engleski

Localization of Aaliphatic Glucosinolate Biosynthesis and their Potential Role in Plant Defence

Glucosinolates are sulfur- and nitrogen-containing plant secondary metabolites common in the Brassicaceae and related plant families. Glucosinolates and their hydrolysis products are considered as potential components in the plant defence system against insects, herbivores and certain microbial pathogen. The first stage of the biosynthesis of aliphatic glucosinolates is chain elongation of methionine, in which additional methylene groups are inserted into the side chain. The first step of chain elongation in the biosynthesis of aliphatic glucosinolates, catalyzed by methylthioalkylmalate synthase (MAM), appears to be critical in regulating the products of this pathway. Two genes coding for this enzyme were identified in Arabidopsis thaliana ecotype Columbia, MAM1 and MAM-L. Both enzymes are capable to carry out the condensation reaction of the chain elongation cycle but differ in their substrate specificity. The aim of this study was to learn more about where the first step of the chain elongation of aliphatic glucosinolates occurs in an Arabidopsis plant by localizing transcripts and protein of MAM1 and MAM-L using Arabidopsis transgenic lines containing either GUS or GFP-fusion proteins with promoter or targeting sequence, respectively. Study of GUS expression showed promoter activity exclusively in the phloem part of the vascular bundles of roots, leaves, petioles and stems, while sub-cellular localisation did not exhibit the expected results due to weak signal of the targeting sequence-GFP making it impossible to draw a clear conclusion about the localization of the MAM enzymes. Analysis of transcript levels for MAM1 and MAM-L genes during different developmental stages were also presented. In order to get a better knowledge of the accumulation and involvement of glucosinolates in plant defence we also studied both, local and systemic glucosinolate response, after different biological treatments, pathogenic fungi and caterpillars, and chemical treatments, plant hormones and herbicides. The glucosinolate pattern found was similar for the herbicide and fungus treatments, and as well as for herbivore and methyl jasmonic acid treatment. All data strongly suggest that glucosinolates, play role in plant defence. Our study points out overlooked role of aliphatic glucosinolates in plant defence especially in the systemic defence response increasing the amount of potential toxic compounds in distant (systemic) but still healthy parts of the plant which might increase its fitness or at least help it to survive. Knowledge obtained in this study, the cellular and subcellular location of MAMs as well as accumulation site after some biological and chemical treatments will help in understanding how glucosinolate biosynthesis is regulated.

glucosinolates; methylthioalkylmalate synthase; cellular and subcellular localisation; fungi; caterpillars; methyl jasmonic acid; qRT-PCR

nije evidentirano