Four uncharacterized FMOs designated FMOGS-OX2 to FMOGS-OX5 were found to involve in biosynthesis aliphatic GSL. Biochemical characterization of the recombinant protein combined with the analysis of GSL content in knockout mutants and overexpression lines show that FMOGS-OX2; FMOGS-OX3; and FMOGS-OX4 have broad substrate specificity and catalyze the conversion from methylthioalkyl GSL to the corresponding methylsulfinylalkyl GSL independent of chain length. In contrast; FMOGS-OX5 shows substrate specificity toward the long-chain 8-methylthiooctyl GSL. Identification of the FMOGS-OX subclade will generate better understanding of the evolution of biosynthetic activities and specificities in secondary metabolism and provides an important tool for breeding plants with improved cancer prevention characteristics as provided by the methylsulfinylalkyl GSL (Li et al. 2008)