- Some of the following transgenic approaches could be used for functional characterization of endogenous genes in plants:
(A) Transformation using a binary vector containing a strong enhancer element and lacking the right border of T-DNA
(B) Transformation using a binary vector containing a promoter-less reporter gene sequence and a selection maker gene cassette within the T-DNA.
(C) Transformation using a binary vector containing only a strong enhancer element and a selection marker gene cassette within the T-DNA.
(D) Transformation using a binary vector lacking a reporter gene as well as both the left and right borders of T-DNA.
Which one of the following combinations can be used?
(1) A and B only (2) B and C only
(3) C and D only (4) A and D onlyThe suitable approaches are (2) B and C only.
Understanding the strategies
Functional genomics in plants often relies on:
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Gene traps / promoterless reporter constructs – identify endogenous promoters when T-DNA inserts into or near genes.
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Enhancer traps – place a minimal or heterologous promoter plus enhancer element to respond to nearby enhancers and report tissue‑specific activity.
T‑DNA must have both left and right borders for efficient transfer and integration.
Option-by-option analysis
(A) Strong enhancer element but lacking the right border – Not usable
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Without the right border (RB), the T‑DNA region is not correctly delimited; Agrobacterium’s transfer machinery uses both LB and RB to excise and transfer the T‑strand.
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A construct missing RB will not reliably integrate as intended, so it is not a valid functional-genomics tool.
(B) Promoter‑less reporter gene + selection marker within T‑DNA – Usable
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This is a classic gene trap design:
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The reporter gene (e.g., GUS, GFP) has no promoter.
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When T‑DNA inserts into an expressed gene or downstream of its promoter, endogenous transcription drives the reporter.
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Insertion pattern and reporter expression reveal where and when the trapped gene is active, allowing functional characterization.
(C) Strong enhancer element + selection marker within T‑DNA – Usable
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This corresponds to an enhancer trap:
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A strong enhancer (often combined with a minimal or heterologous promoter in practice) is responsive to nearby genomic regulatory elements.
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When the T‑DNA lands near an endogenous gene, the enhancer can up‑ or mis‑express that gene, producing gain‑of‑function phenotypes or reporter patterns that help deduce gene function.
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Thus C is an appropriate functional-genomics strategy.
(D) Lacking reporter gene and both T‑DNA borders – Not usable
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Without both LB and RB, there is no defined T‑DNA to transfer; Agrobacterium cannot deliver the cassette efficiently.
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With no reporter gene either, even rare random integrations cannot be easily detected or interpreted.
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This construct cannot serve as a practical tool for gene function analysis.
Why option (2) is correct
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B and C describe standard gene trap and enhancer trap-type constructs that are widely used to functionally characterize endogenous genes.
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Constructs A and D lack essential T‑DNA borders or functional reporters and therefore are not suitable.
So the correct combination is (2) B and C only.
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