Mechanism of Resistance to Pyroxsulam in Multiple-Resistant Alopecurus myosuroides from China

Common agricultural weeds among alien invasive plants in China: Species lists and their practical managing strategies

Plant invasion is a big challenge to weed management of agricultural lands. In order to reveal the list of common weed species among alien invasive plants, and reveal practical management strategies, we extracted the species lists of common alien agricultural weeds (CAAWs) of various arable lands and plantations, by comparing the lists of alien invasive plant species and common weed species published in China. Totally 88 species from 18 families were recognized as CAAWs, among which 43.0 % are native to North America, followed by South America (34.4 %), Europe (29.0 %), Asia (23.7 %) and Africa (17.2 %); 62.4 % were introduced into China from 1840 to 1949. CAAWs such as Aegilops tauschii Coss., Alopecurus myosuroides Huds., Lolium multiflorum Lamk, Avena fatua L., Phalaris minor Retz, Phalaris paradoxa L., Veronica persica Poir., Geranium carolinianum L., Ranunculus muricatus L., and Cerastium glomeratum Thuill. frequently infest highlands with summer-ripe crops such as wheat and oilseed rape; Alternanthera spp., Panicum repens L., Paspalum conjugatum Bergius, and Ageratum conyzoides L. frequently infest highlands with autumn-ripe crops; and Paspalum distichum L., Alternanthera philoxeroides, and Ammannia coccinea Rott. occasionally infest rice fields. Troublesome CAAWs in plantations in China mainly consist of tall herbs, and climbing or spiny plants, such as Mikania micrantha Kunth, Ipomoea spp., Solidago canadensis L., Erigeron spp. and Bidens spp. Management strategies against CAAWs in current China mainly rely on chemical control, tillage, soil mulching, and manual removing of weeds. Next, effective risk assessing models targeting to different sorts of arable lands or plantations are urgently needed; as well, effective, feasible and sustainable integrated management strategies against troublesome CAAWs should be developed and applied.

Chromosome-scale genome assembly and de novo annotation of Alopecurus aequalis

Alopecurus aequalis is a winter annual or short-lived perennial bunchgrass which has in recent years emerged as the dominant agricultural weed of barley and wheat in certain regions of China and Japan, causing significant yield losses. Its robust tillering capacity and high fecundity, combined with the development of both target and non-target-site resistance to herbicides means it is a formidable challenge to food security. Here we report on a chromosome-scale assembly of A. aequalis with a genome size of 2.83 Gb. The genome contained 33,758 high-confidence protein-coding genes with functional annotation. Comparative genomics revealed that the genome structure of A. aequalis is more similar to Hordeum vulgare rather than the more closely related Alopecurus myosuroides.

The Cys-2088-Arg mutation in the ACCase gene and enhanced metabolism confer cyhalofop-butyl resistance in Chinese sprangletop (Leptochloa chinensis)

Acetyl-CoA carboxylase (ACCase)-inhibiting herbicides are among the most commonly used herbicides to control grassy weeds, especially Leptochloa chinensis, in rice fields across China. Herein, we collected a suspected resistant (R) population of L. chinensis (HFLJ16) from Lujiang county in Anhui Province. Whole plant dose response tests showed that, compared with the susceptible (S) population, the R population showed high resistance to cyhalofop-butyl (22-fold) and displayed cross-resistance to metamifop (9.7-fold), fenoxaprop-P-ethyl (18.7-fold), quizalofop-P-ethyl (7.6-fold), clodinafop-propargyl (12-fold) and clethodim (8.4-fold). We detected an amino acid substitution (Cys-2088-Arg) in the ACCase of resistant L. chinensis. However, ACCase gene expression levels were not significantly different (P > 0.05) between R plants and S plants, without or with cyhalofop-butyl treatment. Furthermore, pretreatment with piperonyl butoxide (PBO, a cytochrome P450 monooxygenase (CYP450) inhibitor) or 4-chloro-7-nitrobenzoxadiazole (NBD-Cl, a glutathione-S-transferase (GST) inhibitor), inhibited the resistance of the R population to cyhalofop-butyl significantly (by approximately 60% and 26%, respectively). Liquid chromatography tandem mass spectrometry analysis showed that R plants metabolized cyhalofop-butyl and cyhalofop acid (its metabolite) significantly faster than S plants. Three CYP450 genes, one GST gene, and two ABC transporter genes were induced by cyhalofop-butyl and were overexpressed in the R population. Overall, GST-associated detoxification, CYP450 enhancement, and target-site gene mutation are responsible for the resistance of L. chinensis to cyhalofop-butyl.

Comprehensive insights into herbicide resistance mechanisms in weeds: a synergistic integration of transcriptomic and metabolomic analyses

Omics techniques, including genomics, transcriptomics, proteomics, and metabolomics have smoothed the researcher's ability to generate hypotheses and discover various agronomically relevant functions and mechanisms, as well as their implications and associations. With a significant increase in the number of cases with resistance to multiple herbicide modes of action, studies on herbicide resistance are currently one of the predominant areas of research within the field of weed science. High-throughput technologies have already started revolutionizing the current molecular weed biology studies. The evolution of herbicide resistance in weeds (particularly via non-target site resistance mechanism) is a perfect example of a complex, multi-pathway integration-induced response. To date, functional genomics, including transcriptomic and metabolomic studies have been used separately in herbicide resistance research, however there is a substantial lack of integrated approach. Hence, despite the ability of omics technologies to provide significant insights into the molecular functioning of weeds, using a single omics can sometimes be misleading. This mini-review will aim to discuss the current progress of transcriptome-based and metabolome-based approaches in herbicide resistance research, along with their systematic integration.

Integrated transcriptomic and metabolomic analyses of the molecular mechanisms of two highland barley genotypes with pyroxsulam responses

Highland barley is one of the few crops that can be grown at high elevations, making it a key resource within the Tibet Plateau. Weeds are a significant threat to highland barley production, and new herbicides and tolerant barley varieties are needed to control this ever-growing problem. A better understanding of existing herbicide resistance mechanisms is therefore needed. In this study, transcriptomic and metabolomic analyses were used to identify molecular and physiological changes in two highland barley genotypes with differing sensitivities to the herbicide pyroxsulam. We identified several stress-responsive metabolites, including flavonoids and antioxidants, which accumulated to significantly higher levels in the pyroxsulam-resistant genotype. Additionally, we found key genes in both the flavonoid biosynthesis pathway and the antioxidant system that were up-regulated in pyroxsulam-resistant barley. This work significantly expands on the current understanding of the molecular mechanisms underlying differing pyroxsulam tolerance among barley genotypes and provides several new avenues to explore for breeding or engineering tolerant barley.