Physiological and Molecular Characterization of Hydroxyphenylpyruvate Dioxygenase (HPPD)-inhibitor Resistance in Palmer Amaranth (Amaranthus palmeri S.Wats.)

Abstract

Herbicides that inhibit hydroxyphenylpyruvate dioxygenase (HPPD) such as mesotrione are widely used to control a broad spectrum of weeds in agriculture. Amaranthus palmeri is an economically troublesome weed throughout the United States. The first case of evolution of resistance to HPPD-inhibiting herbicides in A. palmeri was documented in Kansas (KS) and later in Nebraska (NE). The objective of this study was to investigate the mechansim of HPPD-inhibitor (mesotrione) resistance in A. palmeri. Dose response analysis revealed that this population (KSR) was 10–18 times more resistant than their sensitive counterparts (MSS or KSS). Absorbtion and translocation analysis of [14C] mesotrione suggested that these mechanisms were not involved in the resistance in A. palmeri. Importantly, mesotrione (>90%) was detoxified markedly faster in the resistant populations (KSR and NER), within 24 hours after treatment (HAT) compared to sensitive plants (MSS, KSS, or NER). However, at 48 HAT all populations metabolized the mesotrione, suggesting additional factors may contribute to this resistance. Further evaluation of mesotrione-resistant A. palmeri did not reveal any specific resistance-conferring mutations nor amplification of HPPD gene, the molecular target of mesotrione. However, the resistant populations showed 4- to 12-fold increase in HPPD gene expression. This increase in HPPD transcript levels was accompanied by increased HPPD protein expression. The significant aspects of this research include: the mesotrione resistance in A. palmeri is conferred primarily by rapid detoxification (non-target-site based) of mesotrione; additionally, increased HPPD gene expression (target-site based) also contributes to the resistance mechanism in the evolution of herbicide resistance in this naturally occurring weed species.

Tembotrione detoxification in 4‐hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor‐resistant Palmer amaranth (Amaranthus palmeri S. Wats.)

“…In 2009, the first case of A. palmeri resistance to HPPD inhibitors (mesotrione, topramezone, and tembotrione) was reported from a corn and sorghum ( Sorghum bicolor ) field in Kansas. The reported biotype was also resistant to ALS and PS II inhibitors . Additional cases of HPPD inhibitor resistance in the same species were later reported from Nebraska in 2011 and 2014, with the latter biotype also resistant to ALS and PS II inhibitors .…”

“…The reported biotype was also resistant to ALS and PS II inhibitors . Additional cases of HPPD inhibitor resistance in the same species were later reported from Nebraska in 2011 and 2014, with the latter biotype also resistant to ALS and PS II inhibitors . Resistance to HPPD inhibitors has been reported in common waterhemp ( Amaranthus tuberculatus var.…”

“…NER was not controlled by atrazine, or by the HPPD inhibitors mesotrione, tembotrione, and topramezone . Two previous studies used HPPD‐resistant A. palmeri collected from the same field but NER was collected at a different time . For all following experiments, the seed was sown in plant tissue culture containers (PlantCon; MP Biomedicals, LLC, Santa Ana, CA, USA) containing 0.7% agar type A (Sigma‐Aldrich, St. Louis, MO, USA), kept in the dark for 2 days at 4 °C, and then germinated in a growth chamber at 28 °C and 16:8 h light:dark conditions at 400 µmol m −2 s −1 and 70% humidity.…”

Reversing resistance to tembotrione in an Amaranthus tuberculatus (var. rudis) population from Nebraska, USA with cytochrome P450 inhibitors

“…This type of herbicide resistance has been reported in only two Amaranthus species. Two A. palmeri biotypes from Kansas and Nebraska evolved resistance to mesotrione via a metabolism‐based mechanism, as well as increased gene transcription and protein expression . The A. palmeri biotype from Nebraska was also resistant to tembotrione via enhanced metabolism .…”

First report of Ser653Asn mutation endowing high‐level resistance to imazamox in downy brome (Bromus tectorum L.)

“…In addition to target site mutations, non‐target site‐based resistance mechanisms, primarily the enhanced rate of metabolism mediated by cytochrome P450 monooxygenases, has also been reported in several ALS‐resistant weed biotypes . Furthermore, it is not uncommon to acquire both target and non‐target site resistance mechanisms to ALS inhibitors in a single population or in a same plant, as previously observed in ALS‐resistant common waterhemp ( Amaranthus tuberculatus ) and Palmer amaranth ( Amaranthus palmeri ) …”