1. Cryptochrome is a major blue light photoreceptor in plants that regulates processes like photomorphogenesis, circadian rhythms, and flowering. 2. There are three types of cryptochrome found in Arabidopsis - CRY1, CRY2, and CRY3. CRY1 and CRY2 are involved in photomorphogenesis while CRY3 functions in DNA repair in mitochondria and chloroplasts. 3. Cryptochrome has two domains - an amino-terminal photolyase homology region that binds chromophores like FAD and perceives blue light, and a carboxy-terminal output domain that transduces the light signal.

1. CRYPTOCHROME

2. 2
TYPES OF PHOTORECEPTORS
1. Phytochrome (Red Light Photoreceptor) Plays a role in seed
germination, flowering and stem elongation etc.
2. Cryptochrome (Blue Light Photoreceptor) Plays a role in flowering,
circadian rhythms and inhibition of stem elongation etc.
3. Phototropin (Blue Light Photoreceptor) Plays a role in chloroplast
movement and phototropism etc
4. Zeitlupe family (Blue Light Photoreceptor) plays a role in circadian
rhythms and control of flowering.
There are 4 major types of photoreceptors involved in photomorphogenesis:

3. Photoreceptor
Associated With
Blue Light
Response.

4. CRY1
It is located equally in both
nucleus and cytoplasm. It is blue
light photoreceptor of plant and
promotes photomorphogenesis.
CRY 2
CRY 2-It is exclusively localized in
nucleus. It is blue light
photoreceptor of plant and
promotes photomorphogenesis.
CRY 3
CRY 3-It is CRY-DASH type of CRY
present in Mitochondria and chloroplast
and functions to repair UV induced
damage on ssDNA. It is not a blue light
photoreceptor that promotes
photomorphogenesis
CRYPTOCHROME UNIQUE PROPERTIES
 Cryptochrome is structurally similar to photolyase a blue light activated Enzyme
that repairs pyrimidine dimers in DNA. But cryptochrome do not have any role in
DNA repairs, but they are thought to have evolved from photolyase enzyme
➤ In Arabidopsis, 3 cryptochrome genes are reported
• The major difference between CRY1 & CRY2 is that Cry1 is stable in the presence of blue light
while CRY 2 undergoes degradation under blue light.

5.  Cryptochrome is a dimeric flavoprotein dimerization is essential for their activity
and it is mediated by the blue light sensory PHR domain.
 Cryptochrome undergoes blue light dependent homodimerization and
photoactivation.
 In CRY blue light is absorbed by Pterin (MTHF) and is
transferred to FAD. FAD is the primary chromophore
regulating cryptochrome activity.
 Blue light is perceived by PHR domain & is
transferred to CCT domain to start the signaling
pathway.

6. CRYPTOCHROME SPECIAL PROPERTY
 Cryptochrome are structurally related to photolyase. Photolyase is
a blue light activated enzyme that repairs pyrimidine dimer in DNA.
 The Cryptochrome do not have a DNA repair activity, but they are
thought to have evolved from the photolyase.
 Cryptochrome play a very important role in the generation and
maintenance of circadian rhythm(biological clock)

7. Photolyase homology region CCT DAS
FAD
MTHF
N C
Domain Structure Of Plant Cytochrome
Cryptochrome consists of 2 domains:
1. Amino Terminal Photolyase Homology region (PHR) which binds
2. Chromophores
non-covalently. It is sensor domain.
A. Flavin which is FAD
B. Pterin which is MTHF
Cryptochrome Carboxyl Terminal (CCT) Domain - within the CCT there is a sub domain known as
DAS at carboxyl terminal. It is the output domain.

8. 1.Dimerization is essential for biological activity and is
mediated by N-terminal domain.
2.The C-terminal domain transduce the light signal by
interacting with the E3 ubiquitin ligase, COP1 (CONSTITUTIVE
PHOTOMORPHOGENIC 1)
STRUCTURAL DOMAIN

9. MODELS OF CRYPTOCHROME
There are two models of cryptochrome
1. Closed Model:
Under dark conditions PHR domain binds CCT domain tightly repressing CCT domain activity in
the absence of light
2. Open Model:
• Upon the absorption of blue light by PHR domain there is slight conformational change which
results in homodimerization & autophosphorylation of CCT domain on multiple serine
residues which causes electrostatic repulsion of CCT domain from PHR domain.
• That results in deattachment of CCT domain from PHR domain there by making multiple sites
accessible for phosphorylation by unidentified kinase "Y".
• So phosphorylation plays important role in derepression of CCT domain from PHR domain
which results in its photoactivation of cryptochrome.

10. MUTATION CASES OF CRY1, CRY2 & COP1
CRY1 plays a primary role
in de-etiolation of plants
and CRY2 plays a primary
role in photoperiodic
flowering.
Mutation of CRY1, CRY2 &
COP11.
Mutation in CRY2 led to delayed
flowering under blue light.
Overexpression of CRY2 leads to early
flowering
Mutation in CRY1 results in elongated
hypocotyl and etiolated growth in blue light.
Overexpression of CRY1 results in strong inhibition
of hypocotyl and overproduction of anthocyanin.
COP1 mutant displace constitutive photo
morphogeneic phenotype in which dark grown
seedlings mimic light grown seedlings.

11. 1. CRY1 plays a primary role in inhibition of stem elongation.
2. CRY1 plays a primary role in leaf expansion.
3. CRY2 plays a primary role in promotion of photoperiodic flowering.
4. CRY2 promotes photoperiodic flowering in Arabidopsis.
5. CRY1 plays major role & to some extent CRY2 plays a
role in setting circadian rhythm in plants and animals.
6. CRY1 promotes cotyledons expansion.
7. CRY1 promotes anthocyanin production.
8. CRY1 inhibits petiole elongation.
9. CRY1 also serve as magnetoreceptors in Animals.

12. 1. Help in Anthocyanin production.
2. Stomatal opening.
3. Circadian clock.
4. Cryptochrome are evolutionarily old and highly conserved proteins.
5. Phototropism
6. Photomorphogenesis
7. Light capture
8. Inhibition of stem elongation.
9. Circadian rhythm
10. Magnetoreception-sensing of magnetic fields in a number of special

13. CCT SPA1
COP1
LAF1
HY5
HFR1
Photomorphogenesis
Kinase Y
P
Light
Responsive
gene
+
+
Active
Inactive
CRY1
Active
 In mutant CRY1, N-terminal PHR domain
is non-functional and CCT conformation
even in the absence of light due to
constitutive domain can form active
phosphorylation.
 Active CCT domain inhibits COP1 SPA1
activity even in darkness there by
preventing degradation of
photomorphogenesis promoting
transcription factors like HFR1, HYS, LAF1.
 So accumulation of HY5, HFR1 & LAF1
proteins in the nucleus promotes
photomorphogenesis even in darkness.
CCT overexpression mutant; Dark
& Light
Nucleus

14. LAF1
HY5
HFR1
Photomorphogenesis
Kinase Y
Light
Responsive
gene
+
+
Active
Nucleus
PHR
PHR
Inactive
Inactive
Active CRY 1
Dimer
 Photoactivated CRY1 binds to SPA1 in COP1
SPA1 complex via CCT domain resulting in
dissociation of COP1-SPA1 complex which
inhibits COP1 activity.
 This prevents the degradation of
photomorphogenesis promoting transcription
factors like HY5, HFR1 & LAF1.
 In Blue light CRY1 undergoes homo dimerization
via PHR domain which partially activates CRY1 &
promotes blue light dependent Autophosporylation
of CCT domain & phosphorylation by unknown
 kinase "Y" which fully activates CRY1 in the
nucleus.
 This promotes photomorphogenesis in presence of blue
light.
LIGHT

15. CCT
PHR
Inactive CRY 1 monomer
 In dark, CRY1 remains inactive in the
nucleus in form of monomer.
 In dark, COP1 (E3 ubiquitin ligase) & SPA1
forms complex in the nucleus which
positively regulates COP1 activity.
 COP1-SPA1 complex degrade
photomorphogenesis promoting
transcription factors like HY5,HFR1 & LAF1
via. Ubiquitin mediated 265 proteasome
degradation.
 This inhibits photomorphogenesis and
promotes etiolated growth of plants in
dark.
Nucleus