Question

ted esch 4 Home 100 Rescue Check Answer Napoli et al. (1990) produced genetically-modified petunias by inserting numerous copies of the petunia CHS individual genomes CHS codes for a key enzyme in the synthesis of anthocyanin a pigment that produces light purple petals in wild type petunias. The investigators hypothesized that additional copies of CHS would increase expression of the yani producing a phenotype of dark purple petals. Unexpectedly, 42% of modified plants yielded petals that were white or white with patches of purple. Contrary to initial predictions, results showed that overexpression of CHS had silenced expression of CHS. Select the best explanation for how overexpression of CHS silences expression of CHS O CHS overexpression interferes with tRNA secondary structure formation, preventing amino acid incorporation into protein products by ribosomes. O CHS overexpression increases concentration of CHS mRNA in the cytosol, which activates an RNA-induced silencing complex that degrades mRNA or suppresses its translation CHS overexpression induces mutation in the promoter, which decreases template affinity for RNA polymerase and prevents transcription of CHS. CHS overexpression induces addition of 5' caps and 3'poly(A) tails to mRNA molecules, modifications which prevent ribosomes from binding to the mRNA OCHS overexpression causes formation of CHS introns, which interfere with translation by forming d e stranded molecules with tRNA molecules.

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Answer 1

Answer:

• CHS codes for a key enzyme in the synthesis of anthrocyanin pigment in petunias.
• Experimental insertion of CHS gene, instead of producing hyperpigmented flowers, results in petunia petals with white patches, due to possible silencing of CHS gene itself.
• The best explanation for how overexpression of CHS silence the expression of CHS -

B) : CHS overexpression cincrease concentration of CHS mRNA in the cytosol, which activates a RNA induce silencing complex, that degrades mRNA or supress its translation.

• The actual explanation has yet to be understood till now. Such behaviour has been seen in another flavonoid gene, dihydroflavonol 4-reductase (DFR) also.
• The mechanism of suppression may involve interference of RNA strands with the transcription process itself.
• The transcription process may be blocked by interaction of RNA with duplex DNA, resulting in a triple helix structure (Hogan and Cooney, 1989).
• Alternatively, interaction may occur with the DNA strands when they are separated during the transcription process.
• Or in formation of RNAi i.e. RNA induce silencing complex, that degrades mRNA or supress its translation.

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