Arabidopsis thaliana contain three different patterns of 2-hydroxybut-3-enyl GSL accumulation (present in leaves and seeds; seeds only; or absent) corresponding to three different alleles at a single locus GSL-OH. Fine-scale mapping of the GSL-OH locus identified a 2-oxoacid-dependent dioxygenase encoded by At2g25450 required for the formation of both 2R- and 2S-2-hydroxybut-3-enyl GSL from the precursor 3-butenyl GSL precursor. Naturally occurring null mutations and T-DNA insertional mutations in At2g25450 exhibit a complete absence of 2-hydroxybut-3-enyl GSL accumulation. Analysis of herbivory by the generalist lepidopteran Trichoplusia ni showed that production of 2-hydroxybut-3-enyl GSL provides increased resistance. These results show that At2g25450 is necessary for the hydroxylation of but-3-enyl GSL to 2-hydroxybut-3-enyl GSL in planta and that this metabolite increases resistance to generalist herbivory (Hansen et al. 2008)