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Investigations on the photoregulation of chloroplast movement and leaf positioning in Arabidopsis.

Han IS, Cho HY, Moni A, Lee AY, Briggs WR - Plant Cell Physiol. (2012)

Bottom Line: The effect is far-red reversible.This photoreversible response is normal in a phyB mutant but does not appear in a phyA mutant.These results suggest that phyA mediates the enhancement, induced by a red light pulse, of blue light-induced chloroplast movements.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Ulsan, Ulsan 680-749, Korea. hanis@ulsan.ac.kr

ABSTRACT
We recently investigated the roles of the phototropin 1 (PHOT1) LOV (light, oxygen or voltage) domains in mediating phototropic curvature in transgenic Arabidopsis seedlings expressing either wild-type PHOT1 or PHOT1 with one or both LOV domains inactivated by a single amino acid replacement. We have now investigated the role of the PHOT1 LOV domains in chloroplast movement and in leaf positioning in response to blue light. Low fluence rate blue light is known to mediate a chloroplast accumulation response and high fluence rate blue light an avoidance response in Arabidopsis leaves. As was the case for phototropism, LOV2 of PHOT1 is essential for chloroplast accumulation and LOV1 is dispensable. PHOT1 LOV2 is also essential to maintain developing primary leaves in a horizontal position under white light from above and LOV1 is again dispensable. A red light pulse given to dark-adapted light-grown plants followed by 2 h of darkness enhances both the chloroplast accumulation response under dim blue light and the chloroplast avoidance response under strong blue light. The effect is far-red reversible. This photoreversible response is normal in a phyB mutant but does not appear in a phyA mutant. These results suggest that phyA mediates the enhancement, induced by a red light pulse, of blue light-induced chloroplast movements.

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Western blots of membrane fractions prepared from seven different Arabidopsis lines and probed with anti-PHOT2 antibody. Note that the transformant lines 5-a, 5-c and 5-d express levels of PHOT2 far below those of the wild type (gl1) or phot1-5. Lines 5-a and 5-d do not appear to express more protein than the phot1 phot2 double mutant although line 5-d does show some limited complementation (see text).
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pcs098-F2: Western blots of membrane fractions prepared from seven different Arabidopsis lines and probed with anti-PHOT2 antibody. Note that the transformant lines 5-a, 5-c and 5-d express levels of PHOT2 far below those of the wild type (gl1) or phot1-5. Lines 5-a and 5-d do not appear to express more protein than the phot1 phot2 double mutant although line 5-d does show some limited complementation (see text).

Mentions: To test this hypothesis, we carried out Western blot analysis and chloroplast movement experiments for lines 5-a, 5-c and 5-d from Cho et al. (2007) that had all been transformed with the fully functional PHOT2 gene. These lines all showed mRNA levels above those for wild-type PHOT2 plants (Cho et al. 2007). Line 5-c showed the highest expression both of the phot2 transgene (fig. 1C in Cho et al. 2007) and of the PHOT2 protein (Fig. 2). Not surprisingly, line 5-a was no different from the phot1 phot2 double mutant and failed to show any chloroplast response (Fig. 3). Line 5-d showed slight accumulation at both light intensities, somewhat above that shown by the double mutant. However, line 5-c, with its higher expression level (Fig. 2), actually showed a significant avoidance response at the higher fluence rate (Fig. 3). Evidently the levels of PHOT2 protein present were sufficient for an avoidance response in this case. Note that line 5-c (Fig. 2) shows two bands. This is also the case for lines 7-a, 8-a-2 and 8-c-2 (Supplementary Fig. S1). All of these lines show expression of mRNA well above the basal level seen in the phot1 phot2 double mutant. We attribute the lower band to leaky expression of the wild-type gene. We suggest that the protein from the transgene is fully phosphorylated whereas the leaked protein from the mutant gene is not. The separation is what we would expect if the difference is the consequence of differential phosphorylation (see Cho et al. 2007, fig. 7, lanes 2 and 4 to compare unphosphorylated and phosphorylated phot2.Fig. 2


Investigations on the photoregulation of chloroplast movement and leaf positioning in Arabidopsis.

Han IS, Cho HY, Moni A, Lee AY, Briggs WR - Plant Cell Physiol. (2012)

Western blots of membrane fractions prepared from seven different Arabidopsis lines and probed with anti-PHOT2 antibody. Note that the transformant lines 5-a, 5-c and 5-d express levels of PHOT2 far below those of the wild type (gl1) or phot1-5. Lines 5-a and 5-d do not appear to express more protein than the phot1 phot2 double mutant although line 5-d does show some limited complementation (see text).
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3539441&req=5

pcs098-F2: Western blots of membrane fractions prepared from seven different Arabidopsis lines and probed with anti-PHOT2 antibody. Note that the transformant lines 5-a, 5-c and 5-d express levels of PHOT2 far below those of the wild type (gl1) or phot1-5. Lines 5-a and 5-d do not appear to express more protein than the phot1 phot2 double mutant although line 5-d does show some limited complementation (see text).
Mentions: To test this hypothesis, we carried out Western blot analysis and chloroplast movement experiments for lines 5-a, 5-c and 5-d from Cho et al. (2007) that had all been transformed with the fully functional PHOT2 gene. These lines all showed mRNA levels above those for wild-type PHOT2 plants (Cho et al. 2007). Line 5-c showed the highest expression both of the phot2 transgene (fig. 1C in Cho et al. 2007) and of the PHOT2 protein (Fig. 2). Not surprisingly, line 5-a was no different from the phot1 phot2 double mutant and failed to show any chloroplast response (Fig. 3). Line 5-d showed slight accumulation at both light intensities, somewhat above that shown by the double mutant. However, line 5-c, with its higher expression level (Fig. 2), actually showed a significant avoidance response at the higher fluence rate (Fig. 3). Evidently the levels of PHOT2 protein present were sufficient for an avoidance response in this case. Note that line 5-c (Fig. 2) shows two bands. This is also the case for lines 7-a, 8-a-2 and 8-c-2 (Supplementary Fig. S1). All of these lines show expression of mRNA well above the basal level seen in the phot1 phot2 double mutant. We attribute the lower band to leaky expression of the wild-type gene. We suggest that the protein from the transgene is fully phosphorylated whereas the leaked protein from the mutant gene is not. The separation is what we would expect if the difference is the consequence of differential phosphorylation (see Cho et al. 2007, fig. 7, lanes 2 and 4 to compare unphosphorylated and phosphorylated phot2.Fig. 2

Bottom Line: The effect is far-red reversible.This photoreversible response is normal in a phyB mutant but does not appear in a phyA mutant.These results suggest that phyA mediates the enhancement, induced by a red light pulse, of blue light-induced chloroplast movements.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Ulsan, Ulsan 680-749, Korea. hanis@ulsan.ac.kr

ABSTRACT
We recently investigated the roles of the phototropin 1 (PHOT1) LOV (light, oxygen or voltage) domains in mediating phototropic curvature in transgenic Arabidopsis seedlings expressing either wild-type PHOT1 or PHOT1 with one or both LOV domains inactivated by a single amino acid replacement. We have now investigated the role of the PHOT1 LOV domains in chloroplast movement and in leaf positioning in response to blue light. Low fluence rate blue light is known to mediate a chloroplast accumulation response and high fluence rate blue light an avoidance response in Arabidopsis leaves. As was the case for phototropism, LOV2 of PHOT1 is essential for chloroplast accumulation and LOV1 is dispensable. PHOT1 LOV2 is also essential to maintain developing primary leaves in a horizontal position under white light from above and LOV1 is again dispensable. A red light pulse given to dark-adapted light-grown plants followed by 2 h of darkness enhances both the chloroplast accumulation response under dim blue light and the chloroplast avoidance response under strong blue light. The effect is far-red reversible. This photoreversible response is normal in a phyB mutant but does not appear in a phyA mutant. These results suggest that phyA mediates the enhancement, induced by a red light pulse, of blue light-induced chloroplast movements.

Show MeSH