Expression pattern of the glucosinolate side chain biosynthetic genes MAM1 and MAM3 of Arabidopsis thaliana in different organs and developmental stages

Aliphatic glucosinolates, secondary metabolites known to be involved in plant defence, make up the majority of the glucosinolate content of Arabidopsis thaliana, and their structural diversity arises in part from chain elongations of methionine before the formation of the glucosinolate core structure. The key enzymatic step in determining the length of the chain is the condensation of acetyl-coenzyme A with a series of ω-methylthio-2-oxoalkanoic acids, catalyzed by methylthioalkylmalate (MAM) synthases. The existence of two MAM synthases has been previously reported in A. thaliana, ecotype Columbia-0. MAM1 catalyses the condensation step of the first three elongation cycles while MAM3 catalyzes the condensation step of all six elongation cycles. We studied the expression patterns of MAM1 and MAM3 genes in different organs and developmental stages using promoter-GUS fusion lines and qRT-PCR. The promoter-GUS lines revealed MAM1 and MAM3 expression in varying degrees in all organs, but this was generally restricted to the phloem, except in wounded tissue where expression was general. No difference was found between the two genes. The qRT-PCR measurements showed that expression was generally highest in seedlings and vegetative parts at the reproductive phase, but low in flowers and fruits. Since high amounts of glucosinolates accumulate in flowers and fruits, these data indicate possible transport from vegetative to reproductive organs. The expression of MAM1 was different than that of MAM3 with MAM3 having relative more expression in seedlings and roots than MAM1.