Jorgensen in 1986 working with petunias stumbled across RNAi. He inserted transgenic copies of chalcone synthase, a limiting enzyme in the synthesis of the flower's purple pigment, but instead of getting a very purple flower he got white flowers. Since it takes dsRNA to activate RNA machinery, how it was activated since two copies of the gene are not complementary, or are they actually?
Thanks.
Knowing actual copy numbers of transgenes can sometimes be difficult. It is also possible that transgene arrays (if formed) are not always head to tail. So, there are many ways complementary transcripts might be produced...
In the work that you mention the authors use the chalcone synthase with the promoter CaMV35S, a constitutive and strong promoter sequence, that sometimes could give rise to an excess of transcript that may interact with itself forming dsRNA structures and with its homologous (in this case that acts as a complementary) sequence for the WT chalcone synthase that trigger the RNA interference mechanism to give rise the white phenotype in petunia.
Regards,
1. The variable transgene expression levels (including gene silencing) has been linked to multiple molecular factors such as (1) high transcription levels from multiple unlinked transgenes (such as "co-suppression"), (2) the copy number and orientation (either in tandem or inverted) of linked transgenes in a locus, and (3) the characteristics of closely linked plant genetic material.
2. Your question is related to the 'co-suppression' phenomena mentioned by Aaron above.
3. Other gene silencing involved in double-stranded RNA (dsRNA) forming. Several processes can lead to production of dsRNA. Those processes include, for example, antisense transcription and transcription of inverted repeats (or transgenes) (see attached figure #1, 'a').
When doing genetic transformation, two copies of transgenes can land inside a single locus with an inverted fashion ("inverted repeats"). When transcription across these two inverted transgenes occurs, a double-stranded hairpin RNA can form (Figure #2) and triggers degradation of homologous mRNA, resulting in transgene silencing (a PTGS, post-transcriptional gene silencing).
- Badges
- Science topic
- Similar topics
- Biological Science
- Botany
- Plant Biology