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Dual targeting and retrograde translocation: regulators of plant nuclear gene expression can be sequestered by plastids.

Krause K, Oetke S, Krupinska K - Int J Mol Sci (2012)

Bottom Line: Indeed, several proteins exhibiting a dual localization in the plastids and the nucleus are promising candidates for such a direct signal transduction involving regulatory protein storage in the plastids.Among such proteins, the nuclear transcription factor WHIRLY1 stands out as being the only protein for which an export from plastids and translocation to the nucleus has been experimentally demonstrated.Other proteins, however, strongly support the notion that this pathway might be more common than currently believed.

View Article: PubMed Central - PubMed

Affiliation: Department of Arctic and Marine Biology, University of Tromsø, Tromsø 9037, Norway; E-Mail: kirsten.krause@uit.no.

ABSTRACT
Changes in the developmental or metabolic state of plastids can trigger profound changes in the transcript profiles of nuclear genes. Many nuclear transcription factors were shown to be controlled by signals generated in the organelles. In addition to the many different compounds for which an involvement in retrograde signaling is discussed, accumulating evidence suggests a role for proteins in plastid-to-nucleus communication. These proteins might be sequestered in the plastids before they act as transcriptional regulators in the nucleus. Indeed, several proteins exhibiting a dual localization in the plastids and the nucleus are promising candidates for such a direct signal transduction involving regulatory protein storage in the plastids. Among such proteins, the nuclear transcription factor WHIRLY1 stands out as being the only protein for which an export from plastids and translocation to the nucleus has been experimentally demonstrated. Other proteins, however, strongly support the notion that this pathway might be more common than currently believed.

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Related in: MedlinePlus

Selected mechanisms of protein translocation from chloroplasts to the nucleus. (A) Putative ER mediated transfer of plastid proteins to the nucleus. A periplasmic space formed by ER cisternae and intermembrane space of plastids has been observed under certain conditions (see text). Proteins from the stroma of plastids would need to transverse a single membrane to become included in this space, which is continuous with the envelope of nuclei. To enter the nucleus, proteins would need to cross the inner membrane of the nuclear envelope; (B) Hypothetical release of proteins directly into the cytoplasm. Transient pores might be formed by activity of proteins such as TGD2 being involved in lipid exchange between ER and plastids [90]. Small disruptions in the membrane leading to a leakiness of chloroplasts might occur upon stress. Black dots, released plastidic proteins; red ellipse, protein complex which mediates membrane permeability; NE, nuclear envelope; ER, endoplasmic reticulum; IM, inner membrane; OM, outer membrane.
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f2-ijms-13-11085: Selected mechanisms of protein translocation from chloroplasts to the nucleus. (A) Putative ER mediated transfer of plastid proteins to the nucleus. A periplasmic space formed by ER cisternae and intermembrane space of plastids has been observed under certain conditions (see text). Proteins from the stroma of plastids would need to transverse a single membrane to become included in this space, which is continuous with the envelope of nuclei. To enter the nucleus, proteins would need to cross the inner membrane of the nuclear envelope; (B) Hypothetical release of proteins directly into the cytoplasm. Transient pores might be formed by activity of proteins such as TGD2 being involved in lipid exchange between ER and plastids [90]. Small disruptions in the membrane leading to a leakiness of chloroplasts might occur upon stress. Black dots, released plastidic proteins; red ellipse, protein complex which mediates membrane permeability; NE, nuclear envelope; ER, endoplasmic reticulum; IM, inner membrane; OM, outer membrane.

Mentions: At certain stages of chloroplast development, ER cisternae were found to form a sheath around plastids and the membranes even became continuous with the outer envelope membrane of plastids [76,77] (see Figure 2A). It is not unlikely that vesicles can be formed from such an ER-like periplastic space. Such vesicles would consist of only one surrounding membrane (Figure 2A) and would thereby differ from the vesicles formed by tip shedding of stromules. Vesicles surrounded by a single envelope membrane are a common form of communication for both bacteria and mitochondria [78,79]. In bacteria, vesicles can include proteins, toxins and DNA [80]. Protein export by vesicles was also observed in the symbiotically living cyanobacterium Azolla microphylla where such vesicles are released into the extracellular space [81]. Mitochondria derived vesicles were shown to contain specific cargo proteins indicating a selectivity of protein sorting into vesicles [82].


Dual targeting and retrograde translocation: regulators of plant nuclear gene expression can be sequestered by plastids.

Krause K, Oetke S, Krupinska K - Int J Mol Sci (2012)

Selected mechanisms of protein translocation from chloroplasts to the nucleus. (A) Putative ER mediated transfer of plastid proteins to the nucleus. A periplasmic space formed by ER cisternae and intermembrane space of plastids has been observed under certain conditions (see text). Proteins from the stroma of plastids would need to transverse a single membrane to become included in this space, which is continuous with the envelope of nuclei. To enter the nucleus, proteins would need to cross the inner membrane of the nuclear envelope; (B) Hypothetical release of proteins directly into the cytoplasm. Transient pores might be formed by activity of proteins such as TGD2 being involved in lipid exchange between ER and plastids [90]. Small disruptions in the membrane leading to a leakiness of chloroplasts might occur upon stress. Black dots, released plastidic proteins; red ellipse, protein complex which mediates membrane permeability; NE, nuclear envelope; ER, endoplasmic reticulum; IM, inner membrane; OM, outer membrane.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3472732&req=5

f2-ijms-13-11085: Selected mechanisms of protein translocation from chloroplasts to the nucleus. (A) Putative ER mediated transfer of plastid proteins to the nucleus. A periplasmic space formed by ER cisternae and intermembrane space of plastids has been observed under certain conditions (see text). Proteins from the stroma of plastids would need to transverse a single membrane to become included in this space, which is continuous with the envelope of nuclei. To enter the nucleus, proteins would need to cross the inner membrane of the nuclear envelope; (B) Hypothetical release of proteins directly into the cytoplasm. Transient pores might be formed by activity of proteins such as TGD2 being involved in lipid exchange between ER and plastids [90]. Small disruptions in the membrane leading to a leakiness of chloroplasts might occur upon stress. Black dots, released plastidic proteins; red ellipse, protein complex which mediates membrane permeability; NE, nuclear envelope; ER, endoplasmic reticulum; IM, inner membrane; OM, outer membrane.
Mentions: At certain stages of chloroplast development, ER cisternae were found to form a sheath around plastids and the membranes even became continuous with the outer envelope membrane of plastids [76,77] (see Figure 2A). It is not unlikely that vesicles can be formed from such an ER-like periplastic space. Such vesicles would consist of only one surrounding membrane (Figure 2A) and would thereby differ from the vesicles formed by tip shedding of stromules. Vesicles surrounded by a single envelope membrane are a common form of communication for both bacteria and mitochondria [78,79]. In bacteria, vesicles can include proteins, toxins and DNA [80]. Protein export by vesicles was also observed in the symbiotically living cyanobacterium Azolla microphylla where such vesicles are released into the extracellular space [81]. Mitochondria derived vesicles were shown to contain specific cargo proteins indicating a selectivity of protein sorting into vesicles [82].

Bottom Line: Indeed, several proteins exhibiting a dual localization in the plastids and the nucleus are promising candidates for such a direct signal transduction involving regulatory protein storage in the plastids.Among such proteins, the nuclear transcription factor WHIRLY1 stands out as being the only protein for which an export from plastids and translocation to the nucleus has been experimentally demonstrated.Other proteins, however, strongly support the notion that this pathway might be more common than currently believed.

View Article: PubMed Central - PubMed

Affiliation: Department of Arctic and Marine Biology, University of Tromsø, Tromsø 9037, Norway; E-Mail: kirsten.krause@uit.no.

ABSTRACT
Changes in the developmental or metabolic state of plastids can trigger profound changes in the transcript profiles of nuclear genes. Many nuclear transcription factors were shown to be controlled by signals generated in the organelles. In addition to the many different compounds for which an involvement in retrograde signaling is discussed, accumulating evidence suggests a role for proteins in plastid-to-nucleus communication. These proteins might be sequestered in the plastids before they act as transcriptional regulators in the nucleus. Indeed, several proteins exhibiting a dual localization in the plastids and the nucleus are promising candidates for such a direct signal transduction involving regulatory protein storage in the plastids. Among such proteins, the nuclear transcription factor WHIRLY1 stands out as being the only protein for which an export from plastids and translocation to the nucleus has been experimentally demonstrated. Other proteins, however, strongly support the notion that this pathway might be more common than currently believed.

Show MeSH
Related in: MedlinePlus