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