Cucumber Mosaic Virus and RNA Silencing

• 29 Apr 2025

Source: TH 

Why in News?  

A German research team has developed  "effective double-stranded Ribonucleic acid (dsRNA)," enriched with potent small interfering RNA (siRNA) to boost plant immunity against viruses like Cucumber Mosaic Virus (CMV). This method cut CMV viral load by up to 80%, outperforming conventional approaches. 

• The innovation uses RNA silencing, a natural plant defence, to precisely detect and suppress the virus. 

What is Cucumber Mosaic Virus? 

• About: CMV is one of the most common and globally prevalent plant viruses. It belongs to the genus Cucumovirus in the Bromoviridae family. 
  • It is known for its extremely wide host range, it affects over 1,200 plant species, including vegetables, cereals, ornamentals, and medicinal plants. 
• Symptoms: CMV causes yellow mottling (irregular, light spots or streaks on plant leaves) , distorted or mosaic-patterned leaves, and stunted growth. 
  • Symptoms are commonly seen not only in cucumbers but also in melons, bananas, pumpkins, and other garden plants. 
• Transmission: It is spread primarily through sap-sucking insects like aphids. Around 90 aphid species are capable of transmitting the virus, making containment difficult. 
  • Aphids, belonging to the superfamily Aphidoidea, are small, soft-bodied insects that use slender mouthparts to suck fluids from plant stems and leaves. 
• Impact on India: In India, CMV causes 25–30% yield losses in bananas and up to 70% infection in pumpkins, cucumbers, and melons. 
  • Infected plants show mosaic discoloration, stunted growth, and deformed fruits, with no known cure available for CMV.

Note:  According to the Food and Agriculture Organisation (FAO), plant pests and diseases destroy nearly 40% of the world’s annual crop, costing the world more than USD 220 billion. Of that, plant viruses alone contribute to over USD 30 billion in losses each year. 

What is RNA Silencing in Plants? 

• About: RNA silencing is a natural defense mechanism in plants that helps them fight off viruses.  
  • When a virus infects a plant, it introduces double-stranded RNA (dsRNA), which signals the plant's immune system to respond. 
• Working of RNA Silencing: When a virus infects a plant, the plant activates Dicer-like enzymes (DCLs). 
  • DCLs slice the dsRNA into small fragments called small interfering RNAs (siRNAs).  
    • These siRNAs guide the plant’s defense system to recognize and destroy the viral RNA, preventing the infection from spreading. 
• Limitations of RNA Silencing: Not all siRNAs generated by the plant are effective in fighting the virus. 
  • The CMV mutates rapidly, often evading the plant’s natural defense mechanism, making the process less reliable. 
• Human Developed RNA Silencing Technologies: 
  • Host-Induced Gene Silencing (HIGS): It genetically modifies plants to produce virus-fighting dsRNA, offering continuous protection.  
    • However, its use is limited by regulations, high costs, and potential viral resistance. 
  • Spray-Induced Gene Silencing (SIGS):  A flexible alternative where plants are treated with RNA sprays. It triggers the plant’s immune response without genetic modification.  
    • SIGS is cost-effective and eco-friendly, but its effectiveness is limited due to traditional dsRNA formulations producing a random mix of siRNAs, many of which fail to efficiently silence the virus.

UPSC Civil Services Examination, Previous Year Questions (PYQs)  

Prelims

Q. In the context of recent advances in human reproductive technology, “Pronuclear Transfer” is used for (2020)

(a) fertilization of egg in vitro by the donor sperm  

(b) genetic modification of sperm producing cells  

(c) development of stem cells into functional embryos  

(d) prevention of mitochondrial diseases in offspring  

Ans: (d)  

Q. What is Cas9 protein that is often mentioned in news? (2019)

(a) A molecular scissors used in targeted gene editing  

(b) A biosensor used in the accurate detection of pathogens in patients  

(c) A gene that makes plants pest-resistant  

(d) A herbicidal substance synthesised in genetically modified crops  

Ans: (a)  

Q. With reference to the recent developments in science, which one of the following statements is not correct?(2019)

(a) Functional chromosomes can be created by joining segments of DNA taken from cells of different species.  

(b) Pieces of artificial functional DNA can be created in laboratories.  

(c) A piece of DNA taken out from an animal cell can be made to replicate outside a living cell in a laboratory.  

(d) Cells taken out from plasma and animals can be made to undergo cell division in laboratory petri dishes.  

Ans: (a)