now show that it is not restricted to AGs and IGs but includes additional metabolites, such as the phytoalexin camalexin. Combining the profiling data of transgenic lines with gene expression correlation analysis allowed us to propose a model of how the balance in the metabolic network is maintained by the GS biosynthesis regulators. It appears that ATR1/MYB34 is an important mediator between the gene activities of the two clades. While it is very similar to the ATR1-like clade members in terms of downstream gene targets, its expression is highly correlated with that of the MYB28-like clade members. Finally, we used the unique transgenic plants obtained here to show that AGs are likely more potent deterrents of the whitefly Bemisia tabaci compared with IGs. The influence on insect behavior raises an important question for future investigation of the functional aspect of our initial finding, which pointed to enriched expression of the MYB28-like clade genes in the abaxial domain of the Arabidopsis leaf.