Non-Browning Gene-Edited Banana

A new genetically-engineered banana has been developed by UK scientists providing them a longer shelf-life and limiting browning of the fruit.

About the Genetically-Engineered Banana

Developed by: The GM Banana has been developed by the UK-based biotech company Tropic.
The company claims that the GM Banana remains fresh and yellow for 12 hours even after being peeled, and is also less likely to turn brown when bumped during harvesting and transportation.
Objective: To increase yield, extend shelf-life and improve natural disease resistance of bananas to diseases like Panama disease and Black Sigatoka disease.
Technology Used: Advanced gene editing technologies like CRISPR along with the Gene Silencing tool GEiGS (Gene Editing induced Gene Silencing) has been used to switch off specific genes to develop valuable

About Bananas

Genus: Bananas are an elongated, edible fruit (botanically a berry) of the genus Musa, of the family Musaceae.
Species: Modern edible varieties have evolved from the two species ie. Musa acuminata and Musa balbisiana and their natural hybrids.
Native: Banana evolved in the humid tropical regions of rainforest of South East .Asia with India as one of its centres of origin.
Cultivation: At present banana is being cultivated throughout the warm tropical regions of the world between 300 N and 300 S of the equator.
Producers: India and China are the largest producers of bananas in 2022 accounting for approximately 26% of total production.

Climatic Conditions for Growing Bananas

Temperature: Bananas require consistently warm temperatures ranging from 26°C to 30°C
- Strong, hot winds can damage leaves and cause dehydration.
Humidity: A minimum humidity of 50% is recommended for Bananas cultivation with ideal humidity between 75% and 85%.
Rainfall: Bananas typically requires around 2000 mm or more well-distributed rainfall/year.
Sunlight: Bananas need at least 8 hours of sunlight daily for optimal growth and fruit production.
Soil: Bananas prefer fertile, well-drained soils with good water-holding capacity and pH between 5.5 and 7.5 is ideal.
- They avoid very alkaline or poorly drained soils.

traits such as disease resistance and improved quality.
Method: The production of enzyme polyphenol oxidase (PPO) is disabled in the existing banana genes.
- This modification stalls the browning of the bananas while not stopping its ripening process.
Significance:
- Reduce Food Waste: The New Banana variety has the potential to significantly reduce food wastage by more than 25% with reduced browning and delayed ripening along the supply chain.
- CO2 Emissions: Non Browning banana variety can support a reduction in CO2 emissions equivalent to over 9 million tonnes in the banana export market alone accounting to removing 2 million passenger vehicles from the road each year.
Adoption:
- The Non-Browning Gene-Edited Banana has been cleared for Production in the Philippines
- GM Arctic Apples were approved for commercial sale in the US since 2017.
  - The same gene (PPO) was silenced in Arctic apples developed by Okanagan Specialty Fruits Inc.

About the Enzyme Polyphenol Oxidase (PPO)

Polyphenol oxidase (PPO) is a copper-containing enzyme widely found in plants, animals, fruits, bacteria, and fungi and plays a crucial role in enzymatic browning and defense mechanisms.

Browning of Bananas

Ripening Process: Bananas change colour during their ripening cycle from deep green when raw to a delicious yellow when ripe and edible to an unappetising brown at the end of its life cycle caused by a hormone called ethylene.
Ethylene Production: Bananas keep producing ethylene even after being harvested unlike other fruits like melons and citrus fruits.
- Ethylene contact due to bananas bruising during handling triggers the activity of a number of genes like the production of the enzyme polyphenol oxidase (PPO).
- Bruising leads to the production of higher quantities of ethylene, and thus speeds up the ripening and browning process.
Polyphenol Oxidase (PPO): The enzyme is responsible for the browning of bananas.
- PPO comes in contact with oxygen and breaks down the yellow pigment in bananas to a brown hue.
- Blocking the production of polyphenol oxidase has also been shown to work in tomatoes, melon, kiwifruits and mushrooms.

Functions:
- Enzymatic Browning: PPO is responsible for the enzymatic browning reaction, which occurs when plant tissues are damaged or stressed, leading to the formation of dark pigments.
- Defense Mechanism: The enzyme’s activity increases in response to stress or damage and thus is involved in defense against herbivores and pathogens.
- Oxidation of Phenolic Compounds: PPO catalyzes the oxidation of monophenols and o-diphenols to o-quinones in the presence of oxygen, which can then polymerize to form brown or black pigments like melanin.
Factors Affecting Polyphenol oxidase (PPO) activity: Factors below can affect the enzyme’s catalytic efficiency and the rate of enzymatic browning.
- Temperature: PPO activity is temperature-dependent, with different plant species exhibiting varying optimal temperatures, generally in the range of 30-50 °C.
  - Example: PPO activity in cocoa pulp and seed gradually decreased with increasing temperature, indicating that high temperatures are not favorable.
- pH: Deviations from the optimal pH can lead to PPO instability and reduced activity.
- Oxygen: PPO activity is dependent on the presence of oxygen, as it is a necessary co-factor for the enzyme’s catalytic reaction.
  - Example: Oxygen levels can affect the rate of enzymatic browning in fruits and vegetables.
- Microbial Activity: Microbial activity can also influence PPO activity, as some microorganisms can produce compounds that inhibit or stimulate PPO activity.
- Pre-harvest Conditions: Pre-harvest conditions, such as stress or nutrient deficiencies, can affect the expression and activity of PPO.
Industrial Application:
- Food Industry: PPO-catalyzed browning can be desirable, for example, in the production of prunes, dark raisins, black tea, and green coffee beans.
- Biosensors: PPO can be used as a biocatalyst in the development of biosensors for various applications to detect the presence of specific compounds, such as phenols, in various samples.
- Wastewater Treatment: PPO, particularly tyrosinase and laccase, can be used to treat industrial wastewater by removing phenols and can be used in bioremediation processes to remove pollutants from wastewater.
- Pharmaceutical and Cosmetic Industries: PPO has been employed as a biocatalyst in the pharmaceutical and cosmetic industries.

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