Comparative metabolomic analyses of two Ipomoea lacunosa biotypes with contrasting glyphosate tolerance elucidates glyphosate-induced differential perturbations in cellular physiology

Authors: MAROLI, AMITH - Clemson University; Nandula, Vijay; Duke, Stephen; GERARD, PATRICK - Clemson University; THARAYIL, NISHANTH - Clemson University

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2017
Publication Date: 12/26/2017
Citation: Maroli, A.S., Nandula, V.K., Duke, S.O., Gerard, P., Tharayil, N. 2017. Comparative metabolomic analyses of two Ipomoea lacunosa biotypes with contrasting glyphosate tolerance elucidates glyphosate-induced differential perturbations in cellular physiology. Journal of Agricultural and Food Chemistry. (66):2027-2039.

Interpretive Summary: Metabolomics is a reliable technique to identify innate physiological differences between plant biotypes as well as charting stress mitigation strategies. Scientists from the Crop Production Systems Research Unit, USDA-ARS, Stoneville, MS, other USDA-ARS research units, and Clemson University used non-targeted metabolic profiling to capture differences in metabolic abundances in two biotypes of pitted morningglory with varying tolerance to glyphosate (WAS and QUI biotypes). The metabolic differences significantly influenced 16 metabolic pathways in the WAS biotype. When exposed to a sub lethal glyphosate rate of 80 g ae/ha, both biotypes exhibited metabolic distresses. No changes in aromatic amino abundance was observed in the QUI biotype while a 133% increase in tyrosine (an aromatic amino acid) abundance was observed in the WAS biotype, indicating its tolerance to glyphosate. The less glyphosate tolerant QUI biotype had higher proline (stress response) levels and lower decrease in sugar content (movement of glyphosate to target sinks along photosynthate transport pathway) compared to the more tolerant WAS biotype. The reduced import of sugars from source to sink in these biotypes could be incidental to restricted glyphosate movement towards meristematic tissues. The results from this study imply that despite tolerance to glyphosate, the cellular metabolism of both biotypes is perturbed when exposed to sub lethal rates of glyphosate.

Technical Abstract: Metabolome profiling is a reliable technique to identify innate physiological differences between plant biotypes as well as charting stress mitigation strategies. In this study, we used non-targeted metabolic profiling to capture differences in metabolic abundances in two biotypes of pitted morningglory with varying tolerance to glyphosate [WAS (GR50 = 151 g ae/ha) and QUI (GR50 = 59 g ae/ha)]. Metabolic profiling followed by pathway topological analysis captured innate metabolic differences (22 significantly different metabolites) between WAS and QUI biotypes. These metabolic differences significantly influenced 16 metabolic pathways in the WAS biotype. Moreover, when exposed to a sub lethal glyphosate rate of 80 g ae/ha, both biotypes exhibited metabolic perturbations at 80 h after treatment. Shikimic acid accumulation in both the biotypes indicated 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) susceptibility. Despite EPSPS inhibition, no changes in aromatic amino abundance was observed in the QUI biotype while a 133% increase in Tyr abundance was observed in the WAS biotype, indicating its tolerance to the glyphosate. Compared to the respective water control, a 112% increase in the proline pool coupled with a 57% decrease in total sugar content was observed in the QUI biotype. In contrast, the WAS biotype had 69% increase in proline pool and 72% decrease in total sugar content. The reduced import of sugars from source to sink in these biotypes could be incidental to restricted glyphosate movement towards meristematic tissues. The results from this study imply that despite tolerance to glyphosate, the cellular metabolism of both biotypes is perturbed when exposed to sub lethal rates of glyphosate.