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Ubiquitin ligase switch in plant photomorphogenesis: A hypothesis.

Pokhilko A, Ramos JA, Holtan H, Maszle DR, Khanna R, Millar AJ - J. Theor. Biol. (2010)

Bottom Line: This leads to accumulation of COP1's target transcription factors, which initiates photomorphogenesis, resulting in dramatic changes of the seedling's physiology.CUL4 activity is predicted to increase in the presence of light.We propose that the ubiquitin ligase switch is important for the complex regulation of multiple transcription factors during plants development.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JH, United Kingdom. apokhilk@staffmail.ed.ac.uk

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Simulated kinetics of the model components under various photoperiods. The simulations were initially run for 4 days under each photoperiod to entrain the system, so that only 5th and 6th days are shown. A, B: Solid, dashed and dashed-dotted lines correspond to 6 L:18 D, 12 L:12 D and 18 L:6 D light–dark cycles, respectively. Blue, black, green and magenta colors show the kinetics of HFR1, HY5 proteins and the activity of COP1 and CUL4 respectively. C: Simulated kinetics of the hypothetical COP1 (blue) and CUL4 (red) substrates under 12L:12D. HFR1 equation was used for COP1 substrate with the following parameter values: p5=0.28 h−1; h7=2 h−1. HY5 protein equation was used for CUL4 substrate with constant expression level p4 and the following parameter values: p4=0.22 h−1; h4=1 h−1; h5=0. The rest of the parameters are shown in Table 2 of the Appendix.
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f0030: Simulated kinetics of the model components under various photoperiods. The simulations were initially run for 4 days under each photoperiod to entrain the system, so that only 5th and 6th days are shown. A, B: Solid, dashed and dashed-dotted lines correspond to 6 L:18 D, 12 L:12 D and 18 L:6 D light–dark cycles, respectively. Blue, black, green and magenta colors show the kinetics of HFR1, HY5 proteins and the activity of COP1 and CUL4 respectively. C: Simulated kinetics of the hypothetical COP1 (blue) and CUL4 (red) substrates under 12L:12D. HFR1 equation was used for COP1 substrate with the following parameter values: p5=0.28 h−1; h7=2 h−1. HY5 protein equation was used for CUL4 substrate with constant expression level p4 and the following parameter values: p4=0.22 h−1; h4=1 h−1; h5=0. The rest of the parameters are shown in Table 2 of the Appendix.

Mentions: HFR1 and HY5 proteins represented two classes of COP1 targets with fast and slow kinetics, respectively. The observed accumulation of HY5 after transition of plants to light and its depletion in darkness was much slower than for HFR1 (Figs. 4 and 5). The model explained these experimental observations by the higher efficiency of COP1-mediated degradation of the “fast” substrates, such as HFR1. The differences in the kinetics of the fast and slow COP1 targets were further demonstrated by simulations of diurnal conditions with various photoperiods. Fig. 6A shows the fast transient accumulation of HFR1 protein in the morning under all photoperiods, which resulted from the transient fall and then restoration of COP1 activity (Fig. 6B). HY5 protein had slower kinetics and stayed at high level during the whole light period (Fig. 6A), when HY5 expression is high. Thus the model predicted a higher level of HY5 protein under long summer days (18 h of light) compared to the short winter days (6 h of light) (Fig. 6A), which would result in the prolonged stimulation of downstream processes, such as anthocyanin biosynthesis (Ang et al., 1998). We also demonstrated the opposite regulation of COP1 and CUL4 activities by light, which resulted in decrease of COP1 activity and increase of CUL4 activity in light and the opposite trends in darkness (Fig. 6B). The model predicted an increase of the maximal level of COP1 activity in short days compared to long days (Fig. 6B).


Ubiquitin ligase switch in plant photomorphogenesis: A hypothesis.

Pokhilko A, Ramos JA, Holtan H, Maszle DR, Khanna R, Millar AJ - J. Theor. Biol. (2010)

Simulated kinetics of the model components under various photoperiods. The simulations were initially run for 4 days under each photoperiod to entrain the system, so that only 5th and 6th days are shown. A, B: Solid, dashed and dashed-dotted lines correspond to 6 L:18 D, 12 L:12 D and 18 L:6 D light–dark cycles, respectively. Blue, black, green and magenta colors show the kinetics of HFR1, HY5 proteins and the activity of COP1 and CUL4 respectively. C: Simulated kinetics of the hypothetical COP1 (blue) and CUL4 (red) substrates under 12L:12D. HFR1 equation was used for COP1 substrate with the following parameter values: p5=0.28 h−1; h7=2 h−1. HY5 protein equation was used for CUL4 substrate with constant expression level p4 and the following parameter values: p4=0.22 h−1; h4=1 h−1; h5=0. The rest of the parameters are shown in Table 2 of the Appendix.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3021735&req=5

f0030: Simulated kinetics of the model components under various photoperiods. The simulations were initially run for 4 days under each photoperiod to entrain the system, so that only 5th and 6th days are shown. A, B: Solid, dashed and dashed-dotted lines correspond to 6 L:18 D, 12 L:12 D and 18 L:6 D light–dark cycles, respectively. Blue, black, green and magenta colors show the kinetics of HFR1, HY5 proteins and the activity of COP1 and CUL4 respectively. C: Simulated kinetics of the hypothetical COP1 (blue) and CUL4 (red) substrates under 12L:12D. HFR1 equation was used for COP1 substrate with the following parameter values: p5=0.28 h−1; h7=2 h−1. HY5 protein equation was used for CUL4 substrate with constant expression level p4 and the following parameter values: p4=0.22 h−1; h4=1 h−1; h5=0. The rest of the parameters are shown in Table 2 of the Appendix.
Mentions: HFR1 and HY5 proteins represented two classes of COP1 targets with fast and slow kinetics, respectively. The observed accumulation of HY5 after transition of plants to light and its depletion in darkness was much slower than for HFR1 (Figs. 4 and 5). The model explained these experimental observations by the higher efficiency of COP1-mediated degradation of the “fast” substrates, such as HFR1. The differences in the kinetics of the fast and slow COP1 targets were further demonstrated by simulations of diurnal conditions with various photoperiods. Fig. 6A shows the fast transient accumulation of HFR1 protein in the morning under all photoperiods, which resulted from the transient fall and then restoration of COP1 activity (Fig. 6B). HY5 protein had slower kinetics and stayed at high level during the whole light period (Fig. 6A), when HY5 expression is high. Thus the model predicted a higher level of HY5 protein under long summer days (18 h of light) compared to the short winter days (6 h of light) (Fig. 6A), which would result in the prolonged stimulation of downstream processes, such as anthocyanin biosynthesis (Ang et al., 1998). We also demonstrated the opposite regulation of COP1 and CUL4 activities by light, which resulted in decrease of COP1 activity and increase of CUL4 activity in light and the opposite trends in darkness (Fig. 6B). The model predicted an increase of the maximal level of COP1 activity in short days compared to long days (Fig. 6B).

Bottom Line: This leads to accumulation of COP1's target transcription factors, which initiates photomorphogenesis, resulting in dramatic changes of the seedling's physiology.CUL4 activity is predicted to increase in the presence of light.We propose that the ubiquitin ligase switch is important for the complex regulation of multiple transcription factors during plants development.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JH, United Kingdom. apokhilk@staffmail.ed.ac.uk

Show MeSH
Related in: MedlinePlus