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Light plays an essential role in intracellular distribution of auxin efflux carrier PIN2 in Arabidopsis thaliana.

Laxmi A, Pan J, Morsy M, Chen R - PLoS ONE (2008)

Bottom Line: Using laser confocal scanning microscopy, and physiological and molecular genetic approaches, here, we show that in dark-grown seedlings, the PM localization of auxin efflux carrier PIN2 was largely reduced, and, in addition, PIN2 signal was detected in vacuolar compartments.In addition, the ubiquitin 26S proteasome is involved in the process, since its inhibition by mutations in COP9 and a proteasome inhibitor MG132 impaired the process.Based on these results, we postulate that light regulation of root development is mediated at least in part by changes in the intracellular distribution of auxin efflux carriers, PIN proteins, in response to the light environment.

View Article: PubMed Central - PubMed

Affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, Oklahoma, USA.

ABSTRACT

Background: Light plays a key role in multiple plant developmental processes. It has been shown that root development is modulated by shoot-localized light signaling and requires shoot-derived transport of the plant hormone, auxin. However, the mechanism by which light regulates root development is not largely understood. In plants, the endogenous auxin, indole-3-acetic acid, is directionally transported by plasma-membrane (PM)-localized auxin influx and efflux carriers in transporting cells. Remarkably, the auxin efflux carrier PIN proteins exhibit asymmetric PM localization, determining the polarity of auxin transport. Similar to PM-resident receptors and transporters in animal and yeast cells, PIN proteins undergo constitutive cycling between the PM and endosomal compartments. Auxin plays multiple roles in PIN protein intracellular trafficking, inhibiting PIN2 endocytosis at some concentrations and promoting PIN2 degradation at others. However, how PIN proteins are turned over in plant cells is yet to be addressed.

Methodology and principle findings: Using laser confocal scanning microscopy, and physiological and molecular genetic approaches, here, we show that in dark-grown seedlings, the PM localization of auxin efflux carrier PIN2 was largely reduced, and, in addition, PIN2 signal was detected in vacuolar compartments. This is in contrast to light-grown seedlings where PIN2 was predominantly PM-localized. In light-grown plants after shift to dark or to continuous red or far-red light, PIN2 also accumulated in vacuolar compartments. We show that PIN2 vacuolar targeting was derived from the PM via endocytic trafficking and inhibited by HY5-dependent light signaling. In addition, the ubiquitin 26S proteasome is involved in the process, since its inhibition by mutations in COP9 and a proteasome inhibitor MG132 impaired the process.

Conclusions and significance: Collectively, our data indicate that light plays an essential role in PIN2 intracellular trafficking, promoting PM-localization in the presence of light and, on the other hand, vacuolar targeting for protein degradation in the absence of light. Based on these results, we postulate that light regulation of root development is mediated at least in part by changes in the intracellular distribution of auxin efflux carriers, PIN proteins, in response to the light environment.

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PIN2-eGFP intracellular distribution in excised roots.Four-day-old light grown PIN2-eGFP seedlings, after removal of cotyledons, were transferred to either light (A) or dark (B) for 10 hrs. PIN2-eGFP was localized to the PM in excised roots incubated in the presence of light (A). By contrast, PIN2-eGFP was accumulated in vacuolar compartments in excised roots incubated in the absence of light (B). Shown in right were close-up images. Scale bars, 50 µm (left); 10 µm (right).
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pone-0001510-g008: PIN2-eGFP intracellular distribution in excised roots.Four-day-old light grown PIN2-eGFP seedlings, after removal of cotyledons, were transferred to either light (A) or dark (B) for 10 hrs. PIN2-eGFP was localized to the PM in excised roots incubated in the presence of light (A). By contrast, PIN2-eGFP was accumulated in vacuolar compartments in excised roots incubated in the absence of light (B). Shown in right were close-up images. Scale bars, 50 µm (left); 10 µm (right).

Mentions: We tested whether similar patterns of PIN2 intracellular distribution occur in excised roots in response to the light environment. For this, we removed cotyledons from 4-day-old light-grown seedlings and transferred the excised roots to either continuous light or dark for 10 hrs, and examined the PIN2-eGFP localization. These data indicate that PIN2-eGFP was accumulated in vacuolar compartments of excised roots incubated in absence of light, but not of excised roots incubated in the presence of light (Figs. 8A, B). These data suggest that excised roots similar to intact whole seedlings can sense the light condition in regulating PIN2 protein intracellular localization.


Light plays an essential role in intracellular distribution of auxin efflux carrier PIN2 in Arabidopsis thaliana.

Laxmi A, Pan J, Morsy M, Chen R - PLoS ONE (2008)

PIN2-eGFP intracellular distribution in excised roots.Four-day-old light grown PIN2-eGFP seedlings, after removal of cotyledons, were transferred to either light (A) or dark (B) for 10 hrs. PIN2-eGFP was localized to the PM in excised roots incubated in the presence of light (A). By contrast, PIN2-eGFP was accumulated in vacuolar compartments in excised roots incubated in the absence of light (B). Shown in right were close-up images. Scale bars, 50 µm (left); 10 µm (right).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2200863&req=5

pone-0001510-g008: PIN2-eGFP intracellular distribution in excised roots.Four-day-old light grown PIN2-eGFP seedlings, after removal of cotyledons, were transferred to either light (A) or dark (B) for 10 hrs. PIN2-eGFP was localized to the PM in excised roots incubated in the presence of light (A). By contrast, PIN2-eGFP was accumulated in vacuolar compartments in excised roots incubated in the absence of light (B). Shown in right were close-up images. Scale bars, 50 µm (left); 10 µm (right).
Mentions: We tested whether similar patterns of PIN2 intracellular distribution occur in excised roots in response to the light environment. For this, we removed cotyledons from 4-day-old light-grown seedlings and transferred the excised roots to either continuous light or dark for 10 hrs, and examined the PIN2-eGFP localization. These data indicate that PIN2-eGFP was accumulated in vacuolar compartments of excised roots incubated in absence of light, but not of excised roots incubated in the presence of light (Figs. 8A, B). These data suggest that excised roots similar to intact whole seedlings can sense the light condition in regulating PIN2 protein intracellular localization.

Bottom Line: Using laser confocal scanning microscopy, and physiological and molecular genetic approaches, here, we show that in dark-grown seedlings, the PM localization of auxin efflux carrier PIN2 was largely reduced, and, in addition, PIN2 signal was detected in vacuolar compartments.In addition, the ubiquitin 26S proteasome is involved in the process, since its inhibition by mutations in COP9 and a proteasome inhibitor MG132 impaired the process.Based on these results, we postulate that light regulation of root development is mediated at least in part by changes in the intracellular distribution of auxin efflux carriers, PIN proteins, in response to the light environment.

View Article: PubMed Central - PubMed

Affiliation: Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, Oklahoma, USA.

ABSTRACT

Background: Light plays a key role in multiple plant developmental processes. It has been shown that root development is modulated by shoot-localized light signaling and requires shoot-derived transport of the plant hormone, auxin. However, the mechanism by which light regulates root development is not largely understood. In plants, the endogenous auxin, indole-3-acetic acid, is directionally transported by plasma-membrane (PM)-localized auxin influx and efflux carriers in transporting cells. Remarkably, the auxin efflux carrier PIN proteins exhibit asymmetric PM localization, determining the polarity of auxin transport. Similar to PM-resident receptors and transporters in animal and yeast cells, PIN proteins undergo constitutive cycling between the PM and endosomal compartments. Auxin plays multiple roles in PIN protein intracellular trafficking, inhibiting PIN2 endocytosis at some concentrations and promoting PIN2 degradation at others. However, how PIN proteins are turned over in plant cells is yet to be addressed.

Methodology and principle findings: Using laser confocal scanning microscopy, and physiological and molecular genetic approaches, here, we show that in dark-grown seedlings, the PM localization of auxin efflux carrier PIN2 was largely reduced, and, in addition, PIN2 signal was detected in vacuolar compartments. This is in contrast to light-grown seedlings where PIN2 was predominantly PM-localized. In light-grown plants after shift to dark or to continuous red or far-red light, PIN2 also accumulated in vacuolar compartments. We show that PIN2 vacuolar targeting was derived from the PM via endocytic trafficking and inhibited by HY5-dependent light signaling. In addition, the ubiquitin 26S proteasome is involved in the process, since its inhibition by mutations in COP9 and a proteasome inhibitor MG132 impaired the process.

Conclusions and significance: Collectively, our data indicate that light plays an essential role in PIN2 intracellular trafficking, promoting PM-localization in the presence of light and, on the other hand, vacuolar targeting for protein degradation in the absence of light. Based on these results, we postulate that light regulation of root development is mediated at least in part by changes in the intracellular distribution of auxin efflux carriers, PIN proteins, in response to the light environment.

Show MeSH
Related in: MedlinePlus