111. The term ‘co-suppression’ was coined by Richard Jorgensen to explain:
(1) Patchy flower colour in petunia.
(2) Resistance to viral infection in tobacco.
(3) Production of white flowers in Ipomea.
(4) Silencing of actin gene in C. elegans

Detailed Explanation:

Question:
The term ‘co-suppression’ was coined by Richard Jorgensen to explain:

✅ Correct Answer: (1) Patchy flower colour in petunia.

What is Co-Suppression?

The phenomenon of co-suppression was first identified by Richard Jorgensen in the 1990s while studying gene expression in plants. Co-suppression is a form of post-transcriptional gene silencing where the expression of a transgene can lead to the silencing of both the transgene and the corresponding endogenous gene. In simpler terms, when a plant expresses a transgene that is similar to its own gene, it can cause both genes to be turned off.

Co-Suppression in Petunias:

In his famous study on petunias, Jorgensen observed that when plants were engineered to overexpress a gene responsible for producing purple pigments (in the flower), the result was not just an increase in pigmentation. Instead, the plants developed patchy flowers with both normal and white (unpigmented) areas.

• The reason for this was co-suppression. The overexpression of the pigment gene led to a silencing of both the introduced transgene and the plant’s own endogenous pigment genes.

• This effect is gene-specific and can occur when there is a high degree of sequence similarity between the introduced gene and the host plant’s gene.

Other Possible Answers Explained:

• (2) Resistance to viral infection in tobacco: While this could be related to RNA interference (RNAi) or gene silencing, it is not directly related to co-suppression. Co-suppression primarily involves gene silencing due to sequence similarity, not viral resistance.

• (3) Production of white flowers in Ipomea: While white flowers could be a result of gene silencing, this specific case was not the focus of Jorgensen’s co-suppression studies.

• (4) Silencing of actin gene in C. elegans: Gene silencing mechanisms, such as RNA interference, are present in C. elegans, but this is not an example of co-suppression as defined by Jorgensen in his work with petunias.

Why Co-Suppression Matters:

• Co-suppression helps us understand how genetic regulation works in plants and has had important implications for genetic engineering and the development of transgenic crops.

• It also played a critical role in the discovery of RNA interference (RNAi), a revolutionary method for silencing genes, which has since been used in many areas of research.

Conclusion

Co-suppression is a fascinating phenomenon that was first identified in petunia flowers by Richard Jorgensen. This discovery has led to a deeper understanding of gene silencing in plants and has broader implications for genetic research and plant biotechnology.

✅ Correct Answer: (1) Patchy flower colour in petunia.