Molecular basis of resistance to sulfonylureas in Papaver rhoeas

A Papaver rhoeas population resistant to several acetolactate synthase (ALS) inhibiting herbicides, called 25/98, was found in Catalonia (Northeastern of Spain). This population has an altered form of the enzyme that showed cross-resistance to several herbicides of this group. The highest resistance was found with tribenuron-methyl and sulfometuron-methyl. Studies were conducted to define the molecular basis of this resistance. Two regions of the ALS gene were amplified using degenerated universal primers and sequenced. Population 25/98 contained a single nucleotide substitution in domain A changing Pro₁₉₇ by Ser (using the nomenclature of Arabidopsis thaliana) that confers sulfonylurea resistance. Another change was detected in a region located outside of any conserved domains described to date, but its implication in the resistance remains unclear. We analyze the putative role of the found mutations in relation to the observed resistance using a putative three-dimensional model of the Papaver ALS enzyme.