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The herbicides glyphosate and glufosinate are commonly used in citrus and sugarcane orchards in Guangxi Province, China, wherein the C 4 plant Eleusine indica (L.) Gaertn. is known to be a dominant weed species. However, high selection pressure has resulted in failure of control. In the present study, experiments were conducted to clarify resistance levels for the suspected populations and elucidate the mechanisms for multiple resistance. The resistance index to glyphosate was calculated for eight populations and ranged from 5.4 to 21.3, with a low-level shikimate content of 0.24-0.50 μg g -1 . In addition, three populations showed low-level resistance to glufosinate, with a resistance index ranging from 2.6 to 3.9. The amplification of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene with a double-mutation T102I + P106S (TIPS) or a single-mutation (P106S and P106A) was observed in most populations. The target genes of glufosinate (GS1-1, GS1-2, and GS1-3) showed high-level expression, namely 145.5-fold that of susceptible plants. The content of EPSPS and glutamine synthetase (GS) protein in resistant plants can reach to 3.6 and 2.1 times higher than those in susceptible plants, respectively. The overexpression of the EPSPS gene with double (T102I + P106S) or single (P106S and P106A) mutations, plus the overexpression of GS1-1, GS1-2, and GS1-3, responded to multiple resistance mechanisms. Altogether, these results demonstrate that overexpression of GS1 is a novel form of resistant mechanism to glufosinate in weeds., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Background: Developing herbicide-resistant (HR) crop cultivars is an efficient way to control weeds and minimize crop yield losses. However, widespread and long-term herbicide application has led to the evolution of resistant weeds. Here, we established a resistant (R) E. indica population, collected from imidazolinone-resistant rice cultivar fields., Results: The R population evolved 4.5-fold resistance to imazamox. Acetolactate synthase (ALS) gene sequencing and ALS activity assays excluded the effect of target-site resistance in this population. P450 inhibitor malathion pretreatment significantly reversed resistance to imazamox. RNA sequencing showed that a P450 gene CYP81A104 was expressed higher in R versus susceptible (S) plants. Arabidopsis overexpressing CYP81A104 showed resistance to ALS inhibitors (imazamox, tribenuron-methyl, penoxsulam and flucarbazone-sodium), PSII inhibitor (bentazone), hydroxyphenyl pyruvate dioxygenase inhibitor (mesotrione) and auxin mimics (MCPA), which was generally consistent with the results presented in the R population., Conclusion: This study confirmed that the CYP81A104 gene endowed resistance to multiherbicides with different modes-of-action. Our findings provide an insight into the molecular characteristics of resistance and contribute to formulating an appropriate strategy for weed management in HR crops. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

Intensive application of glyphosate has resulted in resistance evolution in many weed populations, including Eleusine indica . This study characterized glyphosate resistance and investigated the underlying mechanisms in a glyphosate-resistant population (R-JX) of E. indica from China. The R-JX population was 8.5 times resistant to glyphosate relative to the glyphosate-susceptible population (SA). Point mutations were not observed in the target gene 5-enolypyruvyl-shikimate-3-phosphate synthase gene ( EPSPS ). However, the expression level and copy number of EPSPS were 8.8 times and 15.2 times, respectively, greater in R-JX than that in the SA population. Pre-application of the P450 inhibitor lowered the resistance level to glyphosate from 8.5 times to 3.6 times in the R-JX population. RNA-Seq and RT-qPCR revealed that the CYP71AK44 gene was consistently upregulated in R-JX and five other glyphosate-resistant populations. Rice calli and seedlings overexpressing CYP71AK44 showed glyphosate resistance. In conclusion, overexpression of the target EPSPS plus CYP71AK44 collectively contributes to glyphosate resistance in these E. indica populations.

Eleusine indica is one of the most troublesome weeds in farmland worldwide, especially in Citrus Orchard of China. Glufosinate, as an efficient non-selective broad-spectrum herbicide, has been widely utilized for the control of E. indica in Citrus Orchard. The E. indica resistant population (R) was collected from a Citrus Orchard in Yichang City in Hubei province, China. Bioassay experiments showed that the R plants exhibited 3-fold resistance to glufosinate compared with the E. indica susceptible population (S). No known glutamine synthetase (GS) gene mutation associated with glufosinate resistance was found in R plants. And there was also no significant difference in GS activity between R and S plants. Those results indicated that the resistance to glufosinate in R did not involve target-site resistance. However, glutathione S-transferase (GST) inhibitor 4-chloro-7-nitrobenzoxadiazole (NBD-Cl) plus glufosinate gave a better control of R plants compared with glufosinate treatment alone. Moreover, both before and after glufosinate treatment, the GST activity in R plants was significantly higher than that in S plants. By RNA-seq, the expression of GSTU6 and GST4 up-regulated in R plants relative to S plants with or without glufosinate treatment. They were also significantly up-regulated expression in E. indica field resistant populations compared with S population. In summary, the study elucidated that R plants developed metabolic resistance to glufosinate involving GST. And GSTU6 and GST4 genes may play an important role in this glufosinate metabolic resistance. The research results provide a theoretical basis for a deeper understanding of resistance mechanism to glufosinate in E. indica., (Copyright © 2024. Published by Elsevier Inc.)