A novel psbA mutation (Phe274–Val) confers resistance to PSII herbicides in wild radish (Raphanus raphanistrum)

One particularly famous psbA gene mutation (Ser-264 Gly) has been known for decades. It has evolved in many parts of the world and gives resistance mainly to triazine herbicides but not to phenyl urea PS2 herbicides.

As well as identifying this Ser-264-Gly mutation in wild radish in Australia, in this work, Huan Lu identified a new mutation of the psbA gene, Phe-274-Val. This Phe-274-Val mutation endows modest resistance to triazines, metribuzin and to certain phenyl urea herbicides.

Background

Wild radish (Raphanus raphanistrum) is a globally important weed of crops. Two atrazine-resistant wild radish populations (R1 and R2), collected from the Western Australia grain belt, were investigated for resistance to photosystem II (PSII) herbicides.

Results

Sequencing of the full-length psbA gene revealed the well-known Ser264–Gly substitution in population R1, whereas population R2 displayed a novel Phe274–Val substitution. Herbicide dose–response studies confirmed that the population with the Ser264–Gly mutation exhibited high-level resistance to atrazine, but super-sensitivity to bromoxynil. Plants possessing the novel Phe274–Val mutation exhibited a modest level of resistance to atrazine, metribuzin and diuron, and were bromoxynil susceptible. Structural modelling of the mutant D1 proteins predicts that the Ser264–Gly mutation endows atrazine resistance by abolishing H-bonds, but confers bromoxynil super-sensitivity by enhancing hydrogen bonding. The Phe274–Val substitution provides resistance to atrazine and diuron by indirectly affecting H-bond formation between the Ser264 residue and the herbicides.

Conclusion

The results demonstrate that the Phe274–Val mutation is likely responsible for resistance to PSII-inhibiting triazine and urea herbicides.

To our knowledge, this is the first evidence of the psbA Phe274–Val mutation in wild radish conferring resistance to PSII herbicide