Herbicide resistance in Arabidopsis thaliana: Role of plant 
multidrug resistance transporter

Principal Investigator of the IST team: Isabel Sá-Correia

Contract: PTDC/AGR-AAM/67858/2006  

Start date: 01/07/2007

Duration: 36 months


The widespread use of herbicides has led to an increasing number of resistant weed species and classes of herbicides to which resistance has evolved, with some biotypes currently showing multiple-resistance to various of these agrochemicals. Herbicide resistance has the potential to cause not only large economic losses in agriculture, but also deleterious effects on the environment and human health, as a result of rising herbicide application rates. The lack of a basic understanding of the molecular mechanisms underlying herbicide resistance remains the greatest obstacle to the use of biotechnology to deal with this problem.
The Instituto de Biotecnologia e Química Fina, Instituto Superior Técnico (IBQF-IST) team has recently shown that three Saccharomyces cerevisiae genes encoding plasma membrane multiple drug resistance (MDR) transporters determine yeast resistance to 2,4-dichlorophenoxyacetic acid (2,4-D), one of the selective herbicides most successfully used worldwide. Two of these genes, ScPDR5 and ScPDR18, belong to the pleiotropic drug resistance (PDR) subfamily of ABC drug efflux pumps, whereas the other MDR transporter (ScTPO1) is a member of the major facilitator superfamily (MFS). Based on these findings, the Instituto Gulbenkian de Ciência (IGC) team has been analyzing the effects of 2,4-D application on the expression of poorly characterized Arabidopsis thaliana MDR transporter genes showing high sequence similarity to the yeast resistance determinants. First results show a clear transcriptional activation of three of these plant genes in response to the herbicide: two PDR genes, AtPDR8 and AtPDR14, and the MFS gene At5g13750. This strongly suggests an involvement of these putative plasma membrane drug efflux pumps in the plant’s response to herbicidal concentrations of 2,4-D and pinpoints excellent candidates for herbicide resistance determinants in A. thaliana.
The IGC and IBQF-IST groups will collaborate in this project to investigate the role of genes encoding MDR transporters of the ABC and MF Superfamilies in plant herbicide resistance. The functional characterization of these novel or poorly characterized plant genes will involve gene expression analysis and reverse genetic approaches in Arabidopsis, heterologous expression and complementation experiments in yeast, and membrane transport assays in both systems. These studies, using the plant model A. thaliana and the fundamental model eukaryote S. cerevisiae, will accelerate understanding of the molecular mechanisms governing herbicide resistance, currently one of the most unexplored and exciting topics in plant biology, with important implications for agriculture, the environment, and human health.