Submitted by: Submitted by lindayin08
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Category: Science and Technology
Date Submitted: 04/08/2011 11:20 PM
Arabidopsis — A Model System for Plant Molecular Genetic Studies
Light Affects Seedling Development
These affects of light are mediated by two classes of photoreceptors: the Phytochromes (respond to red/far-red light) and the Cryptochromes (respond to blue light).
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A Mutant Arabidopsis Seedling Grows in the Light as if it were Growing in the Dark
Mode of action of photolyases
The mutant was selectively insensitive to blue light — it grew like wild-type under red light.
The mutant Arabidopsis gene encoded a protein similar in sequence to that of photolyase proteins. Photolyases mediate DNA repair in response to blue light.
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CRY1 is a flavoprotein
Like photolyases, cryptochromes are flavoproteins — however, they lack photolyase activity
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Arabidopsis CRY1 and CRY2 contain a photolyase-like N-terminal domain (CNT) and a distinguishing C-terminal domain (CCT)
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Arabidopsis Plants were Engineered to Express a Gene Containing the C-terminal Domain of CRY1
Plants Expressing the CRY1 C-terminal Domain Exhibit a Constitutive Light Response
The Transgenic Seedling (on the right) grows in the Dark as if it were Growing in the Light.
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Transgenic Plants Expressing Mutant C-terminii do not Exhibit a Constitutive Light Response
Multiple cry1 alleles
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A simple model of cryptochrome activity, based on the mode of action of photolyase
The isolated “active” form of CCT mediates a constitutive light response
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In this model, CCT undergoes no change in response to light
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The CCT domain of CRY is inactive in the dark as a result of negative regulation by CNT
The negative regulation of CCT by CNT is alleviated through the action of light
Isolated CCT exists in a similarly active form
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COP1: an E3 Ubiquitin Ligase
The “Looping DNA” Model Explains the Activity of Enhancer Sequences
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Osterlund et al., 2000
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The Yeast 2-Hybrid...