ORIGINAL ABSTRACT

Glyphosate is a broad-spectrum herbicide that kills most vascular plant weeds but is ineffective against many bryophytes. Glyphosate competitively inhibits the enolpyruvyl transferase enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). EPSPS catalyzes the production of 5-enolpyruvylshikimate-3-phosphate (EPSP)-an intermediate in the shikimate pathway-from shikimate-3-phosphate (S3P) and phosphoenolpyruvate (PEP) substrates. Here, we show that Marchantia polymorpha mutants with loss-of-function mutations in a closely related enolpyruvyl transferase, MpMurA, were more sensitive to glyphosate than wild-type controls. Overexpression of MpMurA in M. polymorpha increased glyphosate tolerance, and heterologous expression of the M. polymorpha MurA enzyme in Arabidopsis thaliana conferred glyphosate resistance. Furthermore, we demonstrate that MpMurA catalyzes the production of EPSP from S3P and PEP substrates. These data demonstrate that MpMurA contributes to glyphosate tolerance in M. polymorpha. We speculate that the existence of two independent mechanisms for EPSP synthesis-one canonical and EPSPS-dependent, and the other MurA-dependent-may account for glyphosate tolerance in bryophytes. Alternatively, MurA in bryophytes may bind glyphosate, thereby leaving more unbound EPSPS enzymes available, allowing aromatic amino acid biosynthesis to continue.