title: Mechanism of glyphosate control of Phelipanche aegyptiaca.
abstract: Despite its total reliance on its host plant, the holoparasite Phelipanche aegyptiaca suffers from a deficiency of aromatic amino acids upon exposure to glyphosate. The herbicide glyphosate inhibits 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), a key enzyme in the biosynthesis of aromatic amino acids. However, the functionality of the EPSPS pathway in the obligate root holoparasite Phelipanche aegyptiaca is not straightforward because of the parasite's total dependence on the host plant. Despite the importance of glyphosate as a means of controlling P. aegyptiaca, the mechanism of action of the herbicide in this parasite is not clearly understood. We characterized glyphosate control of P. aegyptiaca by using a glyphosate-resistant tomato (GRT) genotype as the host plant and evaluating the activity of EPSPS and the levels of free aromatic amino acids in the parasite. The viability of the parasite's tissues deteriorated within the first 40 h after treatment (HAT) with glyphosate. In parallel, shikimate accumulation in the parasite was first detected at 24 HAT and increased over time. However, shikimate levels in the GRT host did not increase, indicating that the host was indeed glyphosate tolerant. Free phenylalanine and tyrosine levels decreased by 48 HAT in the parasite, indicating a deficiency of aromatic amino acids. The use of GRT as the host enabled us to observe, in an in situ experimental system, both endogenous EPSPS inhibition and a deficiency of aromatic amino acids in the parasite. We thus provided evidence for the presence of an active EPSPS and aromatic amino acid biosynthesis pathway in P. aegyptiaca and pinpointed this pathway as the target of glyphosate action in this parasite.
authors.affiliation: Department of Plant Pathology and Weed Research, Agricultural Research Organization (ARO), Newe Ya'ar Research Center, Ramat Yishay, Israel. tal2@volcani.agri.gov.il.|The Robert H. Smith Institute of Plant Sciences and Genetics, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel. tal2@volcani.agri.gov.il.
authors.forename: Tal
authors.initials: T
authors.lastname: Shilo
authors.affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
authors.forename: Lilach
authors.initials: L
authors.lastname: Zygier
authors.affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
authors.forename: Baruch
authors.initials: B
authors.lastname: Rubin
authors.affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
authors.forename: Shmuel
authors.initials: S
authors.lastname: Wolf
authors.affiliation: Department of Plant Pathology and Weed Research, Agricultural Research Organization (ARO), Newe Ya'ar Research Center, Ramat Yishay, Israel.
authors.forename: Hanan
authors.initials: H
authors.lastname: Eizenberg
mesh_terms: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase / Q000378:metabolism; D053898:Biosynthetic Pathways / Q000187:drug effects; D005453:Fluorescence; D005998:Glycine / Q000031:analogs & derivatives* / Q000633:toxicity; D053209:Herbicide Resistance; D016014:Linear Models; D018551:Solanum lycopersicum / Q000187:drug effects / Q000469:parasitology; D055442:Metabolome / Q000187:drug effects; D031670:Orobanchaceae / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development / Q000502:physiology*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D012765:Shikimic Acid / Q000378:metabolism; D000097797:Glyphosate
chemical_list: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase; D005998:Glycine; D012765:Shikimic Acid; D000097797:Glyphosate
keywords: Amino acids; Broomrape; EPSP synthase; EPSPS; Shikimate; Tomato