Intercellular Communication

Question 1

Photoperiodism: In the morning…?

Answer 1

CCA1 is active, represses FKF1 expression

CDF1 represses CO expression

Question 2

Photoperiodism: In the afternoon…?

Answer 2

CCA1 i degraded by SCF E3 Ub ligase

FKF1 is expressed, forms F-box protein of SCF E3 Ub Ligase, which DEGRADES CDF1

CO can be expressed

Question 3

Light-mediated oscillator:

In the dark…?
In the light….?

Answer 3

In the dark:

COP1 E3 Ub Ligase degrades CO

In the light:
Pfr is active, translocates to nucleus, inhibits COP1.
Cryptochromes bind and sequester COP1 in the cytosol

Question 4

Repression of competency during juvenile phase

Answer 4

miR156, targets certain mRNA for degradation

miR156 levels increases with sugar levels - so mature plant gains competency

Question 5

Long-distance signal

Answer 5

Florigen (FT locus)

Shown by grafting leaves from inductive photoperiods to non-inductive photoperiods

CO expression in leaves induces FT expression in leaves and phloem, and apical meristem

Expression of CO in apical meristem results in flowering

Question 6

Repression of competency by FLC

Answer 6

FLC is a MADS box TF, negatively regulates competence by repressing FT expression

Vernalisation and autonomous pathway

Question 7

Vernalisation

Answer 7

VIN3 - deacetylates and methylates H3K27

VRN2 - maintains H3K27me3 (homologous to Polycomb)

COLDAIR - first intron of FLC
Sense transcripts help recruit polycomb proteins

Antisense transcripts mediate RNAi

Question 8

Autonomous Pathway

Answer 8

Epigenetic modifications + RNAi silences FLC
Decrease in miR156

Results in increase in competence