Isolation and functional characterization of a cotton ubiquitination-related promoter and 5'UTR that drives high levels of expression in root and flower tissues

Stabilized Double-Stranded RNA Strategy Improves Cotton Resistance to CBW (Anthonomus grandis)

Cotton is the most important crop for fiber production worldwide. However, the cotton boll weevil (CBW) is an insect pest that causes significant economic losses in infested areas. Current control methods are costly, inefficient, and environmentally hazardous. Herein, we generated transgenic cotton lines expressing double-stranded RNA (dsRNA) molecules to trigger RNA interference-mediated gene silencing in CBW. Thus, we targeted three essential genes coding for chitin synthase 2, vitellogenin, and ecdysis-triggering hormone receptor. The stability of expressed dsRNAs was improved by designing a structured RNA based on a viroid genome architecture. We transformed cotton embryos by inserting a promoter-driven expression cassette that overexpressed the dsRNA into flower buds. The transgenic cotton plants were characterized, and positive PCR transformed events were detected with an average heritability of 80%. Expression of dsRNAs was confirmed in floral buds by RT-qPCR, and the T₁ cotton plant generation was challenged with fertilized CBW females. After 30 days, data showed high mortality (around 70%) in oviposited yolks. In adult insects fed on transgenic lines, chitin synthase II and vitellogenin showed reduced expression in larvae and adults, respectively. Developmental delays and abnormalities were also observed in these individuals. Our data remark on the potential of transgenic cotton based on a viroid-structured dsRNA to control CBW.

Functional characterization of the pUceS8.3 promoter and its potential use for ectopic gene overexpression

The pUceS8.3 is a constitutive gene promoter with potential for ectopic and strong genes overexpression or active biomolecules in plant tissues attacked by pests, including nematode-induced giant cells or galls. Soybean (Glycine max) is one of the most important agricultural commodities worldwide and a major protein and oil source. Herein, we identified the soybean ubiquitin-conjugating (E2) enzyme gene (GmUBC4; Glyma.18G216000), which is significantly upregulated in response to Anticarsia gemmatalis attack and Meloidogyne incognita-induced galls during plant parasitism by plant nematode. The GmUBC4 promoter sequence and its different modules were functionally characterized in silico and in planta using transgenic Arabidopsis thaliana and G. max lines. Its full-length transcriptional regulatory region (promoter and 5´-UTR sequences, named pUceS8.3 promoter) was able to drive higher levels of uidA (β-glucuronidase) gene expression in different tissues of transgenic A. thaliana lines compared to its three shortened modules and the p35SdAMV promoter. Notably, higher β-glucuronidase (GUS) enzymatic activity was shown in M. incognita-induced giant cells when the full pUceS8.3 promoter drove the expression of this reporter gene. Furthermore, nematode-specific dsRNA molecules were successfully overexpressed under the control of the pUceS8.3 promoter in transgenic soybean lines. The RNAi gene construct used here was designed to post-transcriptionally downregulate the previously characterized pre-mRNA splicing factor genes from Heterodera glycines and M. incognita. A total of six transgenic soybean lines containing RNAi gene construct were selected for molecular characterization after infection with M. incognita pre-parasitic second-stage (ppJ2) nematodes. A strong reduction in the egg number produced by M. incognita after parasitism was observed in those transgenic soybean lines, ranging from 71 to 92% compared to wild-type control plants. The present data demonstrated that pUceS8.3 is a gene promoter capable of effectively driving dsRNA overexpression in nematode-induced giant cells of transgenic soybean lines and can be successfully applied as an important biotechnological asset to generate transgenic crops with improved resistance to root-knot nematodes as well as other pests.

Discovery and functional characterization of novel cotton promoters with potential application to pest control

pGhERF105 and pGhNc-HARBI1 promoters are highly responsive to CBW infestation and exhibit strong activity in vegetative and reproductive tissues, increasing their potential application in GM crop plants for pest control. The main challenge to cotton (Gossypium hirsutum) crop productivity is the constant attack of several pests, including the cotton boll weevil (CBW, Anthonomus grandis), which uses cotton floral buds for feeding and egg-laying. The endophytic nature of the early developmental stages of CBW makes conventional pesticide-based control poorly efficient. Most biotechnological assets used for pest control are based on Bacillus thurigiensis insecticidal Cry toxins or the silencing of insect-pest essential genes using RNA-interference technology. However, suitable plant promoter sequences are required to efficiently drive insecticidal molecules to the target plant tissue. This study selected the Ethylene Responsive Factor 105 (GhERF105) and Harbinger transposase-derived nuclease (GhNc-HARBI1) genes based on available transcriptome-wide data from cotton plants infested by CBW larvae. The GhERF105 and GhNc-HARBI1 genes showed induction kinetics from 2 to 96 h under CBW's infestation in cotton floral buds, uncovering the potential application of their promoters. Therefore, the promoter regions (1,500 base pairs) were assessed and characterized using Arabidopsis thaliana transgenic plants. The pGhERF105 and pGhNc-HARBI1 promoters showed strong activity in plant vegetative (leaves and roots) and reproductive (flowers and fruits) tissues, encompassing higher GUS transcriptional activity than the viral-constitutive Cauliflower Mosaic Virus 35S promoter (pCaMV35S). Notably, pGhERF105 and pGhNc-HARBI1 promoters demonstrated more efficiency in driving reporter genes in flowers than other previously characterized cotton flower-specific promoters. Overall, the present study provides a new set of cotton promoters suitable for biotechnological application in cotton plants for pest resistance.

Evolution of multiple target-site resistance mechanisms in individual plants of glyphosate-resistant Eleusine indica from China

BACKGROUND

Glyphosate has been used for weed control in South China in various situations for four decades, and most Eleusine indica populations are suspected to have evolved resistance to glyphosate. This research investigated underling target-site glyphosate resistance mechanisms in six field-collected, putative glyphosate-resistant (R) E. indica populations.

RESULTS

The six R E. indica populations were confirmed to be low (1.8 to 2.6-fold) to moderately (5.6- to 8.4-fold) resistant to glyphosate relative to the susceptible (S) population. Sixty-seven glyphosate-surviving plants from the six R populations were used to examine target-site resistance mechanisms. Target-site 5-enolpyruvylshikimate3-phosphate synthase (EPSPS) overexpression (OE) (plus further induction by glyphosate treatment) and gene copy number variation (CNV) occurred in 94% R plants, and among them, 16% had the P106A mutation and 49% had the heterozygous double TIPS (T102I + P106S) mutation (plus P381L). In addition, a low number of R plants (6%) only had the homologous TIPS (plus P381L) mutation. The (CT)6 insertion mutation in the EPSPS 5†-UTR always associates with EPSPS OE and CNV. Progeny plants possessing EPSPS OE/CNV (and P106A) displayed low level (up to 4.5-fold) glyphosate resistance. In contrast, plants homozygous for the TIPS mutation displayed higher (25-fold) resistance to glyphosate and followed by plants heterozygous for this mutation plus EPSPS OE/CNV (12-fold).

CONCLUSIONS

Target-site glyphosate resistance in E. indica populations from South China is common with prevalence of EPSPS OE/induction/CNV conferring low level resistance. Individual plants acquiring both the TIPS mutation and EPSPS OE/CNV are favored due to evolutionary advantages. The role of (CT)6 insertion mutation in EPSPS CNV is worth further investigation. © 2021 Society of Chemical Industry.

Insights obtained using different modules of the cotton uceA1.7 promoter

The structure of the cotton uceA1.7 promoter and its modules was analyzed; the potential of their key sequences has been confirmed in different tissues, proving to be a good candidate for the development of new biotechnological tools. Transcriptional promoters are among the primary genetic engineering elements used to control genes of interest (GOIs) associated with agronomic traits. Cotton uceA1.7 was previously characterized as a constitutive promoter with activity higher than that of the constitutive promoter from the Cauliflower mosaic virus (CaMV) 35S gene in various plant tissues. In this study, we generated Arabidopsis thaliana homozygous events stably overexpressing the gfp reporter gene driven by different modules of the uceA1.7 promoter. The expression level of the reporter gene in different plant tissues and the transcriptional stability of these modules was determined compared to its full-length promoter and the 35S promoter. The full-length uceA1.7 promoter exhibited higher activity in different plant tissues compared to the 35S promoter. Two modules of the promoter produced a low and unstable transcription level compared to the other promoters. The other two modules rich in cis-regulatory elements showed similar activity levels to full-length uceA1.7 and 35S promoters but were less stable. This result suggests the location of a minimal portion of the promoter that is required to initiate transcription properly (the core promoter). Additionally, the full-length uceA1.7 promoter containing the 5'-untranslated region (UTR) is essential for higher transcriptional stability in various plant tissues. These findings confirm the potential use of the full-length uceA1.7 promoter for the development of new biotechnological tools (NBTs) to achieve higher expression levels of GOIs in, for example, the root or flower bud for the efficient control of phytonematodes and pest-insects, respectively, in important crops.

Development of transgenic cotton (Narasimha) using triple gene Cry2Ab-Cry1F-Cry1Ac construct conferring resistance to lepidopteran pest

High-yielding Indian cotton varieties are not amenable for regeneration and transformation because they are recalcitrant in nature. In this work, we have developed Narasimha (NA1325) cotton variety by introducing three Cry genes driven by three different promoters conferring insect resistance. The meristematic region of embryo axis explants were infected and co-cultivated with Agrobacterium tumefacience (LBA4404) harbouring pMDC100 vector with three Cry gene cassettes (alpha-globulin : Cry2Ab, DECaMV35s : Cry1F and nodulin : Cry1Ac) with Npt II as a selectable marker gene. Out of 1010 embryo axes explants infected, 121 (T₀) regenerated under two rounds of kanamycin selectionmedium.About 2551T₁ seedswere collected from111T₀ plants and these seeds screened again with kanamycin at seedling stage. The transgenic plants were characterized by PCR, real time quantitative PCR, lateral flow strip protein assay and insect bioassay. Out of 145 kanamycin resistant plants (T₁), twelve showed amplification of all four transgenes: Npt II, Cry2Ab, Cry1F and Cry1Ac through PCR with expected amplicons as 395, 870, 840 and 618 bp, respectively. Further, lateral flow strip test revealed Cry1F and Cry1Ac proteins accumulated in 12 plants, whereas Cry2Ab protein was detected in eight only. The transcripts of all three Cry genes were accumulated significantly higher in transgenic plants at T₂ generation. The transgenic lines showed effective resistance againstHelicoverpa armigera and Spodoptera litura larvae. The T₂ line L-3 exhibited highest percentage of insect mortality, in which transcripts of all cry genes were accumulated higher than other plants. The transgenic cotton plants carrying triple Cry genes could be an excellent germplasmresource for the breeders for introgressions.

Alterations in the 5' untranslated region of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene influence EPSPS overexpression in glyphosate-resistant Eleusine indica

BACKGROUND

The herbicide glyphosate inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). Overexpression of the EPSPS gene is one of the molecular mechanisms conferring glyphosate resistance in weeds, but the transcriptional regulation of this gene is poorly understood. The EPSPS gene was found to be significantly up-regulated following glyphosate treatment in a glyphosate-resistant Eleusine indica population from southern China. To further investigate the regulation of EPSPS overexpression, the promoter of the EPSPS gene from this E. indica population was cloned and analyzed.

RESULTS

Two upstream regulatory sequences, Epro-S (862 bp) and Epro-R (877 bp), of EPSPS were obtained from glyphosate-susceptible (S) and -resistant (R) E. indica plants, respectively, by high-efficiency thermal asymmetric interlaced polymerase chain reaction (HiTAIL-PCR). The Epro-S and Epro-R sequences were 99% homologous, except for two insertions (3 and12 bp) in the R sequence. The 12-base insertion in the Epro-R sequence was located in the 5' untranslated region (UTR) pyrimidine nucleotide-rich (Py-rich) stretch element. Promoter activity tests showed that the 12-base insertion resulted in significant enhancement of Epro-R promoter activity, whereas the 3-base insertion had little effect on Epro-R promoter activity.

CONCLUSION

Alterations in the 5' UTR Py-rich stretch element of EPSPS are responsible for glyphosate-induced EPSPS overexpression. Thus, EPSPS transcriptional regulation confers glyphosate resistance in this E. indica population. © 2018 Society of Chemical Industry.

Transgenic cotton expressing Cry10Aa toxin confers high resistance to the cotton boll weevil

Genetically modified (GM) cotton plants that effectively control cotton boll weevil (CBW), which is the most destructive cotton insect pest in South America, are reported here for the first time. This work presents the successful development of a new GM cotton with high resistance to CBW conferred by Cry10Aa toxin, a protein encoded by entomopathogenic Bacillus thuringiensis (Bt) gene. The plant transformation vector harbouring cry10Aa gene driven by the cotton ubiquitination-related promoter uceA1.7 was introduced into a Brazilian cotton cultivar by biolistic transformation. Quantitative PCR (qPCR) assays revealed high transcription levels of cry10Aa in both T₀ GM cotton leaf and flower bud tissues. Southern blot and qPCR-based 2^-ΔΔCt analyses revealed that T₀ GM plants had either one or two transgene copies. Quantitative and qualitative analyses of Cry10Aa protein expression showed variable protein expression levels in both flower buds and leaves tissues of T₀ GM cotton plants, ranging from approximately 3.0 to 14.0 μg g^-1 fresh tissue. CBW susceptibility bioassays, performed by feeding adults and larvae with T₀ GM cotton leaves and flower buds, respectively, demonstrated a significant entomotoxic effect and a high level of CBW mortality (up to 100%). Molecular analysis revealed that transgene stability and entomotoxic effect to CBW were maintained in T₁ generation as the Cry10Aa toxin expression levels remained high in both tissues, ranging from 4.05 to 19.57 μg g^-1 fresh tissue, and the CBW mortality rate remained around 100%. In conclusion, these Cry10Aa GM cotton plants represent a great advance in the control of the devastating CBW insect pest and can substantially impact cotton agribusiness.

Transgenic Cotton Plants Expressing Cry1Ia12 Toxin Confer Resistance to Fall Armyworm (Spodoptera frugiperda) and Cotton Boll Weevil (Anthonomus grandis)

Gossypium hirsutum (commercial cooton) is one of the most economically important fibers sources and a commodity crop highly affected by insect pests and pathogens. Several transgenic approaches have been developed to improve cotton resistance to insect pests, through the transgenic expression of different factors, including Cry toxins, proteinase inhibitors, and toxic peptides, among others. In the present study, we developed transgenic cotton plants by fertilized floral buds injection (through the pollen-tube pathway technique) using an DNA expression cassette harboring the cry1Ia12 gene, driven by CaMV35S promoter. The T0 transgenic cotton plants were initially selected with kanamycin and posteriorly characterized by PCR and Southern blot experiments to confirm the genetic transformation. Western blot and ELISA assays indicated the transgenic cotton plants with higher Cry1Ia12 protein expression levels to be further tested in the control of two major G. hirsutum insect pests. Bioassays with T1 plants revealed the Cry1Ia12 protein toxicity on Spodoptera frugiperda larvae, as evidenced by mortality up to 40% and a significant delay in the development of the target insects compared to untransformed controls (up to 30-fold). Also, an important reduction of Anthonomus grandis emerging adults (up to 60%) was observed when the insect larvae were fed on T1 floral buds. All the larvae and adult insect survivors on the transgenic lines were weaker and significantly smaller compared to the non-transformed plants. Therefore, this study provides GM cotton plant with simultaneous resistance against the Lepidopteran (S. frugiperda), and the Coleopteran (A. grandis) insect orders, and all data suggested that the Cry1Ia12 toxin could effectively enhance the cotton transgenic plants resistance to both insect pests.

Promoter isolation and characterization of GhAO-like1, a Gossypium hirsutum gene similar to multicopper oxidases that is highly expressed in reproductive organs

Cotton is one of the most economically important cultivated crops. It is the major source of natural fiber for the textile industry and an important target for genetic modification for both biotic stress and herbicide tolerance. Therefore, the characterization of genes and regulatory regions that might be useful for genetic transformation is indispensable. The isolation and characterization of new regulatory regions is of great importance to drive transgene expression in genetically modified crops. One of the major drawbacks in cotton production is pest damage; therefore, the most promising, cost-effective, and sustainable method for pest control is the development of genetically resistant cotton lines. Considering this scenario, our group isolated and characterized the promoter region of a MCO (multicopper oxidase) from Gossypium hirsutum, named GhAO-like1 (ascorbate oxidase-like1). The quantitative expression, together with the in vivo characterization of the promoter region reveals that GhAO-like1 has a flower- and fruit-specific expression pattern. The GUS activity is mainly observed in stamens, as expected considering that the GhAO-like1 regulatory sequence is enriched in cis elements, which have been characterized as a target of reproductive tissue specific transcription factors. Both histological and quantitative analyses in Arabidopsis thaliana have confirmed flower (mainly in stamens) and fruit expression of GhAO-like1. In the present paper, we isolated and characterized both in silico and in vivo the promoter region of the GhAO-like1 gene. The regulatory region of GhAO-like1 might be useful to confer tissue-specific expression in genetically modified plants.