Triple mechanisms of glyphosate-resistance in a naturally occurring glyphosate-resistant plant Dicliptera chinensis

Dicliptera chinensis Juss. is a unique annual plant that is naturally resistant to the herbicide glyphosate. We reported here the characterization of its 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), the target of glyphosate action. In comparison to the glyphosate-sensitive weed Ageratum houstonianum, D. chinensis had higher EPSPS activity, even before glyphosate treatment. Glyphosate treatment caused a significant increase in the EPSPS mRNA and protein level. This increase was apparent at approximate to 8 h of glyphosate treatment and peaked at approximate to 16 h. The rapid time-course suggested that the increase is not due to gene amplification. The higher endogenous EPSPS activity and the induction by glyphosate could probably explain the resistance to glyphosate. Two cDNAs representing two distinct EPSPS genes were isolated. Their sequences were highly homologous to the known plant and bacterial EPSPS. Northern and Western blot analyses revealed differential tissue distribution. Our analysis of mRNA and protein expression also suggested possible posttranscriptional regulation. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.