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

Verified step by step guidance

1. Understand the context: The UG4 gene is expressed in both stem and leaf tissues, but deletion E specifically lowers expression in leaf tissue. This suggests that the deleted region contains a regulatory element important for UG4 expression in leaf tissue but not in stem tissue.
2. Recall the concept of tissue-specific gene regulation: Gene expression can be regulated by enhancers, silencers, or other regulatory elements that interact with transcription factors. These elements can be tissue-specific, meaning they are active only in certain cell types.
3. Hypothesize the role of the deleted region: Deletion E likely removes a leaf-specific enhancer or other regulatory sequence that is required for the activation of UG4 in leaf tissue. Enhancers are DNA sequences that bind transcription factors to increase gene expression in a specific context.
4. Explain why stem tissue is unaffected: The regulatory elements controlling UG4 expression in stem tissue are likely located in a different region of the upstream DNA or are independent of the region deleted in E. This means the transcription factors and enhancers required for stem-specific expression remain intact.
5. Conclude the reasoning: Deletion E lowers UG4 expression in leaf tissue because it removes a leaf-specific enhancer or regulatory element. However, stem tissue expression is unaffected because the regulatory elements for stem-specific expression are located elsewhere and are not impacted by deletion E.

Key Concepts

Gene Regulation

Gene regulation refers to the mechanisms that control the expression of genes, determining when and how much of a gene product is made. This can involve various elements such as promoters, enhancers, and silencers, which interact with transcription factors to modulate gene activity in different tissues or developmental stages.

Tissue-Specific Expression

Tissue-specific expression is the phenomenon where certain genes are expressed in specific tissues while remaining inactive in others. This is often regulated by the presence of unique transcription factors or regulatory elements that respond to the cellular environment, allowing for specialized functions in different parts of the organism.

Deletion Mutations

Deletion mutations involve the removal of a segment of DNA, which can affect gene expression by disrupting regulatory elements. In the context of the UG4 gene, the specific location of deletion E may remove critical regulatory sequences necessary for activating UG4 expression in leaf tissue, while leaving stem tissue unaffected due to different regulatory requirements.