Integrated ‘Omics’ Analysis of TGG1 and TGG2 Function

The glucosinolate-myrosinase system in plants of the order Capparales including cruciferous crops and the model plant Arabidopsis thaliana serves as a chemical defence mechanism against bacteria, fungi and insects (Bones and Rossiter 1996). Upon tissue damage, the enzyme myrosinase (β-thioglucoside glucohydrolase, TGG) degrades glucosinolates to bioactive compounds. In Arabidopsis, the myrosinase gene family consists of four functional genes (Xu et al. 2004). To elucidate the function of TGG1 and TGG2, gene expression-, protein- and metabolite profiling was performed on T-DNA knockout mutants (respectively TGG1KO and TGG2KO) grown on soil. Microarray data showed no statistically significant change in the GLS biosynthesis pathway when comparing the knockouts with wt. This is consistent with the metabolite data where no significant difference in GLS or their degradation product profile could be detected. When TGG2 is knocked out, the lost myrosinase activity is apparently compensated by induced expression of TGG1. In the case of TGG1 knockout, almost all myrosinase activity was eliminated without affecting the expression of TGG2. TGG1 and TGG2 have been shown to have redundant function in insect defence (Barth and Jander 2006). Our study on pathogen infection showed that TGG1 and TGG2 might have different function. Upon Botrytis cinerea infection, TGG1KO and TGG2KO showed different expression patterns. No increased susceptibility to Pseudomonas syringae was observed in TGG1KO and TGG2KO. Additional information is provided by protein profiling data. REFERENCES: Bones, A.M. and Rossiter, J.T. (1996). The myrosinase–glucosinolate system, its organisation and biochemistry. Physiol. Plant. 97, 194–208. Xu, Z., Escamilla-Trevino, L., Zeng, L. et al. (2004).Functional genomic analysis of Arabidopsis thaliana glycoside hydrolase family 1. Plant Mol. Biol. 55, 343–367. Barth, Carina & Jander, Georg (2006).Arabidopsis myrosinases TGG1 and TGG2 have redundant function in glucosinolate breakdown and insect defense. The Plant Journal 46 (4), 549-562.