Objectives of applied plant physiology: Increase productivity via: • Enhanced efficiency or resistance • Reduce losses to pests, stress, weeds How do we increase yield despite marginal environments? • Traditional breeding; artificial selection • Hybrids (2 species or cultivars crossed; generally close relatives) • Induce mutations tissue culture mutations • Find unique genotypes; propagate Time intensive, but effective • GMOs; transgenic plants • Recombinant DNA technology • Tissue culture of transformed cells • Time and $$ intensive • Concerns by public (explored M)
What traits are we modifying? Herbicide resistance (so we can spray fields with herbicide and not kill the crop) Insect resistance (so we don’t spray pesticides, the plants make the toxins) Disease resistance Enhanced shelf life, oil or nutritional content (golden rice) • All of these are generally single gene traits Hyperaccumulators – clean pollution Stress tolerance to drought, heat, cold, salt, pollution N fixation, C4 PSN • Problem with these = multiple genes or they involve symbiotic interactions, which are harder to transform
Agrobacterium tumifaciens Crown gall disease – a bacterium • Widespread • enters plant via wounds • causes cancer-like tumors (crown gall disease) • can reduce productivity • Gall grows and divides (even if bacteria dies) • Gall tissues have high [CK] and [IAA] • Opines (unusual a.a.) made (C source) • Agrobacterium transfers its plasmid into plant’s DNA • Interkingdom horizontal DNA/gene transfer!
Lateral gene transfer by A. tumifaciens Tumor inducing = (Ti) plasmid: Vir genes activated in response to plant wound signals T-DNA (endonuclease) cuts host DNA and then inserts its genes into host DNA! Bacterial DNA w/ eukaryotic gene promoters code for: IAA, CK synthesis; causes cell proliferation = home for bacterium Modified amino acids; unique C and N source for bacterium Is this useful?
We can make transgenic plants: Remove aa and hormone synthesis genes; Keep endonuclease Gene added from another species; new trait (e.g. herbicide, pest resistance) Selectable marker added (usually antibiotic resistance gene or GFP) Plant cells (tissue discs) exposed to transformed Ti plasmid New gene(s) integrated into plant DNA Transformed individuals selected on antibiotic plates Whole plants regenerated w/ tissue culture
A. tumifaciens transformation: Only works well on dicots Most of the world’s crop plants are monocots How could we transform them?
Benefits and costs/objections Find diversity of opinions that relate to benefits and costs Find data on: • Benefits of transgenic crops. Include data. • Disadvantages/concerns about GM crops. Include data. • How transgenic organisms are regulated; who? • Effect on beneficial or non-target insects. Include data. • Crop to weed gene transfer • Selecting for resistant insects/pathogens • Consumer health • Impact on genetic diversity of crops • Is there is a reduction in herbicide or pesticide use w/ GMOs? • What are concerns among people in developing nations? • Colorado State University has a good, but dated website with links. http://cls.casa.colostate.edu/transgeniccrops/index.html