Question

Predict whether the following plant will undergo photomorphogenesis or skotomophogenesis when grown in the light or in the dark. Briefly justify your answer. Example: A plant with a loss-of-function mutation in the HY5 gene. Example Answer: In the light: Skotomophogenesis, In the dark: Skotomophogenesis HY5 is a transcription factor that directly controls the expression of genes involved with the photomorphogenic response. HY5 is a positive regulator of photomorphogenesis. Recessive mutations in HY5 will result in plants that are unable to undergo photomorphogenesis. (i) A plant over expressing the HYP5 gene. (ii) A plant with a loss-of-function mutation in the COP1 gene. (iii) A phycop1 double mutant plant (both recessive mutations).

Answer 1

Given cases respctively are:

(i) A plant over expressing the HYP5 gene.

Answer: In Light- Photomorphogenesis ; In Dark- Skotomorphogenesis

HYP5 gene is responsible for photomorphogenesis and during the day light the other regulatory gene i.e. COP1 remains inactive (an inhibitor of HY5), overexpression of HY5 will result in Photomorphogenesis. While in dark although it is overexpressing but at the same time overruled by the effect of other inhibitory/regulatory genes like COP1 (as they are in their normal form), thus results Skotomorphogenesis.     

(ii) A plant with a loss-of-function mutation in the COP1 gene.

Answer: In Light- Photomorphogenesis ; In Dark- Photomorphogenesis

As discussed in previously mentioned answer, COP1 results Skotomorphogenesis by inhibiting HY5 in dark. Due to loss-of-function mutation in the COP1 gene it is unable to inhibit HY5 and thus results Photomorphogenesis.

(iii) A phycop1 double mutant plant (both recessive mutations).

Answer: In Light- Photomorphogenesis ; In Dark- Skotomorphogenesis

As the mutations in the plant are recessive mutations, it will not affect the normal funtioning of the plant. For more clarification phy-cop1 genes are directly/indirectly are stabilizers of bZIP transcription factors i.e. HY5. And as discussed earlier HY5 normally function in photomorphogenesis in day time.

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