Limits...
FHY1 mediates nuclear import of the light-activated phytochrome A photoreceptor.

Genoud T, Schweizer F, Tscheuschler A, Debrieux D, Casal JJ, Schäfer E, Hiltbrunner A, Fankhauser C - PLoS Genet. (2008)

Bottom Line: In accordance with this idea, FHY1 and FHY3 become functionally dispensable in seedlings expressing a constitutively nuclear version of phyA.Our data suggest that the mechanism uncovered in Arabidopsis is conserved in higher plants.Moreover, this mechanism allows us to propose a model explaining why phyA needs a specific nuclear import pathway.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.

ABSTRACT
The phytochrome (phy) family of photoreceptors is of crucial importance throughout the life cycle of higher plants. Light-induced nuclear import is required for most phytochrome responses. Nuclear accumulation of phyA is dependent on two related proteins called FHY1 (Far-red elongated HYpocotyl 1) and FHL (FHY1 Like), with FHY1 playing the predominant function. The transcription of FHY1 and FHL are controlled by FHY3 (Far-red elongated HYpocotyl 3) and FAR1 (FAr-red impaired Response 1), a related pair of transcription factors, which thus indirectly control phyA nuclear accumulation. FHY1 and FHL preferentially interact with the light-activated form of phyA, but the mechanism by which they enable photoreceptor accumulation in the nucleus remains unsolved. Sequence comparison of numerous FHY1-related proteins indicates that only the NLS located at the N-terminus and the phyA-interaction domain located at the C-terminus are conserved. We demonstrate that these two parts of FHY1 are sufficient for FHY1 function. phyA nuclear accumulation is inhibited in the presence of high levels of FHY1 variants unable to enter the nucleus. Furthermore, nuclear accumulation of phyA becomes light- and FHY1-independent when an NLS sequence is fused to phyA, strongly suggesting that FHY1 mediates nuclear import of light-activated phyA. In accordance with this idea, FHY1 and FHY3 become functionally dispensable in seedlings expressing a constitutively nuclear version of phyA. Our data suggest that the mechanism uncovered in Arabidopsis is conserved in higher plants. Moreover, this mechanism allows us to propose a model explaining why phyA needs a specific nuclear import pathway.

Show MeSH

Related in: MedlinePlus

A constitutively nuclear localized phyA can compensate for the absence of FHY3.(A) Morphology of seedlings grown for 5 days in continuous FR (15 µmol m−2 s−1) light. (B) FR-HIR for inhibition of hypocotyl elongation. Col, phyA-211 and fhy3-1 seedlings as well as phyA-211 seedlings expressing phyA-NLS-GFP or phyA-GFP in FHY3 and fhy3-1 background were grown as in (A). The mean value and the SD are indicated with n>15.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2483295&req=5

pgen-1000143-g006: A constitutively nuclear localized phyA can compensate for the absence of FHY3.(A) Morphology of seedlings grown for 5 days in continuous FR (15 µmol m−2 s−1) light. (B) FR-HIR for inhibition of hypocotyl elongation. Col, phyA-211 and fhy3-1 seedlings as well as phyA-211 seedlings expressing phyA-NLS-GFP or phyA-GFP in FHY3 and fhy3-1 background were grown as in (A). The mean value and the SD are indicated with n>15.

Mentions: It was recently shown that FHY3 and FAR1, two closely related transcription factors, directly regulate the expression of FHY1 and FHL[31]. Given that phyA-NLS-GFP could rescue the fhy1 phenotype, we hypothesized that this construct may also be capable of rescuing fhy3 mutants, in which the major defect appears to be reduced FHY1 and FHL levels. We restricted our analysis to fhy3 mutants because FHY3 plays a significantly more important role for this response than FAR1 [31],[34]. We thus crossed fhy3 with phyA-NLS-GFP plants and analyzed homozygous wild type and mutant fhy3 siblings. Our phenotypic characterization of the response to far-red light showed that while phyA-NLS-GFP rescued the fhy3 mutant phenotype phyA-GFP could not (Figure 6). Our results are thus consistent with the notion that the major function of FHY1 and FHY3 is to respectively operate a directly and indirectly control of phyA nuclear accumulation.


FHY1 mediates nuclear import of the light-activated phytochrome A photoreceptor.

Genoud T, Schweizer F, Tscheuschler A, Debrieux D, Casal JJ, Schäfer E, Hiltbrunner A, Fankhauser C - PLoS Genet. (2008)

A constitutively nuclear localized phyA can compensate for the absence of FHY3.(A) Morphology of seedlings grown for 5 days in continuous FR (15 µmol m−2 s−1) light. (B) FR-HIR for inhibition of hypocotyl elongation. Col, phyA-211 and fhy3-1 seedlings as well as phyA-211 seedlings expressing phyA-NLS-GFP or phyA-GFP in FHY3 and fhy3-1 background were grown as in (A). The mean value and the SD are indicated with n>15.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2483295&req=5

pgen-1000143-g006: A constitutively nuclear localized phyA can compensate for the absence of FHY3.(A) Morphology of seedlings grown for 5 days in continuous FR (15 µmol m−2 s−1) light. (B) FR-HIR for inhibition of hypocotyl elongation. Col, phyA-211 and fhy3-1 seedlings as well as phyA-211 seedlings expressing phyA-NLS-GFP or phyA-GFP in FHY3 and fhy3-1 background were grown as in (A). The mean value and the SD are indicated with n>15.
Mentions: It was recently shown that FHY3 and FAR1, two closely related transcription factors, directly regulate the expression of FHY1 and FHL[31]. Given that phyA-NLS-GFP could rescue the fhy1 phenotype, we hypothesized that this construct may also be capable of rescuing fhy3 mutants, in which the major defect appears to be reduced FHY1 and FHL levels. We restricted our analysis to fhy3 mutants because FHY3 plays a significantly more important role for this response than FAR1 [31],[34]. We thus crossed fhy3 with phyA-NLS-GFP plants and analyzed homozygous wild type and mutant fhy3 siblings. Our phenotypic characterization of the response to far-red light showed that while phyA-NLS-GFP rescued the fhy3 mutant phenotype phyA-GFP could not (Figure 6). Our results are thus consistent with the notion that the major function of FHY1 and FHY3 is to respectively operate a directly and indirectly control of phyA nuclear accumulation.

Bottom Line: In accordance with this idea, FHY1 and FHY3 become functionally dispensable in seedlings expressing a constitutively nuclear version of phyA.Our data suggest that the mechanism uncovered in Arabidopsis is conserved in higher plants.Moreover, this mechanism allows us to propose a model explaining why phyA needs a specific nuclear import pathway.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.

ABSTRACT
The phytochrome (phy) family of photoreceptors is of crucial importance throughout the life cycle of higher plants. Light-induced nuclear import is required for most phytochrome responses. Nuclear accumulation of phyA is dependent on two related proteins called FHY1 (Far-red elongated HYpocotyl 1) and FHL (FHY1 Like), with FHY1 playing the predominant function. The transcription of FHY1 and FHL are controlled by FHY3 (Far-red elongated HYpocotyl 3) and FAR1 (FAr-red impaired Response 1), a related pair of transcription factors, which thus indirectly control phyA nuclear accumulation. FHY1 and FHL preferentially interact with the light-activated form of phyA, but the mechanism by which they enable photoreceptor accumulation in the nucleus remains unsolved. Sequence comparison of numerous FHY1-related proteins indicates that only the NLS located at the N-terminus and the phyA-interaction domain located at the C-terminus are conserved. We demonstrate that these two parts of FHY1 are sufficient for FHY1 function. phyA nuclear accumulation is inhibited in the presence of high levels of FHY1 variants unable to enter the nucleus. Furthermore, nuclear accumulation of phyA becomes light- and FHY1-independent when an NLS sequence is fused to phyA, strongly suggesting that FHY1 mediates nuclear import of light-activated phyA. In accordance with this idea, FHY1 and FHY3 become functionally dispensable in seedlings expressing a constitutively nuclear version of phyA. Our data suggest that the mechanism uncovered in Arabidopsis is conserved in higher plants. Moreover, this mechanism allows us to propose a model explaining why phyA needs a specific nuclear import pathway.

Show MeSH
Related in: MedlinePlus