Prions, Moulds & Embryo Rescue Explained

(a) Prions: Nature and Significance

Prions are misfolded proteins that have the ability to transmit their misfolded shape to normal versions of the same protein. Unlike bacteria, viruses, or fungi, prions do not contain nucleic acid (DNA or RNA). They are infectious agents composed solely of protein. The term "prion" was coined by Stanley B. Prusiner in 1982, who later received the Nobel Prize in Physiology or Medicine in 1997 for his discovery.

The normal, correctly folded protein (PrPc) is found in the brain and other tissues. However, when it misfolds into the prion form (PrPsc), it becomes resistant to degradation and accumulates, leading to neuronal damage. PrPsc acts as a template, converting more PrPc into PrPsc, initiating a chain reaction.

Diseases caused by prions include:

• Creutzfeldt-Jakob Disease (CJD): A rare, degenerative, fatal brain disorder in humans.
• Variant Creutzfeldt-Jakob Disease (vCJD): Linked to the consumption of beef from cattle infected with Bovine Spongiform Encephalopathy (BSE).
• Bovine Spongiform Encephalopathy (BSE): Commonly known as "mad cow disease," affects cattle.
• Scrapie: Affects sheep and goats.
• Kuru: A prion disease historically found among the Fore people of Papua New Guinea, transmitted through ritualistic cannibalism.

Why thorough understanding is needed:

• Lack of effective treatment: Prions are extremely resistant to conventional sterilization methods (heat, radiation, disinfectants). There are currently no effective cures for prion diseases.
• Long incubation periods: Symptoms can take years to develop, making early detection difficult.
• Diagnostic challenges: Diagnosing prion diseases can be challenging, requiring specialized tests.
• Public health concerns: The potential for zoonotic transmission (from animals to humans) necessitates stringent surveillance and control measures.

(b) Moulds: Bane and Boon

Moulds are filamentous fungi that play a significant role in ecosystems and human affairs. They reproduce through spores, which are easily dispersed by air, water, and insects. While often associated with spoilage and disease, moulds also have numerous beneficial applications.

Moulds as a Bane:

• Food spoilage: Moulds can cause significant economic losses by spoiling fruits, vegetables, bread, and other food products.
• Mycotoxins: Some moulds produce toxic secondary metabolites called mycotoxins, which can contaminate food and feed, posing health risks to humans and animals. Examples include aflatoxins (produced by Aspergillus species) and ochratoxins.
• Allergies and respiratory problems: Mould spores can trigger allergic reactions and asthma attacks in susceptible individuals.
• Structural damage: Moulds can grow on building materials, causing structural damage and releasing harmful volatile organic compounds (VOCs).

Moulds as a Boon:

• Food production: Certain moulds are used in the production of cheeses (e.g., Penicillium roqueforti in Roquefort cheese, Penicillium camemberti in Camembert cheese), soy sauce (Aspergillus oryzae), and tempeh.
• Antibiotics: The first antibiotic, penicillin, was discovered from the mould Penicillium notatum by Alexander Fleming in 1928.
• Organic acids: Moulds like Aspergillus niger are used in the industrial production of citric acid, gluconic acid, and other organic acids.
• Enzymes: Moulds are a source of various enzymes used in food processing, detergents, and other industries.
• Bioremediation: Some moulds can degrade pollutants, making them useful in bioremediation applications.

(c) Embryo Rescue Techniques

Embryo rescue is a technique used in plant breeding to overcome the incompatibility barriers in wide hybridization. When crossing distantly related plant species, the resulting hybrid embryos often fail to develop due to genetic and physiological incompatibilities. Embryo rescue involves the excision of the immature hybrid embryo from the developing seed and its subsequent culture in vitro on a nutrient-rich medium.

Steps involved in embryo rescue:

1. Hybridization: Perform a cross between two distantly related plant species.
2. Ovule/Seed Collection: Collect ovules or immature seeds at a specific stage of development (typically before embryo maturation).
3. Embryo Excision: Carefully dissect out the hybrid embryo from the ovule under sterile conditions.
4. In Vitro Culture: Culture the excised embryo on a suitable nutrient medium containing plant growth regulators (auxins and cytokinins) to induce callus formation and subsequent plantlet development.
5. Plantlet Regeneration: Regenerate plantlets from the callus and transfer them to soil for acclimatization and growth.

Relevance to Recombinants: Embryo rescue is particularly important in creating recombinant plants through genetic engineering. When introducing foreign genes into plants, the resulting transgenic embryos may exhibit developmental abnormalities. Embryo rescue allows for the recovery of these otherwise inviable embryos, enabling the production of stable transgenic lines.