SummaryRapid detoxification of atrazine in naturally tolerant crops such as maize (Zea mays) and grain sorghum (Sorghum bicolor) results from glutathione S‐transferase (GST) activity. In previous research, two atrazine‐resistant waterhemp (Amaranthus tuberculatus) populations from Illinois, U.S.A. (designated ACR and MCR), displayed rapid formation of atrazine‐glutathione (GSH) conjugates, implicating elevated rates of metabolism as the resistance mechanism. Our main objective was to utilize protein purification combined with qualitative proteomics to investigate the hypothesis that enhanced atrazine detoxification, catalysed by distinct GSTs, confers resistance in ACR and MCR. Additionally, candidate AtuGST expression was analysed in an F2 population segregating for atrazine resistance. ACR and MCR showed higher specific activities towards atrazine in partially purified ammonium sulphate and GSH affinity‐purified fractions compared to an atrazine‐sensitive population (WCS). One‐dimensional electrophoresis of these fractions displayed an approximate 26‐kDa band, typical of GST subunits. Several phi‐ and tau‐class GSTs were identified by LC‐MS/MS from each population, based on peptide similarity with GSTs from Arabidopsis. Elevated constitutive expression of one phi‐class GST, named AtuGSTF2, correlated strongly with atrazine resistance in ACR and MCR and segregating F2 population. These results indicate that AtuGSTF2 may be linked to a metabolic mechanism that confers atrazine resistance in ACR and MCR.

Waterhemp [Amaranthus tuberculatus (Moq) Sauer] is a difficult‐to‐control dicot weed in the United States. Atrazine [6‐chloro‐N‐ethyl‐N’‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] is commonly used for preemergence (PRE) and postemergence (POST) waterhemp control in maize (Zea mays L.). Previous research reported that atrazine metabolism via glutathione S‐transferase (GST) activity contributes to atrazine POST resistance in two waterhemp populations from Illinois, designated MCR (McLean County, Illinois, resistant) and ACR (Adams County, Illinois, resistant). Objectives were to quantify responses of these populations to atrazine PRE and determine if the combination of a GST inhibitor and atrazine PRE or POST increases their control. Dose‐response analyses indicated MCR was resistant to atrazine PRE relative to ACR or WCS (Wayne County sensitive; herbicide‐sensitive population), despite MCR and ACR exhibiting equivalent levels of atrazine resistance POST. The ACR response to atrazine PRE (LD50) was intermediate compared with MCR and WCS. Seedling survival of ACR was reduced by 4‐chloro‐7‐nitrobenzofurazan (NDB‐Cl; a GST inhibitor) and atrazine PRE more than atrazine PRE alone, but not in MCR. Atrazine following NBD‐Cl applied POST inhibited seedling growth in ACR, but not in MCR. Enhanced atrazine activity with NBD‐Cl further supports rapid metabolism via GSTs as the main atrazine‐resistance mechanism in ACR. GST(s) that metabolize atrazine in MCR may not have been completely inhibited by NBD‐Cl, indicating that similar yet distinct atrazine‐resistance mechanisms exist in MCR compared to ACR. In conclusion, atrazine PRE (with or without NBD‐Cl) still controls ACR when applied at typical field‐use rates in maize, but the length of residual activity may be shorter than in sensitive populations.Core Ideas Two waterhemp populations are resistant to atrazine POST due to increased metabolism by GST enzymes. Since atrazine can also be soil applied, quantifying the levels of resistance in these populations is important for weed management in maize. The MCR population was resistant to atrazine PRE and displayed a higher level of resistance to atrazine PRE than the ACR population. NBD‐Cl, a metabolic inhibitor of GST enzymes, enhanced atrazine activity in the ACR population but not MCR. The length of residual activity of atrazine may be shorter for controlling these populations in maize compared with sensitive populations.

Digestion of plant cell wall polysaccharides is important in energy capture in the gastrointestinal tract of many herbivorous and omnivorous mammals, including humans and ruminants. The members of the genus Ruminococcus are found in both the ruminant and human gastrointestinal tract, where they show versatility in degrading both hemicellulose and cellulose. The available genome sequence of Ruminococcus albus 8, a common inhabitant of the cow rumen, alludes to a bacterium well-endowed with genes that target degradation of various plant cell wall components. The mechanisms by which R. albus 8 employs to degrade these recalcitrant materials are, however, not clearly understood. In this report, we demonstrate that R. albus 8 elaborates multiple cellobiohydrolases with multi-modular architectures that overall enhance the catalytic activity and versatility of the enzymes. Furthermore, our analyses show that two cellobiose phosphorylases encoded by R. albus 8 can function synergistically with a cognate cellobiohydrolase and endoglucanase to completely release, from a cellulosic substrate, glucose which can then be fermented by the bacterium for production of energy and cellular building blocks. We further use transcriptomic analysis to confirm the over-expression of the biochemically characterized enzymes during growth of the bacterium on cellulosic substrates compared to cellobiose.