#herbicide resistance

Transgenic Plant -1

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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Transgenic Plant -1

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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Transgenic Plant -1

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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Transgenic Plant -1

Superweeds may arise due to transfer of genes conferring:

Superweeds describe weedy populations that have acquired herbicide resistance via gene flow from cultivated crops, making control challenging. When transgenic crop expressing bar gene for glufosinate tolerance or cp4-epsps for glyphosate tolerance cross-pollinates with sexually compatible weed such as Brassica rapa, hybrid offspring inherit resistance allowing survival under herbicide application. Repeated selection in fields sprayed with same herbicide enriches resistant allele frequency, and backcrossing to weed parent restores weediness while retaining transgene. Documented cases include gl

Ref: Snow Am J Bot 1997 superweeds; Ellstrand Bioscience 2001; NCBI NBK131103; ISAAA superweed brief 2020; https://www.isaaa.org/

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Plant tissue culture 3

Herbicide-resistant somaclonal variants are detected by:

Herbicide resistance is a positive selectable trait best confirmed through functional challenge. Somaclonal populations contain rare cells with modified target enzymes such as glyphosate-insensitive EPSP synthase, acetylated phosphinothricin via PAT, or amplified glutathione S-transferases conferring detoxification. Plating callus or cell suspensions onto medium supplemented with discriminating concentration of respective herbicide imposes lethal pressure, killing wild-type cells by blocking aromatic amino acid synthesis or glutamine synthetase, causing ammonia toxicity. Only resistant clones

Ref: Chaleff & Raytbauer Science 1985 herbicide selection; PubMed 24254045 in vitro selection; NCBI NBK131103 selection systems; Bhojwani herbicide resistance screening.

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