Sulfonyl urea resistance is due to mutation in:
Acetolactate synthase also called acetohydroxyacid synthase catalyzes first common step of branched-chain amino acid biosynthesis: condensation of two pyruvate molecules to acetolactate leading to valine and leucine, and condensation of pyruvate and 2-ketobutyrate to acetohydroxybutyrate leading to isoleucine. Sulfonylurea herbicides such as chlorsulfuron and tribenuron bind in substrate access channel of ALS, blocking access to catalytic site containing thiamine pyrophosphate. Resistance evolves via non-synonymous mutations in ALS gene altering herbicide binding pocket without abolishing cata
Ref: LaRossa Trends Biotech 1984 ALS mutation; Tranel Weed Sci 2002 ALS Pro197; NCBI NBK21601; PubMed 14769484 sulfonylurea resistance mechanism review.