The homeotic gene GLABRA-2 controls cellular differentiation in the root epidermis of Arabidopsis. Which of the following statements is/are correct?

• A. If GLABRA-2 is expressed, the cell produces a root hair.
• B. If an epidermal cell borders one cortical cell, GLABRA-2 is expressed, and the cell produces a root hair.
• C. If GLABRA-2 is not expressed, no root hairs are formed.
• D. The first and second responses are correct.
• E. If an epidermal cell borders two cortical cells, GLABRA-2 is not expressed, and the cell produces a root hair.

Answer: (E)

Verified step by step guidance

1. Understand the role of the GLABRA-2 gene: It is a homeotic gene involved in the differentiation of root epidermal cells in Arabidopsis, specifically influencing the formation of root hairs.
2. Identify the conditions under which GLABRA-2 is expressed: Typically, GLABRA-2 is expressed in epidermal cells that do not form root hairs. This means that when GLABRA-2 is expressed, root hairs are not produced.
3. Analyze the relationship between epidermal cells and cortical cells: In Arabidopsis, root hair formation is influenced by the number of cortical cells an epidermal cell borders. If an epidermal cell borders two cortical cells, GLABRA-2 is not expressed, allowing the formation of a root hair.
4. Evaluate the given statements: The first statement is incorrect because GLABRA-2 expression prevents root hair formation. The second statement is incorrect because GLABRA-2 expression in cells bordering one cortical cell does not lead to root hair formation.
5. Conclude with the correct statement: The correct condition for root hair formation is when an epidermal cell borders two cortical cells, leading to the non-expression of GLABRA-2 and the production of a root hair.