Transgenic Plant -1

Transgenic Plant -1

Which strategy delays insect resistance development?

Resistance evolution to Bt toxins accelerated when transgenic crops grown continuously on large acreage without alternative hosts for susceptible insects. Homozygous resistant insects emerging from Bt fields mating with each other rapidly increase resistance allele frequency. Refuge strategy maintains pool of susceptible individuals by planting non-transgenic crop nearby or mixing seeds. Susceptible moths from refuge mate with rare resistant survivors from Bt field producing heterozygous offspring. High dose of toxin expressed in transgenic plants kills heterozygotes because resistance general

Ref: Gould Annu Rev Entomol 1998 refuge strategy; Tabashnik Annu Rev Entomol 2013 mixing; NCBI NBK131103 insect resistance management; EPA refuge guidance 2001.

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Vip proteins differ from Cry proteins because they are:

Cry proteins form parasporal crystals during sporulation, requiring solubilization at high pH and proteolytic activation. Vip proteins differ temporally and biochemically. Vip1, Vip2, Vip3 secreted during exponential vegetative growth into culture supernatant, not associated with spores. Vip3A, most agriculturally relevant, shares no sequence homology with Cry domains, presents unique tetrameric structure and binds distinct receptors including scavenger receptor class C and fibroblast growth factor receptor-like protein, triggering apoptosis pathway in addition to pore formation. Activity prim

Ref: Estruch PNAS 1996 Vip vegetative; Donovan 2001 Vip3 structure; Yu Appl Environ Microbiol 1997 differences; PubMed 8855281 vegetative insecticidal proteins.

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Chloroplast transformation reduces gene escape because:

Containment of transgenes via organelle transformation addresses environmental concerns about pollen mediated gene flow. In angiosperms like tobacco and Arabidopsis, plastid division during microsporogenesis excludes plastids from generative cell that forms two sperm cells, so mature pollen contains virtually no chloroplast genome. Consequently paternal transmission of plastid DNA extremely rare, estimated at less than 0.1 percent, while maternal transmission through ovule provides nearly 100 percent inheritance. When transgene integrated into plastome via homologous recombination at trnI-trnA

Ref: Heifetz Transgenic Res 2000 plastid absent pollen; Daniell Trends Genet 2002 containment; Maliga Annu Rev Plant Biol 2004 maternal; NCBI NBK153361.

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Worldwide maximum cultivated transgenic crop is:

International Service for Acquisition of Agri-biotech Applications annually reports global adoption of GM crops. Historical data from 1996 to 2023 demonstrates herbicide tolerance trait dominates both by trait type and crop species. Among crops, soybean engineered for glyphosate tolerance occupied largest area, reaching over 94 million hectares in 2019, accounting for about half of all GM hectarage. Drivers include high demand for protein meal for animal feed, suitability of herbicide tolerance for large-scale mechanized farming in United States, Brazil, Argentina, adoption of no-till practice

Ref: ISAAA Brief 55 2019 global status herbicide tolerant soybean dominant; James ISAAA 2014; NCBI NBK131103 statistics; https://www.isaaa.org/resources/publications/briefs/55/

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Trypsin inhibitor gene transferred to tobacco was sourced from:

Search for effective protease inhibitor for transgenic resistance identified cowpea trypsin inhibitor as potent candidate due to broad activity against lepidopteran gut proteases and stability in alkaline environment. Cowpea Vigna unguiculata seeds accumulate defense proteins to protect against storage pests. Gene CpTI encoding 80 amino acid inhibitor with two disulfide bridges isolated from developing seeds and placed under CaMV 35S promoter. Tobacco transformed with CpTI exhibited 2 to 5 percent soluble protein as inhibitor, reducing tryptic activity of Heliothis virescens midgut extracts an

Ref: Hilder Nature 1987 CpTI cowpea tobacco; Gatehouse Plant Mol Biol 1993 Vigna; NCBI NBK131103; PubMed 3033487 cowpea trypsin inhibitor source.

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Proteinase inhibitor genes provide resistance by:

Insect midgut proteases are essential for dietary protein digestion into amino acids required for growth and development. Many Lepidoptera rely predominantly on serine proteases trypsin, chymotrypsin, and elastase active at alkaline pH 10. Proteinase inhibitor genes from plants encode small disulfide-rich proteins that act as pseudo-substrates, tightly occupying enzyme active site forming stable enzyme-inhibitor complex with Ki in nanomolar range. Larvae ingesting inhibitor containing transgenic tissue cannot hydrolyze ingested protein, experience amino acid starvation, upregulate protease syn

Ref: Ryan Annu Rev Phytopathol 1990 inhibitors defense; Johnson PNAS 1989 trypsin; NCBI NBK21541; PubMed 1861469 proteinase inhibitor mode action.

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Atrazine resistance is mediated by:

Atrazine belongs to s-triazine class that binds plastoquinone binding niche of photosystem II D1 protein encoded by psbA, interrupting electron flow from QA to QB, generating singlet oxygen and lipid peroxidation causing chlorosis. While psbA Ser264 to Gly mutation confers resistance in weeds, crop tolerance in maize mediated differently via enhanced metabolic detoxification. Glutathione S-transferases especially Tau and Phi classes conjugate triazine chlorine with sulfhydryl group of reduced glutathione producing GS-atrazine conjugate that is transported to vacuole by ABC transporters and fur

Ref: Shimabukuro Plant Physiol 1970 GST atrazine; Kreuz Curr Opin Plant Biol 2006 GST mediated; NCBI NBK22365; PubMed 16495050.

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Sulfonyl urea resistance is due to mutation in:

Acetolactate synthase also called acetohydroxyacid synthase catalyzes first common step of branched-chain amino acid biosynthesis: condensation of two pyruvate molecules to acetolactate leading to valine and leucine, and condensation of pyruvate and 2-ketobutyrate to acetohydroxybutyrate leading to isoleucine. Sulfonylurea herbicides such as chlorsulfuron and tribenuron bind in substrate access channel of ALS, blocking access to catalytic site containing thiamine pyrophosphate. Resistance evolves via non-synonymous mutations in ALS gene altering herbicide binding pocket without abolishing cata

Ref: LaRossa Trends Biotech 1984 ALS mutation; Tranel Weed Sci 2002 ALS Pro197; NCBI NBK21601; PubMed 14769484 sulfonylurea resistance mechanism review.

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bar gene encodes:

Phosphinothricin acetyltransferase belongs to GCN5-related N-acetyltransferase superfamily capable of acetylating amino group of L-phosphinothricin using acetyl-CoA donor. Enzyme encoded by bar gene from Streptomyces hygroscopicus comprises 183 amino acids, small globular protein with conserved motif A for acetyl-CoA binding. Catalytic mechanism involves formation of ternary complex and transfer of acetyl moiety to amino group of PPT, generating herbicidally inactive N-acetyl-PPT that does not interact with glutamine synthetase active site. In transgenic plants, PAT activity rapidly detoxifies

Ref: Thompson EMBO J 1987 PAT acetylates PPT; Wehrmann Nat Biotechnol 1996 bar; NCBI NBK131103 bar encodes PAT; https://www.ncbi.nlm.nih.gov/books/NBK131103/

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Bialaphos resistance in plants is conferred by:

Bialaphos tripeptide herbicide consists of phosphinothricin plus two alanine residues. In plant tissue peptidases release active phosphinothricin, structural analog of glutamate that inhibits glutamine synthetase essential for assimilation of ammonia into glutamine. Inhibition causes ammonia accumulation, photosynthesis disruption, and rapid cell death. Bacterium Streptomyces hygroscopicus produces bialaphos and protects itself via bar gene encoding phosphinothricin acetyltransferase. Enzyme transfers acetyl group from acetyl-CoA to free amino group of phosphinothricin, producing N-acetyl phos

Ref: Murakami Mol Gen Genet 1986 bar Streptomyces; De Block EMBO J 1987 Basta resistance; NCBI NBK131103 bar function; PubMed 2884102.

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EPSPS gene used in Roundup Ready crops was obtained from:

Glyphosate tolerance technology relies on EPSPS variant showing high glyphosate insensitivity while retaining catalytic activity. Soil bacteria from glyphosate production plant waste in Louisiana screened for EPSPS activity in presence of herbicide identified Agrobacterium sp. strain CP4, now classified as Agrobacterium tumefaciens, harboring class II EPSPS naturally tolerant due to structural changes in active site reducing binding affinity. Gene cloned, sequenced, and fused to chloroplast transit peptide from petunia EPSPS and enhanced 35S promoter, introduced into crops via Agrobacterium me

Ref: Barry US Patent 5633435 CP4 EPSPS; Funke PNAS 2006 structure; NCBI NBK131103 Agrobacterium CP4; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1482475/

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Roundup Ready crops are resistant to:

Roundup Ready is brand name for transgenic crops tolerant to glyphosate based herbicide Roundup. Native crop EPSPS inhibited by glyphosate application, blocking aromatic amino acid synthesis. Incorporation of insensitive EPSPS variant allows continued pathway function despite spray, enabling post-emergence weed control without crop injury. Crops carrying cp4-epsps gene survive broadcast over-the-top application at commercial rates, simplifying weed management and facilitating conservation tillage reducing soil erosion. Soybean, cotton, maize, canola, alfalfa, and sugar beet versions deregulate

Ref: Dill GM Crops 2005 Roundup Ready; Funke PNAS 2006 CP4; NCBI NBK131103; ISAAA Pocket K 10 herbicide tolerance mechanism.

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