Yeast of Eden: microbial resistance to glyphosate from a yeast perspective

Abstract

First marketed as RoundUp, glyphosate is history’s most popular herbicide because of its low acute toxicity to metazoans and broad-spectrum effectiveness across plant species. The development of glyphosate-resistant crops has led to increased glyphosate use and consequences from the use of glyphosate-based herbicides (GBH). Glyphosate has entered the food supply, spurred glyphosate-resistant weeds, and exposed non-target organisms to glyphosate. Glyphosate targets EPSPS/AroA/Aro1 (orthologs across plants, bacteria, and fungi), the rate-limiting step in the production of aromatic amino acids from the shikimate pathway. Metazoans lacking this pathway are spared from acute toxicity and acquire their aromatic amino acids from their diet. However, glyphosate resistance is increasing in non-target organisms. Mutations and natural genetic variation discovered in Saccharomyces cerevisiae illustrate similar types of glyphosate resistance mechanisms in fungi, plants, and bacteria, in addition to known resistance mechanisms such as mutations in Aro1 that block glyphosate binding (target-site resistance (TSR)) and mutations in efflux drug transporters non-target-site resistance (NTSR). Recently, genetic variation and mutations in an amino transporter affecting glyphosate resistance have uncovered potential off-target effects of glyphosate in fungi and bacteria. While glyphosate is a glycine analog, it is transported into cells using an aspartic/glutamic acid (D/E) transporter. The size, shape, and charge distribution of glyphosate closely resembles D/E, and, therefore, glyphosate is a D/E amino acid mimic. The mitochondria use D/E in several pathways and mRNA-encoding mitochondrial proteins are differentially expressed during glyphosate exposure. Mutants downstream of Aro1 are not only sensitive to glyphosate but also a broad range of other chemicals that cannot be rescued by exogenous supplementation of aromatic amino acids. Glyphosate also decreases the pH when unbuffered and many studies do not consider the differences in pH that affect toxicity and resistance mechanisms.

In situ monitoring of the shikimate pathway: a combinatorial approach of Raman reverse stable isotope probing and hyperspectral imaging

“…This corresponds to the fact that these peaks have changed over time due to the active shikimate pathway resulting in the turnover of nascent aromatic acids. In contrast, we observed strong auto peaks at 967, 1317 and 622 cm −1 in the treated group, which supports the observation that the 13 C-labelled peak has undergone significant changes with time. Furthermore, we observed a negative cross peak for 13 C-labelled and an unlabelled aromatic amino acid peak position in the untreated group.…”

“…In contrast, we observed strong auto peaks at 967, 1317 and 622 cm −1 in the treated group, which supports the observation that the 13 C-labelled peak has undergone significant changes with time. Furthermore, we observed a negative cross peak for 13 C-labelled and an unlabelled aromatic amino acid peak position in the untreated group. This shows the negative correlation between two peak positions, that is, the dynamics is in opposite directions, which supports the fact that shikimate pathway activity takes place in cells.…”

“…Glyphosate (N-[ phosphonomethyl]-glycine) is a well-known inhibitor of the shikimate pathway in E. coli. 13,14 To check the inhibitory action of glyphosate, OD 600 values from the treated culture were plotted against the incubation time, as shown in Fig. S1.…”

“…7 Raman spectroscopy is an efficient label-free, reagent-free, and nondestructive analytical tool for analysing biomolecules in situ. Stable isotope probes, such as 2 H, 13 C, 15 N, and 18 O, can be used as tags for analysing the de novo biosynthesis of different biomolecules simultaneously using Raman spectroscopy. When the parent atom is replaced by its heavier isotope, the reduced mass increases.…”

The low mutational flexibility of the EPSP synthase in Bacillus subtilis is due to a higher demand for shikimate pathway intermediates

“…The intensive use of GS in agriculture has led to the development of resistance to the herbicide in bacteria, fungi and plants (Funke et al, 2006;Powles, 2008;Shaner et al, 2012;Sammons & Gaines, 2014;Chekan et al, 2016;Hertel et al, 2021;Molina-Santiago & Udaondo, 2022;Patriarcheas et al, 2023). For instance, the modification of the GS target through the acquisition of mutations in the EPSP synthase gene is a widespread resistance mechanism (Barry et al, 1992;Chekan et al, 2016;Comai et al, 1983;Della-Cioppa et al, 1987).…”