L15 Plant Biotech
一、Plant Biotechnology
Gene Modify
1. Herbicide (除草剂) Resistance
Plants compete with other plants for sunlight and nutrients. Many farmers use herbicides to eliminate weeds (undesired plants) from their fields.
Farmers that plant herbicide-tolerant crop plants use less herbicide, herbicides that are less toxic, and till (plow) less, saving soil and fuel.
Gene Flow Through Pollen
Gene flow through pollen movement has to be monitored and controlled
There have been confirmed cases of gene transfer from crops to weeds and vice versa.
- What consequences are expected from gene flow?
- How can gene flow be minimized?
- How can consequences be mitigated?
2. Cisgenics
Cisgenics: Genes from the same or closely-related species
Some traits can be modified by the introduction of a cisgene –a gene from the same or closely-related species
Advantages:
Avoids lengthy backcrossing process
Particularly useful for plants propagated vegetatively, such as potato or apple
Disadvantages:
Gene must exist in gene pool
3. Transgrafting 移植
Transgrafting:
A non-transgenic shoot can be grafted onto transgenic root, so the food products and pollen don’t carry the transgene
4. Some New Techs
Zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs) are proteins that can produce double-strand DNA breaks that when repaired introduce site-specific mutations or insertions
The clustered regularly interspaced short palindromic repeats (CRISPR) / CRISPR-associated (Cas) system uses RNAs to target nucleases to specific sites; when repaired, site-specific mutations or insertions are introduced
Comparison of nucleases
Natural nuclease classes:
(A) Restriction enzyme (shown as a dimer), with separate DNA binding and DNA cleavage domains (left) and with a single dual-function domain (right);
(B) homing endonuclease with an extended DNA binding domain;
(C) type II CRISPR-associated nuclease with a guiding crRNA (blue) and tracrRNA (red). (Bottom)
Synthetic nuclease classes:
(D) zinc finger nuclease dimer;
(E) transcription activator-like effector nuclease (TALEN) dimer with nuclease domains;
(F) triple-helix–forming oligonucleotides with a single-chain nuclease (shown as a dimer).
1. ZFNs and TALENs
ZFNs and TALENs can be programmed to cleave specific sites
ZFNs recognize three base pair sequences. A series of four linked ZFNs has a 12-bp binding specificity
TALENs recognize DNA via a series of 33 – 35 amino acid domains that each recognizes a single DNA basepair
The CRISPR / Cas system uses RNA for targeting: cheaper than proteins
2. TAL Effectors
3. Repair and Mutation
Repair of the resulting double-strand breaks causes mutations / insertions
Applications
1. β-carotene (β-胡萝卜素) (pro-vitamin A)
Many staple foods are poor sources of β-carotene so many people do not get adequate vitamin A in their diet
To increase beta-carotene levels in plants, you need more synthesis, more storage or less catabolism
二、Issues With GM Tech
Risk
Before release into the environment, GM crops are subject to riskassessment and risk-management measures to evaluate:
Risks to human health (including toxicity and allergenicity)
Risks of evolution of resistance in target pathogens or pests
Risks to non-target organisms
Risks from movement of transgenes
Pollen can move DNA between plants. To minimize this possibility, GM crops have to be grown prescribed distances away from closely related plants. Technological methods to reduce this risk are being developed.