Is the protection of photosynthesis related to the mechanism of quinclorac resistance in Echinochloa crus-galli var. zelayensis?

Proteomic Analysis Comparison on the Ecological Adaptability of Quinclorac-Resistant Echinochloa crus-galli

Barnyardgrass (Echinochloa crus-galli L.) is the most serious weed threatening rice production, and its effects are aggravated by resistance to the quinclorac herbicide in the Chinese rice fields. This study conducted a comparative proteomic characterization of the quinclorac-treated and non-treated resistant and susceptible E. crus-galli using isobaric tags for relative and absolute quantification (iTRAQ). The results indicated that the quinclorac-resistant E. crus-galli had weaker photosynthesis and a weaker capacity to mitigate abiotic stress, which suggested its lower environmental adaptability. Quinclorac treatment significantly increased the number and expression of the photosynthesis-related proteins in the resistant E. crus-galli and elevated its photosynthetic parameters, indicating a higher photosynthetic rate compared to those of the susceptible E. crus-galli. The improved adaptability of the resistant E. crus-galli to quinclorac stress could be attributed to the observed up-regulated expression of eight herbicide resistance-related proteins and the down-regulation of two proteins associated with abscisic acid biosynthesis. In addition, high photosynthetic parameters and low glutathione thiotransferase (GST) activity were observed in the quinclorac-resistant E. crus-galli compared with the susceptible biotype, which was consistent with the proteomic sequencing results. Overall, this study demonstrated that the resistant E. crus-galli enhanced its adaptability to quinclorac by improving the photosynthetic efficiency and GST activity.

Comparative Analysis of Whole Chloroplast Genomes of Three Common Species of Echinochloa (Gramineae) in Paddy Fields

Echinochloa crus-galli var. crus-galli, E. crus-galli var. zelayensis, and E. glabrescens, morphologically similar at the seedling stage, are the most pernicious barnyard grass species in paddy fields worldwide. Chloroplast (cp) genomes could be conducive to their identification. In this study, we assembled the complete cp genome sequences of Echinochloa crus-galli var. crus-galli (139,856 bp), E. crus-galli var. zelayensis (139,874 bp), and E. glabrescens (139,874 bp), which exhibited a typical circular tetramerous structure, large and small single-copy regions, and a pair of inverted repeats. In Echinochloa crus-galli var. crus-galli, there were 136 simple sequence (SSRs) and 62 long (LRs) repeats, and in the other two species, 139 SSRs and 68 LRs. Each cp genome contains 92 protein-encoding genes. In Echinochloa crus-galli var. crus-galli and E. glabrescens, 321 and 1 single-nucleotide polymorphisms were detected compared to Echinochloa crus-galli var. zelayensis. IR expansion and contraction revealed small differences between the three species. The phylogenetic tree based on cp genomes demonstrated the phylogenetic relationship between ten barnyard grass species and other common Gramineae plants, showing new genetic relationships of the genus Echinochloa. This study provides valuable information on cp genomes, useful for identifying and classifying the genus Echinochloa and studying its phylogenetic relationships and evolution.

Amelioration of sodium and arsenic toxicity in Salvinia natans L. with 2,4-D priming through physiological responses

Sodium (Na) and arsenic (As) toxicity were monitored by hyperaccumulation of metals in Salvinia natans L. with 2,4-dichlorophenoxyacetic acid (2,4-D) induction. Salvinia was recorded with significant bioaccumulation of those metals with de-folding of cellular attributes in sustenance under toxic environment. 2,4-D priming has revised the growth components like net assimilation rate and relative water content to register initial plants' survival against Na and As. Proline biosynthesis supported in the maintenance of osmotic adjustment and plants sustained better activity through subdued electrolytic leakage. Oxidative stress due to both Na and As exposure is responsible for induction under significant moderation of lipid peroxidation and protein carbonization by 2,4-D application was evident to release the stress from metal and metalloids. Reactive oxygen species (ROS) like superoxide and hydrogen peroxide accumulation were monitored with activity of NADP(H)-oxidase. However, it was downregulated by 2,4-D to check the oxidative damages. Superoxide dismutase and peroxidases were significantly moderated to reduce the oxidative degradation for both metals with 2,4-D induction. Glutathione metabolism and recycling of ascorbate with monodehydroascorbate activity were other features to maintain the redox homeostasis for metal toxicity. At the molecular level, polymorphic variations of concern genes in redox cascades demarked significantly for those two metals and established the biomarker for those metals, respectively. As a whole, the biocompatibility of auxin herbicide in Salvinia may raise the possibility for auxin metabolism and thereby, the bioaccumulation to Na and As vis-à-vis tolerance for ecological safety is established.

Exploring quinclorac resistance mechanisms in Echinochloa crus-pavonis from China

BACKGROUND

Barnyardgrass (Echinochloa spp.) is a global weed in rice fields. Quinclorac is commonly used to control barnyardgrass. However, due to persistent use, quinclorac resistance has evolved. We obtained quinclorac-susceptible (QS) and -resistant (QR1, QR2) lines from the progeny of a single resistant E. crus-pavonis for a resistance mechanism study.

RESULTS

Line QR1 exhibited resistance to high quinclorac rates (up to 6400 g ha^-1 ), whereas line QR2 exhibited a resistance/susceptibility segregation ratio of 3:1 at the field or lower rates (400, 100 g ha^-1 ). Intriguingly, a lower level of ¹⁴ C-quinclorac metabolism and hence a higher level of ¹⁴ C-quinclorac translocation was observed in QR1 than QS plants. The basal expression levels of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) and ACC oxidase 2 (ACO2) genes did not differ significantly between the QR1 and QS lines. However, more expression of ACS and ACO genes was induced by quinclorac treatment in QS than in QR1. Basal levels of β-cyanoalanine synthase (β-CAS) gene expression were similar in QS and QR1 plants, but a greater level of down-regulation was detected in QS than in QR1 plants after quinclorac treatment.

CONCLUSION

These results indicate QR plants are less responsive to quinclorac than QS plants in terms of up-regulating quinclorac metabolism and ethylene synthesis. Resistance in this E. crus-pavonis line is likely controlled by a single major gene, involving possibly an alteration in auxin signal perception/transduction to the ethylene biosynthesis pathway. The β-CAS is unlikely to play a major role in quinclorac resistance in this particular population.

Synthetic auxin herbicides: finding the lock and key to weed resistance

Synthetic auxin herbicides are designed to mimic indole-3-acetic acid (IAA), an integral plant hormone affecting cell growth, development, and tropism. In this review, we explore target site genes in the auxin signaling pathway including SCF^TIR1/AFB, Aux/IAA, and ARFs that are confirmed or proposed mechanisms for weed resistance to synthetic auxin herbicides. Resistance to auxin herbicides by metabolism, either by enhanced cytochrome P450 detoxification or by loss of pro-herbicide activation, is a major non-target-site resistance pathway. We speculate about potential fitness costs of resistance due to effects of resistance-conferring mutations, provide insight into the role of polyploidy in synthetic auxin resistance evolution, and address the genetic resources available for weeds. This knowledge will be the key to unlock the long-standing questions as to which components of the auxin signaling pathway are most likely to have a role in resistance evolution. We propose that an ambitious research effort into synthetic auxin herbicide/target site interactions is needed to 1) explain why some synthetic auxin chemical families have activity on certain dicot plant families but not others and 2) fully elucidate target-site cross-resistance patterns among synthetic auxin chemical families to guide best practices for resistance management.

Potential molecular traits underlying environmental tolerance of Pavona decussata and Acropora pruinosa in Weizhou Island, northern South China Sea

Coral species display varying susceptibilities to biotic or abiotic stress. To address the causes underlying this phenomenon, we profiled the Symbiodiniaceae clade type, bacterial communities and coral transcriptome responses in Pavona decussata and Acropora pruinosa, two species displaying different environmental tolerances in the Weizhou Island. We found that C1 was the most dominant Symbiodiniaceae subclade, with no difference detected between A. pruinosa and P. decussata. Nevertheless, P. decussata exhibited higher microbial diversity and significantly different community structure compared with that of A. pruinosa. Transcriptome analysis revealed that coral genes with significantly high expression in P. decussata were mostly related to immune and stress-resistance responses, whereas, those with significantly low expression were metabolism-related. We postulate that the higher tolerance of P. decussata as compared with that of A. pruinosa is the result of several traits, such as higher microbial diversity, different dominant bacteria, higher immune and stress-resistant response, and lower metabolic rate.