Viral resistance

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biotic resistance towards plant

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Viral resistance

  1. 1. Viral resistance
  2. 2. STRESS Abiotic Component Biotic Component Sunlight  Salt concentration  Drought conditions  Temperatures  Soil condition  Oxidative agents  Cold conditions  Metal toxicity   Virus  Fungal pathogens  Bacteria  Nematodes  Insects  Weed  Parasitic angiosperms
  3. 3. INFECTED LEAF Biotic Stress – viruses  Modes of virus resistances  Viral coat protein mediated  Antisense  Ribozymes  Satellite sequences  Non structural protein resistance  Gene silencing 
  4. 4. Coat protein mediated cross protection Ability of first virus to prevent the effect of second virus.  Sanford and Johnston (1985)  Powell – Abel et al.(1986)  Part of viral genome  Focused on codes of coat protein of TMV  Well studied + easily transformed by Agrobacterium tumefaciens . 
  5. 5. Cont…..  CP coding seq Engineered CP coding seq cassette vector (pMON316) * 35 CaMV promoter * NOS terminator signal  In agrobacterial cells  Tobacco leaf disc – kanamycin medium  Plant with TMV Notes:- 3:1 ratio, increased infection = late symptoms
  6. 6. Non structural protein mediated resistances Non structural “replicase” protein  54 kDa ORF of TMV – Golemboski et al. (1990)  Pinto et al. (1999) oped rice yellow mosaic virus resistant transgenic crop by replicase.  Eg. Tobacco, potato, tomato, soybean, rice, citrus , orange, maize – CP TMV, AMV and TRV. 
  7. 7. Cont….. Milton Zaitlin’s lab, cornell University , Golemboski et al, 1990 – gene of viral replicase.  Use tobacco – 3 terminal TMV 54 kDa used for encoding repilcase.  MacFarlene and Davies (1992) similar expt.  Not clear mechanism – not effective. 
  8. 8. Antisense RNAs A Complementary DNA strand of a gene can be inserted in reverse orientation this is referred as antisense gene.  mRNA by normal gene complementary to mRNA of antisense gene.  Hybridize  Block the specific gene expression.  Sanford and Johnston (1985).  Eg. Beta 1,3-glucanase was down regulated by antisense RNA in Tobacco + tolerance mosaic virus+ delayed spread+ reduced virus yield. 
  9. 9. Ribozymes Ribozymes are small RNA molecules – catalytic cleavage of target RNA  Block the replication of RNA.  But not effective . 
  10. 10. Movement proteins rapid spread of virus.  30kDa protein of TMV  32 kDa protein of brome mosaic virus  transgenic tobacco plant – mutated 30kDa of MP.  hence competes with TMV virus  Develop resistance  Malyashenko et al (1993) – has cDNA thermal mutant MP of TMV showed resistances at 33̇͘ but not at 24˚c. ˚c 
  11. 11. Satellite sequences  Small RNA molecules that are unable to multiple in host cell without helper virus.  Not in replication but affect diseases symptoms  cucumber mosaic virus cucumovirus (CMV) symptoms – reduced – carrying satellite  Transgenic tobacco and tomato plant with CMV satellites – china – (1990 - 1992)  not good- sever disease symptoms  Satellites mutates very fast  Recombination bt satellites – serious
  12. 12. Mechanism of post-transcriptional gene silencing (PTGS)
  13. 13. Gene silencing in transgenic plants It was firstly reported when introduction of additional chalcone synthase gene was transformed to petunia flower to intensify the voilet color of flower  Obtained flowers (transgenic lines) were both 1. intensed violet colered type- transgenesis worked 2. and white colored as well-Both native and transgenic chalcone synthase turned off  Stable integration and expression of transgene is required for commercial exploitation.  Expression of introduced gene can be abberant - GENE SILENCING!!! 
  14. 14. bhendi yellow vein mosaic virus – gene silening in varoius plant
  15. 15. References H.S Chawla, Introduction to plant Biotechnology(2002) oxford and IBH publishing co. pvt ltd.  U. Satayanaryana, Book of Biotechnology (2010) 6th ,Uppala author-publish interlinks. John barton, transgenic plants (1992), imperial college press. A.Slater, N.Scott and M.Fowler, Plant biotechnology (2003),oxford university press. Google images. 
  16. 16. THANK YOU

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