Chapter 14 – Plant Biotechnology. What is plant biotechnology? Manipulating plants and plant...
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Transcript of Chapter 14 – Plant Biotechnology. What is plant biotechnology? Manipulating plants and plant...
Chapter 14 – Plant Biotechnology
What is plant biotechnology?
Manipulating plants and plant parts for practical uses– Improved food crops
Higher yields Improved nutrition Environmental tolerances
– Improved production of valuable molecules
– Production of novel molecules
Biotechnology & agriculture
Terminology– Transgenic– GMO– GM crop
Biotechnology and modern agriculture
A brief history of crop improvement
Strategies to manipulate genomes– Selection of desirable traits (manipulating
population genetics)– Introducing new genetic traits to a genome
Hybridization technologies– Cross pollination– Plant tissue culture (protoplast fusion)
Gene transfer technologies– Genetic “transformation” (gene gun,
Agrobacterium tumefaciens)
– Create a new trait (directed evolution)
Crop domestication
Artificial selection since ~9,000 B.C.
Origins of crop domestication
Published by AAAS
K.-i. Tanno et al., Science 311, 1886 (2006)
Fig. 1. Modern examples of dehiscent wild einkorn wheat ear (A) and spikelet (B). Detail of spikelet with smooth wild abscission scar (C), indehiscent domestic ear (D),
and detail of spikelet with jagged break (E) are shown. The bar chart (F) gives relative frequencies of subfossil finds with the absolute figures.
Selection of desirable genetic traits
Genetic selection and crop domestication
Many selection strategies have been developed
Example: Mass selection
Limitations of selection Restricted to genetic traits
existing within the crop species Homozygosity and inbreeding
depression
Introducing new traits:Hybridization
Cross-pollination– Domesticated variety as
one parent– Related variety or species
with a desirable traits
Crop improvement, hybridization & gene pools
Cladograms depict evolutionary relationships
Closely related speciesvs.
Distantly related species
Backcrossing to introgress a desirable trait
Hybridization and selection necessary to retain desirable traits
Backcrossing
Donor parent (DP)(wild/res.-RR)
Recurrent parent (RP)(domest./sus.-rr)X
F1 hybrid50% DP; 50% RP
All RrX
Recurrent parent(domest./sus.-rr)
F2
25% DP; 75% RP1-Rr:1-rr
XRecurrent parent(domest./sus.-rr)
Which genotype should be used for the next cross?
Genetics of backcrossingGeneration Donor genes Recurrent
genes
Parent 100% 100%
F1 50% 50%
1st bc 25% 75%
2nd bc 12.5% 87.5%
3rd bc 6.25% 93.75%
4th bc 3.12% 96.88%
5th bc 1.56% 98.44%
6th bc 0.78% 99.22%
7th bc 0.78% 99.22%
The earliest technique utilized to
improve agricultural crops was
1. Cross pollination2. Selection3. Back crossing4. Hybridization
Backcrossing involves1. Self pollination2. Crossing a crop to be improved
repeatedly back to a related wild species containing a desirable trait
3. Crossing the hybrid offspring of a cross pollination repeatedly back to the domesticated parent
4. Both 1 and 25. All of these
Germplasm conservation Gene banks are repositories for
genetic traits– National Genetics Resources Progra
m– Consultative Group on International
Agricultural Research
Limitations of hybridization
Restricted to plants that can naturally hybridize– Crosses to closely related species
usually successful– Hybridization to distantly related
species usually problematic Little to no seed produced Hybrids recovered are often sterile
Genetic drag (linkage)
Breaching reproductive barriers for crop improvement
Plant tissue culture– Embryo rescue– Protoplast fusion– Micropropagation
Somatic embryos, Sitka spruce
Protoplast fusion for hybridization
Wide crosses can be accomplished via protoplast fusion and tissue culture
regeneration
Brassica juncea (Pbt) x Thlaspi caerulescens (Znt & Nit)
Breaching reproductive barriers for crop improvement:
Recombinant DNA technology & genetic engineeringRecombinant DNA technology & genetic engineering
Recombinant DNA technology and crop improvement
Allows utilization of every species Allows direct transfer of a single gene Requires a method of gene transfer into
plant cells Requires regenerable plant cells
– Totipotency of many plant cell types allows for regeneration of entire plants from single cells
Whole plants can be regenerated via cell and tissue culture
Somatic embryogenesis
callus
Plant transformation technologies
Genetic transformation – creating transgenic organisms– Agrobacterium– Gene gun– Gene transfer to protoplasts
Agrobacterium transformation
T-DNA of A.t. becomes integrated in a plant chromosome
T-DNA can be customized
Limitations of Agrobacterium transformation
Does not infect (most) monocots Different A.t. strains have
different levels of virulence in different plant species
Gene Gun (animation)
Invented by Cornell researcher, John Sanford
Electroporation of protoplasts
Polyethylene glycol mediated transformation of sugarbeet stomatal guard cell protoplasts
Why guard cell protoplasts?
Only totipotent cell type
Microinjection of protoplasts
Examples of crop improvement through genetic engineering
Engineered herbicide resistance– Glyphosate (RoundUp™) and
EPSP synthase
Shikimate pathway
EPSP(3-Phospho-5-enoylpyruvylshikimate)
Glyphosate
X