33 public questions tagged with this topic.
Bacillus thuringiensis (Bt) toxin provides resistance to insect pests, reducing the need for chemical pesticides. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Zoology section), Chapter: Biology - Zoology portion covering relevant system and function.
Micropropagation is a tissue culture technique used to produce large numbers of genetically identical plants from a single tissue or ll. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Zoology section), Chapter: Structural Organisation in Animals and Frog, Topic: Tissues, skeletal and organ systems.
Sucrose provides the energy required for the growth and development of plant lls in tissue culture media. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Zoology section), Chapter: Structural Organisation in Animals and Frog, Topic: Tissues, skeletal and organ systems.
crtI gene deployed in Golden Rice was sourced from soil bacterium Erwinia uredovora strain now taxonomically reclassified as Pantoea ananatis, a Gram-negative enterobacterium inhabiting plant surfaces capable of synthesizing carotenoids as photoprotective pigments. Gene encodes 489 amino acid phytoene desaturase with FAD binding domain catalyzing sequential introduction of four double bonds into phytoene backbone converting 15-cis-phytoene via phytofluene, zeta-carotene, neurosporene to all-trans lycopene with concomitant isomerization, effectively replacing plant PDS, ZDS, CRTISO functions. Bacterial enzyme simplified metabolic engineering reducing transgene count from three to two, avoiding homology-dependent gene silencing observed when introducing multiple plant desaturases sharing conserved domains. Codon usage adjusted for plant expression and fused to transit peptide for amyloplast import. In bacteria crtI operates without membrane association in cytosol, whereas in plants localized to plastid membranes where lipophilic substrates partition. Its broad substrate specificity and lack of feedback regulation increase flux. Isolation from bacteria exemplifies utilization of microbial modules to bypass plant regulatory constraints in biofortification.
Ref: Sandmann Eur J Biochem 1994 crtI bacterial; NCBI Gene crtI Pantoea; Beyer PNAS 2000.
Original Golden Rice event employed phytoene synthase gene cloned from Narcissus pseudonarcissus, common daffodil, a monocot bulbous geophyte storing high carotenoid levels in chromoplasts of perianth flowers bright yellow. Daffodil psy cDNA was available, well characterized, and known to encode plastid-localized enzyme with high activity converting GGPP to phytoene. Its coding sequence fused to endosperm-specific glutelin promoter Gt1 and pea rbcS transit peptide sequence MSMA to direct import into plastids via Toc-Tic translocon machinery. Expression in rice endosperm complemented missing endogenous activity, initiating flux toward carotenoids. Later analysis of Golden Rice 1 showed psy transcript level limiting, with phytoene accumulation modest. Syngenta improved design replacing daffodil psy with Zea mays maize psy1 under same promoter, achieving 23-fold higher total carotenoids and preferential beta-carotene accumulation because maize enzyme better codon optimized for monocot translation, higher catalytic efficiency and association with metabolon channeling substrate. Daffodil origin highlights cross-species utility of orthologous enzymes from ornamental plants for cereal biofortification using conserved plastid pathways.
Ref: Ye et al. Science 2000 Daffodil psy; Paine et al. 2005 Maize psy improvement; Plant Physiol.
Development of Golden Rice elegantly reduced complex plant carotenoid desaturation steps to two transgenes. Phytoene synthase psy catalyzes committed head-to-head condensation of two geranylgeranyl diphosphate GGPP molecules to colorless 15-cis-phytoene, rate limiting step strongly regulated by light and feedback. Phytoene requires four desaturation steps and isomerization to become all-trans lycopene red pigment. Higher plants use phytoene desaturase, zeta-carotene desaturase, carotene isomerase ZDS, CRTISO separately. Bacterial crtI from Erwinia uredovora performs all reactions in single polypeptide with FAD cofactor, converting phytoene directly to lycopene via poly-cis intermediates. Combined psy plus crtI sufficient because endogenous rice endosperm possesses residual lycopene beta-cyclase and other downstream enzymes induced by product accumulation. Vectors used rice glutelin Gt1 promoter for endosperm specificity ensuring seed expression, CaMV 35S for crtI, and pea Rubisco small subunit transit peptide targeting to amyloplasts where isoprenoid precursor GGPP generated via MEP pathway. This two-gene strategy minimized gene silencing and transgene load while restoring entire pathway up to beta-carotene.
Ref: Beyer et al. J Nutr 2002 Golden Rice pathway; NCBI Metabolic pathway psy crtI mechanism.
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 primarily lepidopteran but distinct from Cry1 due to different receptor usage, effective against Cry resistant strains with cadherin mutations. Stability during purification differs. Classification as vegetative insecticidal proteins emphasizes secretion stage and novelty, supporting pyramiding of Cry plus Vip to provide two modes of action in transgenic corn Viptera and cotton. Recognition of vegetative origin underpins resistance management strategy extending durability of Bt technology beyond classical crystal proteins. Transgenic stack of Cry1Ab plus Vip3Aa demonstrates 99 percent control of Helicoverpa zea even in areas with Cry resistance, validating distinct mode of action concept. Regulatory assessment includes mammalian toxicity and allergenicity studies showing Vip3 rapidly degraded in gastric fluid. Hence vegetative insecticidal proteins complement Cry library for durable resistance.
Ref: Estruch PNAS 1996 Vip vegetative; Donovan 2001 Vip3 structure; Yu Appl Environ Microbiol 1997 differences; PubMed 8855281 vegetative insecticidal proteins.
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 practices conserving soil moisture. Bt cotton occupies second but substantially less area. Edible vaccines and Golden rice remain uncommercialized or limited. Economic analysis shows herbicide tolerant soybean reduced production costs and simplified weed management compared to conventional. Therefore statistical surveys consistently identify herbicide resistant soybean as most widely cultivated transgenic crop worldwide, illustrating market preference for input trait providing management convenience over output traits requiring consumer acceptance. Adoption data illustrates correlation between herbicide tolerance trait and conservation tillage practices reducing soil erosion and carbon emissions. Continued dominance of soybean indicates farmer preference for simplified weed management enabling timely planting over high-value specialty traits requiring niche markets and identity preservation systems.
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/
Suspension cultures differ from callus grown on agar by continuous agitation ensuring homogeneous nutrient and gas distribution and removal of growth inhibitors. Inoculation of friable callus fragments into Erlenmeyer flasks on orbital shaker at 110 rpm disperses cells, creates single cells and small aggregates suitable for growth kinetic measurements, mutant selection, and bioreactor scale-up. Uniform cell size allows precise biomass estimation by packed cell volume and dry weight, enabling process control for large-scale production of cells for biochemical studies, somatic embryogenesis, artificial seeds, and secondary metabolite extraction. Solid cultures limit diffusion and expansion. Pollination or germination assays require whole plants, not isolated cells. Therefore primary utility of cell suspension culture lies in generating large quantities of actively dividing, relatively synchronized plant cells under controlled conditions for industrial biotechnology and fundamental cell biology research applications. Growth curve analysis shows lag, exponential, linear, and stationary phases over 14-day period. Packed cell volume and fresh weight measurement monitor proliferation. Synchrony achieved by phosphate starvation or aphidicolin block. Applications include production of somatic embryos for artificial seed technology and isolation of secondary metabolites under elicitation, demonstrating versatility of liquid culture system for large-scale cell multiplication protocols.
Ref: Murashige & Skoog 1962 suspension; Street 1977 suspension methods; NCBI NBK26844 large scale; Phillips Plant Cell Culture 2010 bioreactor.
Agrobacterium plasmids determine disease phenotype. Ti plasmid, tumor-inducing, contains T-DNA with iaaM, iaaH, and ipt genes overproducing auxin and cytokinin, causing undifferentiated gall. Ri plasmid, root-inducing, carries TL and TR T-DNA regions in agropine strains; TL harbors rol cluster essential for hairy root syndrome and TR carries auxin genes and agropine synthesis. Virulence region mediates T-strand excision and transfer via type IV secretion. Upon integration, rol gene expression modifies host signaling, stimulating root proliferation rather than callus. Laboratory disarmed Ri vectors retain vir functions but delete oncogenes for transformation purposes. Naming convention Ri originates from root inducing ability, distinguishing it from Ti. Knowing plasmid identities enables selection of appropriate strain for either crown gall studies or hairy root induction, forming foundation of plant genetic engineering vector development history. Comparative genomics shows Ri plasmid TL-DNA size approximately 20 kb harboring rolA-D, while TR-DNA carries aux1, aux2 and opine synthase. Sequence analysis distinguishes agropine, mannopine, and cucumopine Ri types based on opine signature. Agrobacterium rhizogenes strain selection influences virulence and host range, critical for successful transformation of recalcitrant legumes and woody species requiring optimized co-cultivation conditions.
Ref: White & Nester J Bacteriol 1980 Ri structure; Nilsson & Olsson Physiol Plant 1997 rol; NCBI NBK21414 Ti vs Ri; https://www.ncbi.nlm.nih.gov/books/NBK21414/
Hairy root syndrome originates when wounded dicot tissue is invaded by soil bacterium carrying root inducing plasmid. Transfer of T-DNA segment harboring rolA, rolB, rolC, rolD loci plus opine synthesis genes into host chromosome rewires hormone balance. rolB encodes tyrosine phosphatase increasing auxin sensitivity, rolC cytokinin glucosidase adjusting growth, together triggering extensive adventitious root emergence directly from callus. Roots grow plagiotropically, highly branched, hormone independent, and genetically stable for decades. In contrast Agrobacterium tumefaciens produces crown gall tumors via cytokinin and auxin genes. Distinguishing pathogens is vital for biotechnology applications: rhizogenes-mediated transformation provides root-specific secondary metabolite factories exploited for alkaloid, ginsenoside, and flavonoid production. Therefore Agrobacterium rhizogenes is identified as causal agent inducing hairy root cultures used worldwide in metabolic engineering research. Mechanism includes virD2 mediated T-strand processing and integration via non-homologous end joining, expression of rol genes altering auxin signal transduction via tyrosine phosphatase activity. Resulting roots produce opines like agropine used by bacteria as carbon source. Cultures maintained on hormone-free medium for years retain biosynthetic capacity for root-specific metabolites, validating Agrobacterium rhizogenes as natural genetic engineer.
Ref: Chilton Nature 1982 Ri plasmid; Tepfer PNAS 1984 hairy root; NCBI NBK21344 rol genes; PubMed 17302573 hairy root review 2014.
Elicitors boost secondary metabolite production by mimicking biotic attack triggering plant innate defense signaling and activation of defence related enzymes. Biotic elicitors include fungal cell wall fragments chitin chitosan glucans yeast extract bacterial flagellin; abiotic include jasmonic acid methyl jasmonate salicylic acid heavy metals copper cadmium UV-C ozone. Perception by pattern recognition receptors triggers calcium influx cyclic nucleotide gated channels, production of reactive oxygen species via NADPH oxidase RBOH, activation of mitogen activated protein kinase cascades MPK3 MPK6 leading to jasmonate isoleucine synthesis. Jasmonate signals transcription factors MYB WRKY ORCA that bind promoters of phenylpropanoid pathway enzyme phenylalanine ammonia lyase PAL cinnamate 4 hydroxylase chalcone synthase CHS, and terpenoid pathway HMGR terpene synthase. Resulting phytoalexins alkaloids paclitaxel vincristine flavonoids accumulate up to tenfold. Commercial process employs two stage culture: biomass accumulation stage low elicitor high auxin, then production stage elicitor addition at late exponential phase to redirect carbon flux from primary to secondary metabolism without severe growth inhibition enabling industrial bioreactor harvesting.
Ref: Ramachandra & Ravishankar Plant Cell Rep 2002 elicitors; Nature Plants secondary metabolism.
