Foliar glyphosate treatment alters transcript and hormone profiles in crown buds of leafy spurge and induces dwarfed and bushy phenotypes throughout its perennial life cycle

Authors: Dogramaci, Munevver; Anderson, James; Chao, Wun; Horvath, David; HERNANDEZ, ALVARO - University Of Illinois; MIKEL, MARK - University Of Illinois; Foley, Michael

Submitted to: The Plant Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2017
Publication Date: 5/9/2017
Citation: Dogramaci, M., Anderson, J.V., Chao, W.S., Horvath, D.P., Hernandez, A.G., Mikel, M.A., Foley, M.E. 2017. Foliar glyphosate treatment alters transcript and hormone profiles in crown buds of leafy spurge and induces dwarfed and bushy phenotypes throughout its perennial life cycle. The Plant Genome. https://doi.org/10.3835/plantgenome2016.09.0098.
DOI: https://doi.org/10.3835/plantgenome2016.09.0098

Interpretive Summary: Leafy spurge is an invasive perennial weed infesting rangelands and non-cultivated areas in the Great Plains of the US and Canada. Long term control of leafy spurge requires continual herbicide applications because the plant reproduces vegetatively from abundant underground buds. We are investigating whether sublethal glyphosate rates, relative to non-treated controls, affect the transition of the underground buds through the three seasonally-regulated phase of bud dormancy (i.e., para-, endo-, and eco-dormancy). Based on dormancy marker genes and statistical techniques we determined that the buds of glyphosate-treated plants transitioned through endo- and eco-dormancy. Additionally, glyphosate treatment increased shikimate abundance in buds 7d post-treatment, but the abundance of shikimate gradually decreased as buds transitioned through endo- and eco-dormancy. This observation suggests that the target site of glyphosate was no-longer affected although the stunted and bushy phenotype of glyphosate treated leafy spurge shoots persisted. Transcript profiles further indicated that glyphosate significant affected plant hormone biosynthesis/signaling pathways, and these data correlated well with abundance of several hormones.

Technical Abstract: Leafy spurge (Euphorbia esula) is an invasive weed of North America and its perennial nature is attributed to underground adventitious buds (UABs) that undergo seasonal cycles of para-, endo- and eco-dormancy. Recommended field rates of glyphosate (~1 kg/ha) destroys above-ground shoots of leafy spurge, but plants still regenerates vegetatively; therefore it has been considered glyphosate tolerant. However, foliar application of glyphosate at higher rates (2.2-6.7 kg/ha) causes sublethal effects that induce UABs to produce stunted and bushy phenotypes. We investigated effects of glyphosate treatment (±2.24 kg/ha) on vegetative growth, metabolite and transcript profiles in UABs under controlled environments during the perennial life cycle. Because shoots derived from UABs of glyphosate-treated plants produced stunted and bushy phenotypes, we could not directly determine if these UABs transitioned through seasonally-induced endo- and eco-dormancy, similar to the untreated controls. However, transcript abundance for leafy spurge dormancy marker genes (HY5, MAF3-like, RD22, RVE1-like) and principal component analyses suggested that UABs of glyphosate-treated plants transitioned through endo- and eco-dormancy. Glyphosate treatment increased shikimate abundance in UABs 7d post-treatment; however, abundance of shikimate gradually decreased as UABs transitioned through endo- and eco-dormancy. The dissipation of shikimate overtime in UABs likely suggests the target site of glyphosate was no-longer affected, but these changes did not reverse the altered phenotypes observed from UABs of glyphosate treated leafy spurge. Transcript profiles further indicated that glyphosate significant affected phytohormone biosynthesis/signaling pathways, and abundance of auxins, abscisic acid, and cytokinins correlated well with the transcript data and the altered phenotypes.