plants 2 Flashcards
Summary
Agrobacterium is used in biotechnology to introduce genes of interest for their expression in plants through the Ti plasmid.
Rhizobia and Frankia bacteria fix atmospheric nitrogen in root nodules.
PGPR are bacteria able to promote the plant growth due to different mechanisms.
Mycorrhizal are almost in every plant, they increase the nutrient uptake (mainly nitrogen and phosphorus) and get carbon compounds from the plants.
Lichens take place between an algae/cyanobacteria and a fungus (not a plant).
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Summary
Agrobacterium is used in biotechnology to
introduce genes of interest for their expression in plants through the Ti plasmid.
Summary
Rhizobia and Frankia bacteria
fix atmospheric nitrogen in root nodules.
Summary
PGPR are bacteria able to
promote the plant growth due to different mechanisms.
Summary
Mycorrhizal are almost in every plant, they
increase the nutrient uptake (mainly nitrogen and phosphorus) and get carbon compounds from the plants.
Summary
Lichens take place between
an algae/cyanobacteria and a fungus (not a plant).
Use of Agrobacterium (biotechnology)
Agrobacterium tumefaciens is the
3 points
- causative agent of Crown gall tumours. This occurs when the bacterium releases part of its Ti plasmid into the plant cell cytoplasm.
- T-DNA is integrated into the host chromosome.
- Crown galls are formed as consequence of transfer integration and expression of bacterial T-DNA genes in the plant. Natural genetic engineering process.
Use of Agrobacterium (biotechnology)
Ti-plasmid - independent replicating circular DNA molecule
3 important regions
1. T-DNA: 12-24 kb, section that is transferred to the plant.
Contains:
* left and right borders
* genes for biosynthesis:
- auxin
- cytokinin
- opine
- Virulence: genes responsible for T-DNA transfer: vir genes
- Opine catabolism: proteins involved in the uptake and metabolisms of opines.
Use of Agrobacterium (biotechnology)
How we obtain a transgenic plant? 7 Main steps:
- Plasmid removed from Agrobacterium
- Cut the plasmid and foreign DNA with the same restriction enzyme
- Insert foreign DNA into T-DNA region
- Insert the plasmid back into Agrobacterium
- Agrobacterium transfer the insert into plant cells
- The plant cells are grown in culture
- The plants carry and express the new gene.
Use of Agrobacterium (biotechnology)
Limitations of Ti-plasmid as a vector:
4 points
- Size: is quite large (200-800 kb), for a recombinant experiment, smaller vectors are preferred.
- Restriction enzyme sites: no unique RE sites.
- Phytohormones should be removed (Auxin and cytokinin).
- Opine synthesizing genes should be removed.
Use of Agrobacterium (biotechnology)
Applications:
- Resistance to herbicides: e.g. glutathione S-transferase in rice.
- Resistance to insect: genes for insecticidal protein production. e.g. cry
- Resistance to diseases
- Resistance to abiotic stress: genes for regulation of signals to support the drought stress.
- Improvement of quality
- Production of compounds: antibodies, vaccines, etc.
- Also applied in the transformation of fungi, algae…
Bacterial mutualism
Dinitrogen (N2)
- makes up 80% of the air and is a formed by a strong covalent bond. Not usable in that form for plants or animals.
- N2 -> NH4+
converted by diazotrophs
Bacterial mutualism
Rhizobia-legume symbiosis
- nitrogen fixing microbes in legumes
- nodules ( special structures in roots full of symbiotic bacteria.) on roots contain bacteria
- bacteria supply nitrogen to plant, plant supplies carbon to bacteria
- Rhizobia: collectively name of soil bacteria able to establish nitrogen-fixing symbiosis with legumes.
- Bacteroids: rhizobia bacteria in nodules which fix nitrogen, not able to live as free-living bacteria anymore.
Bacterial mutualism
Rhizobia-legume symbiosis
The enzyme responsible for nitrogen fixation is called
nitrogenase - it is inhibited by oxygen.
Bacterial mutualism
Rhizobia-legume symbiosis
Leghemoglobin:
4 points
- It is similar to hemoglobin in that it binds O2.
- It is synthesized co-operatively by both parties; globin by the plant and heme group by the bacterium.
- It maintains a strict control over the free oxygen, bound to unbound in the ratio of 10,000:1. This is sufficient oxygen for bacteria to respire, but too little to inhibit nitrogenase.
- Responsible for the red pigment in functioning nodules.
Bacterial mutualism
Rhizobia-legume symbiosis
Plants that have a symbiotic relationship with N2-fixing bacteria have
improved growth, pigmentation and development.
Bacterial mutualism
Frankia – actinorhizal plants symbiosis
- Frankia: Gram-positive actinobacteria able to fix nitrogen as free-living organisms or in symbiosis with a group of plants collectively named actinorhizal plants.
- Nitrogen fixation occurs thanks to nitrogenase in special structures called vesicles.
Bacterial mutualism
Frankia – actinorhizal plants symbiosis
Frankia–actinorhizal plants vs rhizobia-legume symbiosis
- Similarities
Bacteria fix N2
Plant gives C sources
Flavonoids
Molecular dialogue
- differences
Vesicles vs leghemoglobin
Nod genes
N2 fixation: free-living Frankia vs bacteroids in Rhizobia
PGPR: Plant growth promoting rhizobacteria
3 points
- Bacteria that colonize plant roots and promote plant growth.
- The promotion could be:
direct: hormone production, nitrogen fixation, improve uptake of nutrients, …
indirect: protection against disease, induce of plant systemic resistance, - Bigger plants
Healthier plants
Avoid chemical fertilisation
PGPR: Plant growth promoting rhizobacteria
The main test for PGPR abilities:
5 points
- Nitrogen fixation
- IAA production
(IAA= indol acetic acid) - ACC deaminase production
(ACC= 1-aminocyclopropane-1-carboxylate) - Siderophore production
- Phosphate solubilisation
Fungi mutualism
Mycorrhizas
5 points
- Fungi growing in association with plant roots, mutual benefit is obtained by both partners.
- Nearly every plant are associated to mycorrhizal fungi – these fungi are divided into a number of groups.
- Fungi gain carbon nutrients (sugars).
- Host plant showed an improved efficiency of nutrient uptake – particularly phosphorus and nitrogen.
- Play key roles in improving agriculture production and bioremediation of polluted soils.
Fungi mutualism
Mycorrhizas - Ectomycorrhizae
5 points
- Basidiomycota, Ascomycota
- Mainly associated with roots of trees and shrubs.
- Fungal mycelium envelops roots and forms a sheath (mantle) around them.
- Fungus scavenges scarce nitrogen and phosphorus, which is translocated into the plant
- Penetrate in roots but not in the root cells.
Fungi mutualism
Mycorrhizas - Arbuscular mycorrhiza
5 points
- Glomeromycota
- Have the longest fossil history of any fungi - appearing in the roots of the earliest rooted land plants (Ordovician period, 450 Mya).
- Mainly associated with herbaceous spp. and grasses although may be associated with roots of seedling trees.
- Penetrate in root cells forming arbuscles (nutrient exchange) - coralloid ingrowths into root cells-
- Presence of vesicles (storage structures)
Fungi mutualism
Lichens
5 points
- symbiotic association between fungi (normally Ascomycota) and algae or cyanobacteria.
- colonise substrates not amenable to most other organisms: rock, bark, man-made structures (e.g. asbestos roofs, statues etc.)-
- dominant cover species in Arctic tundra, on or just above the rocky shore tide-line and in some rocky deserts and lava flows.
- Host: fungus, gets carbon sources.
- Symbiont: alga/cyanobacteria, get nitrogen and/or phosphorus sources
