Transgenic Approach for Abiotic Stress Tolerance

Characteristics features of plant stress protein No.Stress ProteinInduction agentCharacteristics features 1HSP (heat shock protein) Mostly by high temperature stress, also by water stress, salt stress, low temperature stress, in some cases also by abscisic acid Classified aslow molecular weight HSPs and high molecular weight HSPs, highly conserved amino acid sequence, nucleotide sequence of the corresponding genes is also conserved, stress-inducible of hs genes governed by HSEs (heat shock elements), selected HSPs are shown to act as chaperons 2Osmotic stress proteins such as WSPs (water stress proteins) and SSPs (salt stress proteins) Mostly by low water availability and salt stress, also induced by ABA Varied molecular weights and cellular locations, these proteins are mostly the enzymes involved in diverse functions such as production of different osmolytes, protein degradation, signal transduction events, gene regulation and transport. Roles of some WSPs is not well defined (i.e. such as for dehydrins, late embryogenesis, abundant proteins)

Characteristics features of plant stress protein No.Stress ProteinInduction agentCharacteristics features 3ANPs (anaerobic proteins) Mostly by anaerobic stress (caused by flooding or submergence stress) Discovered initially in maize and later shown tin o be universally present, most of the ANPs have been shown to be the enzymes of the fermentative or the glycolytic pathway, most genes encoding ANPs contain. AREs (anaerobic response elements) in their promoters 4Cold stress proteins such as COR (cold- regulated proteins) Mostly by low temperature stress, also by osmotic, oxidative stress and ABA Conserved proteins of varied sizes and functions, most COR genes contain specific nucleotide sequence that stimulate transcription in response to low temperature

Stress Induced gene expression 1.Genes encoding proteins with known enzymatic or structural functions 2.Protein with as yet unknown functions 3.Regulatory protein

Single action gene Osmoprotectant genes: Proline, Gly/Bet, Sugar polyols Detoxifying genes: SOD, PX Late embryogenesis abundant genes: LEA Transporter genes: Aquapurin, Ion transporter Multifunctional genes for lipid biosynthesis:GPAT (glycerol-3-phosphate acyltransferase), FAD7 (Fatty acid desaturase) Heat shock genes: HS

Regulatory Genes Transcription factors genes CBF/DREB, ABF, HSF, bZIP, MYC/MYB Signal transduction genes a. Osmocensors (AtHK-1) b. Phospholipid cleaving enzymes (PLD) c. Second messengers (Ptd-OH, ROS) d. MAP kinases, Ca+ censor (SOS-3) e. Calcium –dependent protein kinases (CDPKs)

Abiotic stress tolerance 1.Increase cellular level of osmotically-active solute (proline, glycinebetaine, mannitol, trehalose, fructans) 2.Increase levels of osmolytes 3.It is mediated by a number of biochemical reactions /physiological processes (a multi genic trait) 4.It can be augmented by pyramiding different stress-responsive genes

Osmolyte and Compatible Solutes GeneProteinSourceCellular role(s) gpatGlycerol 3- phosphate acyltransferase Cucurbita maxima, Arabidopsis thaliana Fatty acid unsaturation mtlDMannitol 1- phosphate dehydrogenase Eschericia coliManitol biosynthesis sodSuperoxide dismutase Nicotiana plumbaginifolia Superoxide dismutase Bet-BBetaine aldehyde dehydrogenase Eschericia coliGlycinebetaine dismutase

GeneProteinSourceCellular role(s) Bet-ACholine dehydrogenase Eschericia coliGlycinebetaine dismutase p5csPyroline 5- carboxylase synthase V. aconitifoliaProline biosynthesis Sac-BLevan sucraseBaccilus subtilisFructan biosynthesis Hva-1LEA proteinHordeum vulgare - Tps-1Trehalose 6- phosphate synthase Arabidopsis thaliana Trehalose biosynthesis Osmolyte and Compatible Solutes

GeneProteinSourceCellular role(s) Cod-A/Cod-1/CoxCholine oxidaseArthrobacter globiformis Glycinebetaine biosynthesis afpAntifreeze protein (AFP) SyntheticInhibit ice growth and recrystallization Imt-1Myo-inositol-o- methyl transferase Messembryanthe mum crystallinum D-ononitol biosynthesis BADHBetaine dehydrogenase SpinachGlycinebetaine byosynthesis Osmolyte and Compatible Solutes

GeneProteinSourceCellular role(s) Ect-A, Ect-B, Ect-C L-2,4- diaminobutyric acetyltransferase L-2,4- diaminobutyric acid trans-aminase L-ectoine synthase Halomonas elongata Ectoyne Ots-A, Ots-BTrehalose-6-P synthase Trehalose-6-P phosphatase Eschericia coliTrehalose Osmolyte and Compatible Solutes

GeneProteinSourceCellular role(s) Pro-DHProline dehydrogena se Arabidopsi s thaliana Proline HAL-3FMN-binding protein Saccharo myces cerevisae Na+/K+ homeostas is Osmolyte and Compatible Solutes

GeneProteinSourceCellular role(s) AtNHX-1Vacuolar Na+/H+ antiporter Arabidopsis thaliana Na+ vacuolar sequestration AtSOS-1Plasma membrane Na+/H+ antiporter Arabidopsis thaliana Na+ extrusion AVP-1Vacuolar H+- pyrophosphatase Arabidopsis thaliana Vacuolar acidification HAL-1K+/Na+ transport regulation Saccharomyc es cerevisiae K+/Na+ homeostasis Ion Transporters and Ion Homeostasis

GeneProteinSourceCellular role(s) MnSODSuperoxide dismutase Saccharomyces cerevisiae Reduction of O2 content Gly-1GlyoxylaseBrassica junceaS-D- lactoylglutathion e TPX-2PeroxidaseNicotiana tabacum Change cell properties GST GPX Glutathione S- transferase Glutathione peroxidase Nicotiana tabacum ROS scavenging Redox Proteins

GeneProteinSourceCellular role(s) DREB-1ATranscription factor Arabidopsis thaliana Improved gene expression Cnb-1CalcineurinSaccharomyc es cerevisiae Improved Ca++ signaling OsCDPK-7Protein kinaseOryza sativaImproved gene expression Transcription and signal transduction factors

GeneProteinSourceCellular role(s) DnaKHeat shock protein A. halophytica Protein stabilization Apo-InvApoplastic yeast- derived invertase Saccharomyc es cerevisiae Sucrose synthesis Mischelineous

Perspective in Abiotic Stress Tolerance 1.Abiotic stress elicit multigenic responses within the plant cells. The tolerance to different abiotic stress is contributed by a range of different biochemical/physiological mechanism 2.Only a limited number of plant genes with a definite function have been identified, cloned and characterized 3.Changing levels of transcription factors can alter the levels of several genes at the same time 4.The transgenics raised far for enhancing tolerance to abiotic stress have been achieved through employing strong constitutive promoters, for driving expression of the transgenes. Promoters which are induced by different abiotic stress including high temperature stress, anaerobic stress, salt stress and water stress have poor strength of expression when compared to constitutively expression promoter