Herbicides Chlorsulfuron Research Articles

An efficient sulfadiazine selection scheme for stable transformation in the model liverwort Marchantia polymorpha.

Plant macroevolutionary studies leverage the phylogenetic position of non-flowering model systems like the liverwort Marchantia polymorpha to investigate the origin and evolution of key plant processes. To date, most molecular genetic studies in Marchantia rely on hygromycin and/or chlorsulfuron herbicide resistance markers for the selection of stable transformants. Here, we used a sulfonamide-resistant dihydropteroate synthase (DHPS) gene to enable sulfadiazine-based transformation selection in M. polymorpha. We demonstrate the reliability of sulfadiazine selection on its own and in combination with existing hygromycin and chlorsulfuron selection schemes through transgene stacking experiments. The utility of this system is further demonstrated through confocal microscopy of a triple transgenic line carrying fluorescent proteins labelling the plasma membrane, cortical microtubules, and the nucleus. Collectively, our findings and resources broaden the capacity to genetically manipulate the increasingly popular model liverwort M. polymorpha.

Transgene-free genome editing of vegetatively propagated and perennial plant species in the T0 generation via a co-editing strategy.

Transgene-free plant genome editing in the T0 generation is highly desirable but challenging1,2. Here we achieved such a goal using a co-editing strategy via Agrobacterium-mediated transient expression of cytosine base editor to edit ALS encoding acetolactate synthase to confer herbicide chlorsulfuron resistance as a selection marker, Cas12a/CRISPR RNA for editing gene(s) of interest, and green fluorescent protein for selecting transgene-free transformants. The biallelic/homozygous transgene-free mutation rates for target genes among herbicide-resistant transformants ranged from 1.9% to 42.1% in tomato, tobacco, potato and citrus. This co-editing strategy is particularly useful for transgene-free genome editing of vegetatively propagated and perennial plant species in the T0 generation.

Base Editors for Citrus Gene Editing.

Base editors, such as adenine base editors (ABE) and cytosine base editors (CBE), provide alternatives for precise genome editing without generating double-strand breaks (DSBs), thus avoiding the risk of genome instability and unpredictable outcomes caused by DNA repair. Precise gene editing mediated by base editors in citrus has not been reported. Here, we have successfully adapted the ABE to edit the TATA box in the promoter region of the canker susceptibility gene LOB1 from TATA to CACA in grapefruit (Citrus paradise) and sweet orange (Citrus sinensis). TATA-edited plants are resistant to the canker pathogen Xanthomonas citri subsp. citri (Xcc). In addition, CBE was successfully used to edit the acetolactate synthase (ALS) gene in citrus. ALS-edited plants were resistant to the herbicide chlorsulfuron. Two ALS-edited plants did not show green fluorescence although the starting construct for transformation contains a GFP expression cassette. The Cas9 gene was undetectable in the herbicide-resistant citrus plants. This indicates that the ALS edited plants are transgene-free, representing the first transgene-free gene-edited citrus using the CRISPR technology. In summary, we have successfully adapted the base editors for precise citrus gene editing. The CBE base editor has been used to generate transgene-free citrus via transient expression.

Pesticide effects on nitrogen cycle related microbial functions and community composition

The extensive application of pesticides in agriculture raises concerns about their potential negative impact on soil microorganisms, being the key drivers of nutrient cycling. Most studies have investigated the effect of a single pesticide on a nutrient cycling in single soil type. We, for the first time, investigated the effect of 20 commercial pesticides with different mode of actions, applied at their recommended dose and five times their recommended dose, on nitrogen (N) microbial cycling in three different agricultural soils from southern Australian. Functional effects were determined by measuring soil enzymatic activities of β-1,4-N-acetyliglucosaminidase (NAG) and l-leucine aminopeptidase (LAP), potential nitrification (PN), and the abundance of functional genes involved in N cycling (amoA and nifH). Effects on nitrifiers diversity were determined with amplicon sequencing. Overall, the pesticides effect on N microbial cycling was dose-independent and soil specific. The fungicides flutriafol and azoxystrobin, the herbicide chlorsulfuron and the insecticide fipronil induced a significant reduction in PN and β-1,4-N-acetylglucosaminidase activity (P < 0.05) (NAG) in the alkaline loam soil with low organic carbon content i.e. a soil with properties which typically favors pesticide bioavailability and therefore potential toxicity. For the nitrifier community, the greatest pesticide effects were on the most dominant Nitrososphaeraceae (ammonia-oxidizing archaea; AOA) whose abundance increased significantly compared to the less dominant AOA and other nitrifiers. The inhibiting effects were more evident in the soil samples treated with fungicides. By testing multiple pesticides in a single study, our findings provide crucial information that can be used for pesticide hazard assessment.

A single gene inherited trait confers metabolic resistance to chlorsulfuron in grain sorghum (Sorghum bicolor).

This study confirms a high level of metabolic resistance to the herbicide chlorsulfuron, inherited by a single dominant gene in a sorghum genotype (GL-1). Chlorsulfuron, an acetolactate synthase (ALS)-inhibitor, effectively controls post-emergence grass and broadleaf weeds but is not registered for use in sorghum because of crop injury. The objectives of this study were to characterize the inheritance and mechanism of chlorsulfuron resistance in the sorghum genotype GL-1. Chlorsulfuron dose-response experiments were conducted using GL-1 along with BTx623 (susceptible check), and Pioneer 84G62 (commercial sorghum hybrid). The F1 and F2 progeny were generated by crossing GL-1 with BTx623. To assess if the target site alterations bestow resistance, the ALS gene, the molecular target of chlorsulfuron, was sequenced from GL-1. The role of cytochrome P450 (CYP) in metabolizing chlorsulfuron, using malathion, a CYP-inhibitor was tested. The chlorsulfuron dose-response assay indicated that GL-1 and F1 progeny were ~ 20-fold more resistant to chlorsulfuron relative to BTx623. The F2 progenies segregated 3:1 (resistance: susceptibility) suggesting that chlorsulfuron resistance in GL-1 is a single dominant trait. No mutations in the ALS gene were detected in the GL-1; however, a significant reduction in biomass accumulation was found in plants pre-treated with malathion indicating that metabolism of chlorsulfuron contributes to resistance in GL-1. Also, GL-1 is highly susceptible to other herbicides (e.g., mesotrione and tembotrione) compared to Pioneer 84G62, suggesting the existence of a negative cross-resistance in GL-1. Overall, these results confirm a high level of metabolic resistance to chlorsulfuron inherited by a single dominant gene in GL-1 sorghum. These results have potential for developing chlorsulfuron-tolerant sorghum hybrids, with the ability to improve post-emergence weed control.

Eco-Friendly Remediation of Adsorbed Chlorsulfuron Herbicide via Walnut Shells Derived Activated Carbon

Chlorsulfuron (1-(2-chlorophenyl) sulfonyl-3(4-methoxy-6-methyle-1,3,5-triazin-2-yl)) is the primary commercialized sulfonylurea weedicide aimed at combating several leafy weeds for the protection of many bowls of cereal and potato crops. It is used a pre as well as a post-emergent weedicide. Due to its organic ringed structure, it poses serious environmental degradation, particularly in the lithospheric compartment. The present investigation has analyzed its adsorptive interactions with soils inherently composed of unique physicochemical attributes. In a batch equilibrium experiment, sample 2 expressed the highest adsorption coefficient Kd(ads) with overall adsorption spanning over a range of 6.78 to 39.85 µg/mL. Adsorptive capacity analysis via Linear and Freundlich models yielded R2 > 0.8 indicative of best fitting of these models to Chlorsulfuron adsorption. Statistical analysis showed a negative correlation between soil pH and Kd(ads) (R2= -0.85) and a positive correlation with organic matter (R2= 0.96). The data was further analyzed by univariate ANOVA and its accuracy was checked through residual plots. Furthermore, the adsorbed Chlorsulfuron was remediated via the green method by utilization of walnut shells derived activated carbon in varying concentrations of 5 ppm and 7.5 ppm of Chlorsulfuron. The highest removal in 5 ppm was observed in soil 9 (85%) while in 7 ppm highest removal was observed in soil 2 (91%). Current investigation not only explored the adsorptive pattern of Chlorsulfuron but also developed a non-toxic, ecofriendly, pragmatic, and economical adsorbent for its removal.

Effects of sulfonylurea herbicides chlorsulfuron and sulfosulfuron on enzymatic activities and microbial communities in two agricultural soils.

Sulfonylurea herbicides are widely used for weed control in agriculture, and they are suspected to alter microbial communities and activities in the soil. This study investigates the impact of two sulfonylurea herbicides chlorsulfuron and sulfosulfuron on microbial community and activity in two different soils taken from two sites in west part of the Slovak Republic. The soil from the Malanta site was silt-loam luvisol with pH(H2O) 5.78 while the soil from the Stefanov site was sandy-loam regosol with pH(H2O) 8.25. These soils were not treated by sulfonylurea herbicides at least for 2years prior to the study. In laboratory assay, the herbicides were applied to soil in their maximal recommended doses 26 and 25g per hectare of chlorsulfuron and sulfosulfuron, respectively. Their effect was evaluated on the 3rd, 7th, 14th, 28th, 56th, and 112th day after application to soil. Illumina high-throughput amplicon sequencing of the 16S rRNA gene and ITS region was used to monitor changes on prokaryotic and fungal community composition. Enzymatic activity was evaluated using 11 substrates. Physiological profile of microbial community was analyzed using Biolog© ecoplates. Significant changes in enzymatic activity caused by the application of herbicides were found during the first 28days. The application of herbicides altered the activity of cellobiohydrolase, arylsulphatase, dehydrogenase, phosphatase, and FDA hydrolase. Chlorsulfuron caused a more varying response of enzymatic activity than sulfosulfuron, and observed changes were not the same for both soils. In Malanta soil, chlorsulfuron decreased dehydrogenase activity while it was increased in the Stefanov soil. Phosphatase activity was decreased in both soils on 7th and 14th day. There were only minor changes in prokaryotic or fungal community or physiological profiles regarding pesticide application. Differences between soils and incubation time explained most of the variability in these parameters. Diversity indices, physiological parameters, and enzymatic activity decreased over time. The results have shown that chlorsulfuron and sulfosulfuron can affect the function and activity of the soil microbial community without significant change in its composition.

Galium spurium and G. aparine Resistance to ALS-Inhibiting Herbicides in Northern Greece

ABSTRACT: Knowledge of the level of resistance of weed populations and the herbicides to which they survive is important for recommending suitable advice to farmers and allowing the selection of appropriate management strategies. Whole-plant dose response experiments were carried out to assess the resistance status of eight putative resistant Galium spurium L. populations and one G. aparine L. population, originating from northern Greece. High levels of resistance of both species to the ALS-inhibiting herbicides chlorsulfuron and tribenuron were found, while their susceptible populations were controlled. Three G. spurium (GS) populations showed additional cross-resistance to [florasulam + 2,4-D], whereas the remaining five resistant GS populations were controlled with [tribenuron + mecoprop-p], [florasulam + 2,4-D], and [florasulam + aminopyralid]. Also, [florasulam + fluroxypyr] was very effective against two resistant GS populations tested. DNA sequence alignment of the three GS populations (GS 1, GS 6, and GS 8) with cross-resistance to chlorsulfuron, tribenuron, and florasulam revealed a point mutation at Trp-574 (tryptophan-574), causing amino acid substitution by Leu (leucine). The G. aparine (GA) population showed cross-resistance to chlorsulfuron and tribenuron, but it was controlled with [tribenuron + mecoprop-p], [florasulam + aminopyralid], [florasulam + 2,4-D], and [florasulam + fluroxypyr]. The confirmed cross-resistance of both GS and GA species to chlorsulfuron and tribenuron in northern Greece is the first report of Galium spp. resistance to ALS-inhibiting herbicides in Europe. Finally, all populations (8 GS and 1 GA) that showed resistance to chlorsulfuron and tribenuron were controlled with the mixtures [tribenuron + mecoprop-p] and [florasulam + fluroxypyr].

Photocatalytic and Photoelectrochemically Degradation of Chlorsulfuron herbicide

Photocatalytic and photo electrochemical (PEC) degradation of chlorsulfuron herbicide were studied. Two novel PEC electrodes Ti/IrO2-Pt-WO3 (TIW) and Ti/IrO2-Pt-Ag3PO4 (TIA) were designed and some important factors were studied. Lower current density showed lower removal efficiency than higher conditions by electrochemical method. Furthermore, PEC showed higher degradation efficiency than the sum of individual EO and photocatalytic methode.

Research on controllable alkaline soil degradation of 5-substituted chlorsulfuron

Sulfonylurea (SU) has become one class of the most important herbicides worldwide due to their ultra-low application rate and mammalian toxicity. Recently application licenses of 3 classical SU herbicides chlorsulfuron, metsulfuron-methyl and ethametsulfuron were suspended due to their undesirable long persistence which is incompatible with the particular rotation planting system in China. Our previous study has discovered that electron-donating groups, especially dimethylamino and diethylamino substituents, on the 5th position of the benzene ring in chlorsulfuron, greatly accelerated its degradation rate in an acidic soil (pH 5.41). Owing to the natural slower degradation of SUs in alkaline soil, dimethylamino and diethylamino substituted chlorsulfuron Ia and Ib were further studied in an alkaline soil (pH 8.46) with chlorsulfuron as a control. The experimental data indicated that the half-life of degradation (DT50) of Ia was 3.36days while Ib was 6.25days which amounted to 30 and 15 folds faster than chlorsulfuron (DT50 84.53 days), respectively. The research confirmed that our newly-designed structures Ia and Ib can hasten their degradation rate in alkaline soil as well as in acidic soil. This structural modification of the classical SU provided an opportunity to control the degradation rate to reduce their impact on relevant environment and ecology.

Solid-phase modification of chitosan, pectin, and arabinogalactan with poorly soluble herbicide chlorsulfuron

The chemical modification of chitosan, pectin, and arabinogalactan with poorly soluble herbicide chlorsulfuron under mechanical effect is studied. It is shown that the mechanical stress on polysaccharides and herbicide provokes conformational and configurational transformations and disordering in biopolymer macromolecules as well as an increase in the concentration of defects in the crystalline phase of the polysaccharides and herbicide. The change in the conformational state of the polysaccharides under shock-shear impacts gives rise to intermolecular complexes stabilized by hydrogen bonds.

Inheritance of 2,4-D resistance traits in multiple herbicide- resistant Raphanus raphanistrum populations

A relatively low number of weed species have evolved resistance to auxinic herbicides despite their use for almost 70 years. This inheritance study with two Raphanus raphanistrum populations multiple-resistant 2,4-D and the ALS-inhibiting herbicide chlorsulfuron determined the number of genes and genetic dominance of 2,4-D resistance and investigated the association between traits conferring resistance to the two herbicide modes of action. Levels of 2,4-D phenotypic resistance and resistance segregation patterns were assessed in parental populations, F1 and F2 families.

Design, synthesis and herbicidal activity of novel sulfonylureas containing triazole and oxadiazole moieties

Three novel series of 5-substituted sulfonylurea derivatives were designed and synthesized via introducing a triazole or oxadiazole ring at the 5th position of the benzene ring in classical sulfonylurea herbicides. All the target compounds were confirmed by means of 1H nuclear magnetic resonance(NMR), 13C NMR and elemental analysis. The bioassay results show that the target compounds containing an oxadiazole ring at the 5th position display moderate to excellent herbicidal activities against Brassica campestris and Amaranthus retroflexus under soil treatment. Especially, compounds zdk20, zdk21 and zdk22 possess 98.6%, 96.5% and 94.5% inhibition rates, respectively, against Amaranthus retroflexus at a concentration of 75 g/ha(1 ha=1×104 m2) under soil treatment, which approach to those of the commercial herbicide chlorsulfuron.

English

The plasmids pULGU1 and pEmuGN were introduced by biolistics in embryogenic cell suspensions of pearl millet, Pennisetum glaucum . The plasmid pULGU1 contained the mutant acetolactate synthase (ALS) gene of Arabidopsis thaliana , responsible for resistance to the chlorsulfuron herbicide. The plasmid pEmuGN carried the reporter β-glucuronidase (GUS) gene of Escherichia coli . Two months after bombardment of the cells, transformed calli were selected on Murashige and Skoog medium containing 30 nM chlorsulfruron, a completely concentration inhibitory for non-transformed cells. A concentration of 200 nM chlorsufuron did not affect the growth of these selected resistant calli. Genomic DNA of resistant cells presented an electrophoretic pattern revealing the integration of the mutant ALS gene into the genome of Pennisetum glaucum . Expression of the GUS reporter gene was revealed by histochemical assay of the blue coloration of the calli in the presence of the substrate Xgluc (5-bromo-4-chloro-3-indolyl-β-D-Glucuronic acid). The presence of GUS gene was furthermore confirmed, by southern blot hybridization of non-radioactive probes, labelled with digoxigenin, on genomic DNA extracted from selected chlorsulfuron-resistant calli. GUS gene activity observed in all selected calli was high during the first 6 months after bombardment and then decreased. Pearl millet plants were regenerated from cell lines derived from chlorsulfuron resistant calli. Southern blot hybridization of non-radioactive probes with genomic DNA extracted from these regenerated plants showed the presence of the GUS and ALS transgenes, confirming the stable transformation of these plants. Key words : Pennisetum glaucum , stable transformation, chlorsulfuron (ALS), β-glucuronidase (GUS), CaMV35S and Emu promoters.

Changes in metabolites in maize seedlings under chlorsulfuron and cadmium stress

SUMMARYThe herbicide chlorsulfuron is commonly applied to cereals and may persist in alkaline soil long enough to damage subsequent sensitive crops. Sewage water, a potential source of the heavy metal cadmium (Cd), is used to irrigate agricultural soils in many developing countries. The current work evaluated the effects of the residual herbicide chlorsulfuron and Cd on maize seedlings, with particular attention to the mechanism of their action on plant growth. Maize seeds were planted in soil that had been sprayed with chlorsulfuron and Cd, after which residues in both seedlings and the soil were measured. The chlorsulfuron dose was correlated with the amount of residue found in seedlings but not in the soil. In all, 39 metabolites were identified in seedlings using the Automated Mass spectral Deconvolution and Identification System software program and the retention index method. The combination of chlorsulfuron and Cd significantly reduced multiple metabolites in the shikimate pathway, malic acid and citric acid production in the tricarboxylic acid cycle, and lactic acid, glucose, aspartic acid, asparagine and 3-glycerophosphoric acid production. In addition, chlorsulfuron caused an increase in multiple amino acids, including tyrosine, methionine and asparagine, and a marked decrease in caffeic and cinnamic acids (the secondary metabolites derived from the shikimate pathway and galactose). Finally, chlorsulfuron and Cd stress markedly increased shikimate acid, decreased 3-glycerophosphoric acid and caused negative correlations between the amounts of phenylalanine and tyrosine and those of quinic- and cinnamic-acid. In conclusion, chlorsulfuron and Cd did not have a synergistic effect on maize seedlings; rather, the combination of these pollutants had an antagonistic effect on some amino acids.

The influence of chlorsulfuron herbicide on GABA metabolism and oxidative damage in lentil (Lens culinaris Medik) and wheat (Triticum aestivum L.) seedlings

Abiotic stresses like salinity, drought, cold, heat, nutrient deficiency, and nutrient toxicity act as a major threats for crops quality and productivity. Herbicides are large category of chemical classes that affect various metabolic pathways and energy cascade in plants. γ-aminobutyric acid (GABA) is proposed to be critically involved in nitrogen metabolism, cytosolic pH regulation, and protection against oxidative imbalance in response to a wide range of abiotic stresses in plants. The objectives of this study were to determine the influence of chlorsulfuron herbicide on GABA metabolism and oxidative damage in two wheat (Triticumaestivum L.) cultivars (Hurani 75 and Um Qayes) and two lentil cultivars (Jordan 1 and Jordan 2) with respect to seed germination, GABA and malondialdehyde (MDA) levels accumulation, transcription of glutamate decarboxylase gene (GAD) mRNA level, total proteins, and carbohydrates contents. A significant increase in GABA, MDA and GAD mRNA level, proteins, and carbohydrates contents under chlorsulfuron treatments in the wheat and lentil cultivars was found in this study. The significant increase in GAD gene expression indicates the increase in GABA level under chlorsulfuron treatments. Hurani 75 and Jordan 2 cultivars showed significant decrease in protein level at high concentration of chlorsulfuron, whereas Um Qayes and Jordan 1 cultivars showed more tolerance under the same treatments. This study indicates that GABA metabolism might be one of multiple integrated signaling and metabolic pathways of herbicide stress adaptation and tolerance in wheat and lentil seedlings. This suggests that GABA molecule may act as a protective and metabolic signaling molecule in carbohydrates and proteins metabolism in plants under herbicidal treatments.

Kentucky Bluegrass and Perennial Ryegrass Mixtures for Establishing Midwest Lawns

Mixtures of turfgrass seed are commonly used to establish lawns, with kentucky bluegrass (KBG) and perennial ryegrass (PRG) comprising two of the more commonly used species. In the humid regions of the Midwest United States, KBG is a desirable species, but slow germination makes it difficult to establish compared with PRG. The objective of our study was to evaluate establishment rate and species composition over 3 years of a turf stand seeded with different ratios of KBG and PRG (wt:wt) maintained as a lawn. Repeat experiments were initiated in 2007 and 2008 and conducted for 3 years in West Lafayette, IN, with seed mixtures of KBG:PRG of 100:0, 90:10, 80:20, 70:30, 50:50, and 0:100 wt:wt of pure live seed. Plots were seeded late August each year and percent turfgrass cover was rated up to 6 weeks after seeding (WAS). To evaluate stand composition after establishment, percent KBG cover was rated annually in August for 3 years using transect counts after selective removal of PRG with the herbicide chlorsulfuron. Likely as a result of greater crabgrass (Digiaria sp.) competition during establishment in 2007, 100% PRG, 50:50, 70:30, or 80:20 KBG:PRG ratio had the highest percentage turf cover at 6 WAS, whereas there was no difference between treatments at 6 WAS in 2008 when crabgrass competition was lower. Regardless of turf cover during establishment, all treatments except 100% PRG shifted to greater than 95% KBG cover by 3 years after establishment. For the region in which our study was conducted, it may be desirable to seed with a higher proportion (greater than 50%) of PRG to speed initial establishment for customer satisfaction, erosion control, and/or to offset years with high weed pressure. Under lawn conditions similar to our study, seeding ratios with high KBG (80:20 or 90:10 KBG:PRG) will likely shift to a stand composition of greater than 95% KBG within 2 years, whereas all other ratios lower in KBG will likely shift similarly within 3 years. Chemical names used: 2-chloro-N-{[(4-methoxy-6-methyl-1,3,5-triazin-2 yl)amino]carbonyl}benzenesulfonamide (chlorsulfuron)

Multiple herbicide-resistant wild radish (Raphanus raphanistrum) populations dominate Western Australian cropping fields

Raphanus raphanistrum is a problematic weed, which has become increasingly difficult to control in Australian cropping regions. In 2010, a random survey was conducted across 14 million ha of the Western Australian grain belt to establish the frequency of herbicide resistance in R. raphanistrum and to monitor the change in resistance levels by comparing results with a previous survey in 2003. Screening R. raphanistrum populations with herbicides commonly used to control this weed revealed that most populations (84%) contained individual plants resistant to the acetolactate synthase-inhibiting herbicide chlorsulfuron, whereas 49% of populations also had plants resistant to the imidazolinone herbicides. Resistance to other mode of action herbicides (2,4-D (76%) and diflufenican (49%)) was also common. Glyphosate, atrazine and pyrasulfotole + bromoxynil remained effective on most R. raphanistrum populations. These results demonstrate that resistance to some herbicides has increased significantly since 2003 when the values were 54% for chlorsulfuron and 60% for 2,4-D; therefore, a wide range of weed management options that target all phases of the cropping program are needed to sustain these cropping systems in the future.

Genetic inheritance of cytochrome P450-mediated metabolic resistance to chlorsulfuron in a multiple herbicide resistant Lolium rigidum population

Field evolved resistance to acetolactate synthase (ALS)-inhibiting herbicides in a multiple resistant Lolium rigidum population (VLR69) is known to be mainly due to enhanced rates of herbicide metabolism, likely involving cytochrome P450 monooxygenases. The present study investigates genetic inheritance of P450-mediated metabolic resistance to the ALS-inhibiting herbicide chlorsulfuron. To this end, a P450-mediated, metabolism-based resistant sub-set of VLR69 was carefully selected using plant vegetative cloning, appropriate herbicide screen test and the known P450 inhibitor malathion. Both intermediate and near-dominant nuclear-encoded phenotypic resistance traits were observed in 14 reciprocal F1 families. The segregation of phenotypic chlorsulfuron resistance in ψ-F2 families was analysed using genetic inheritance models involving one or two loci. The results from four ψ-F2 families revealed complex patterns of genetic inheritance of P450-mediated metabolic resistance in genetically diverse and cross-pollinated species L. rigidum: multiple loci are likely involved and interact with herbicide rates and environmental conditions in mediating the resistance phenotype.

Down-regulation of acetolactate synthase compromises Ol-1- mediated resistance to powdery mildew in tomato.

BackgroundIn a cDNA-AFLP analysis comparing transcript levels between powdery mildew (Oidium neolycopersici)-susceptible tomato cultivar Moneymaker (MM) and near isogenic lines (NILs) carrying resistance gene Ol-1 or Ol-4, a transcript-derived fragment (TDF) M11E69-195 was found to be present in NIL-Ol-1 but absent in MM and NIL-Ol-4. This TDF shows homology to acetolactate synthase (ALS). ALS is a key enzyme in the biosynthesis of branched-chain amino acids valine, leucine and isoleucine, and it is also a target of commercial herbicides.ResultsThree ALS homologs ALS1, ALS2, ALS3 were identified in the tomato genome sequence. ALS1 and ALS2 show high similarity, whereas ALS3 is more divergent. Transient silencing of both ALS1 and ALS2 in NIL-Ol-1 by virus-induced gene silencing (VIGS) resulted in chlorotic leaf areas that showed increased susceptibility to O. neolycopersici (On). VIGS results were confirmed by stable transformation of NIL-Ol-1 using an RNAi construct targeting both ALS1 and ALS2. In contrast, silencing of the three ALS genes individually by RNAi constructs did not compromise the resistance of NIL-Ol-1. Application of the herbicide chlorsulfuron to NIL-Ol-1 mimicked the VIGS phenotype and caused loss of its resistance to On. Susceptible MM and On-resistant line NIL-Ol-4 carrying a nucleotide binding site and leucine rich repeat (NB-LRR) resistance gene were also treated with chlorsulfuron. Neither the susceptibility of MM nor the resistance of NIL-Ol-4 was affected.ConclusionsALS is neither involved in basal defense, nor in resistance conferred by NB-LRR type resistance genes. Instead, it is specifically involved in Ol-1-mediated resistance to tomato powdery mildew, suggesting that ALS-induced change in amino acid homeostasis is important for resistance conferred by Ol-1.