Overexpression of glutamine synthetases confers transgenic rice herbicide resistance

Glutamine synthetase (GS, E.C.6.3.1.2) is a key enzyme involved in the assimilation of inorganic nitrogen in higher plants and gram-negative microorganisms. GS is the targeting enzyme of a herbicide phosphinothricin (PPT)or Basta. In order to generate PPT-resistant transgenic rice via overexpression of GS, we constructed a plant expression vector p2GS harboring two different isoenzymes GS1 and GS2 cD-NAs under the control of constitutive promoters of rice Act1 and maize Ubiquitin(Ubi) genes. The p2GS was introduced into rice genome by Agrobacterium-mediated transformation and confirmed by PCR and Southern blot hybridization. GS-transgene expression was first detected by Northern blot analyses. Results from Basta test indicated that GS-transgenic plants can tolerate as high as 0.3% Basta solution. In addition, our results also demonstrated that GS overexpression conferred transformed rice calli PPT resistance. Thus, GS cassette can serve as a selective marker gene instead of bar cassette for selection of PPT transformants.