The UG4 gene is expressed in stem tissue and leaf tissue of the plant Arabidopsi

Question

The UG4 gene is expressed in stem tissue and leaf tissue of the plant Arabidopsis thaliana. To study mechanisms regulating UG4 expression, six small deletions of DNA sequence upstream of the gene-coding sequence are made. The locations of deletions and their effect on UG4 expression are shown below.

Part A

Explain the differential effects of deletions B and F on expression in the two tissues.

Select all that apply.

F. The deletion in mutant F has no effect on UG4 expression in either tissue, indicating that this region contains no sequences important for transcription whatsoever.

Part C

Why does deletion E lower expression of UG4 in leaf tissue but not in stem tissue?

A. Mutant B only mildly affects UG4 transcription in leaves, but knocks it out almost entirely in stems. This indicates the use of different promoter sequences in the transcription of UG4 in these tissues. B. The deletion in mutant F has no effect on UG4 expression in either tissue, indicating that this region contains no sequences required for promoter action in those cells. C. Mutant B only mildly affects UG4 transcription in leaves, but knocks it out almost entirely in stems. This indicates the use of different homologous chromosomes in these tissues. D. Mutant B only mildly affects UG4 transcription in leaves, but knocks it out almost entirely in stems. This indicates the use of different transcription factors in these tissues. E. The deletion in mutant F has no effect on UG4 expression in either tissue, indicating that this region contains sequences which downregulate transcription in those cells.

F. The deletion in mutant F has no effect on UG4 expression in either tissue, indicating that this region contains no sequences important for transcription whatsoever.

Part C

Why does deletion E lower expression of UG4 in leaf tissue but not in stem tissue?

A. Mutations in regions at a distance from the transcription start site that prevent expression typically affect a silencer; therefore, mutation E deletes a required silencer sequence for UG4 transcription in leaf tissue but not in stem tissue. B. Mutations in regions close to the transcription start site that prevent expression typically affect the start codon; therefore, mutation E deletes a required start codon sequence for UG4 transcription in leaf tissue but not in stem tissue. C. Mutations in regions close to the transcription start site that prevent expression typically affect a promoter; therefore, mutation E deletes a required promoter sequence for UG4 transcription in leaf tissue but not in stem tissue. D. Mutations in regions at a distance from the transcription start site that prevent expression typically affect an enhancer; therefore, mutation E deletes a required enhancer sequence for UG4 transcription in leaf tissue but not in stem tissue. Transcription Promoter start Upstream region region UG4 gene Deletion E D A C regions Transcription (96) Stem Leaf Deletion None (control) 100 100 100 100 1 9 100 100 100 163 98

Explanation / Answer

Part A

Mutant B only mildly affects UG4 transcription in leaves, but knocks it out almost entirely in stems. This indicates the use of different promoter sequences in the transcription of UG4 in these tissues. Also, the deletion in mutant F has no effect on UG4 expression in either tissue, indicating that this region contains no sequences required for promoter action in those cells.So, the correct options are option A and B.

Part C

Deletion E lowers expression of UG4 in leaf tissue but not in stem tissue. It is because mutations in regions at a distance from the transcription start site that prevent expression typically affect an enhancer; therefore, mutation E deletes a required enhancer sequence for UG4 transcription in leaf tissue but not in stem tissue. So, the correct option is option D.

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