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Growth attenuation under saline stress is mediated by the heterotrimeric G protein complex.

Colaneri AC, Tunc-Ozdemir M, Huang JP, Jones AM - BMC Plant Biol. (2014)

Bottom Line: Glucose in the growth media improved the survival under salt stress in Col but not in agb1-2 or rgs1-2 mutants.These results demonstrate a direct role for G-protein signaling in the plant growth response to salt stress.The phenotypes of the loss-of-function mutations prompted the model that during salt stress, G activation promotes growth and attenuates senescence probably by releasing ER stress.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill NC, 27599, USA. alan_jones@unc.edu.

ABSTRACT

Background: Plant growth is plastic, able to rapidly adjust to fluctuation in environmental conditions such as drought and salinity. Due to long-term irrigation use in agricultural systems, soil salinity is increasing; consequently crop yield is adversely affected. It is known that salt tolerance is a quantitative trait supported by genes affecting ion homeostasis, ion transport, ion compartmentalization and ion selectivity. Less is known about pathways connecting NaCl and cell proliferation and cell death. Plant growth and cell proliferation is, in part, controlled by the concerted activity of the heterotrimeric G-protein complex with glucose. Prompted by the abundance of stress-related, functional annotations of genes encoding proteins that interact with core components of the Arabidopsis heterotrimeric G protein complex (AtRGS1, AtGPA1, AGB1, and AGG), we tested the hypothesis that G proteins modulate plant growth under salt stress.

Results: Na+ activates G signaling as quantitated by internalization of Arabidopsis Regulator of G Signaling protein 1 (AtRGS1). Despite being components of a singular signaling complex loss of the Gβ subunit (agb1-2 mutant) conferred accelerated senescence and aborted development in the presence of Na+, whereas loss of AtRGS1 (rgs1-2 mutant) conferred Na+ tolerance evident as less attenuated shoot growth and senescence. Site-directed changes in the Gα and Gβγ protein-protein interface were made to disrupt the interaction between the Gα and Gβγ subunits in order to elevate free activated Gα subunit and free Gβγ dimer at the plasma membrane. These mutations conferred sodium tolerance. Glucose in the growth media improved the survival under salt stress in Col but not in agb1-2 or rgs1-2 mutants.

Conclusions: These results demonstrate a direct role for G-protein signaling in the plant growth response to salt stress. The contrasting phenotypes of agb1-2 and rgs1-2 mutants suggest that G-proteins balance growth and death under salt stress. The phenotypes of the loss-of-function mutations prompted the model that during salt stress, G activation promotes growth and attenuates senescence probably by releasing ER stress.

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Na+ triggers AtRGS1–YFP endocytosis. A) 5-d-old agb1-2 and Col-0 seedlings that were grown on ¼ MS agar plates were then transplanted to ¼ MS agar plates supplemented with 200 mM NaCl. Images were captured over time, but shown are seedlings 5 d after initiation of the treatment (i.e. 10-d-old). B) AtRGS1–YFP endocytosis in Arabidopsis hypocotyl epidermal cells after treatment with various concentrations of NaCl or KCl for 16 h. Differential interference contrast (DIC) shows no change in cell integrity after 16 h of 100 mM NaCl treatment. The DIC is image of the same hypocotyl shown for the 100 mM NaCl treatment. C) AtRGS1 internalization was quantified after 16 h treatment at the indicated NaCl concentrations. CHX: seedlings were incubated with 70 μm cyclohexamide followed by water (control) or 50 mM NaCl treatment for 16 h. Error bars represent standard deviation, n = replicates. Pair wise comparisons between the means were performed with a T-test confidence level (CL) of 95%. All pair-wise comparisons included their respective control (no salt). *, means (treatment and control) differ significantly (p value < 0.05). Scale bars = 10 μm.
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Figure 1: Na+ triggers AtRGS1–YFP endocytosis. A) 5-d-old agb1-2 and Col-0 seedlings that were grown on ¼ MS agar plates were then transplanted to ¼ MS agar plates supplemented with 200 mM NaCl. Images were captured over time, but shown are seedlings 5 d after initiation of the treatment (i.e. 10-d-old). B) AtRGS1–YFP endocytosis in Arabidopsis hypocotyl epidermal cells after treatment with various concentrations of NaCl or KCl for 16 h. Differential interference contrast (DIC) shows no change in cell integrity after 16 h of 100 mM NaCl treatment. The DIC is image of the same hypocotyl shown for the 100 mM NaCl treatment. C) AtRGS1 internalization was quantified after 16 h treatment at the indicated NaCl concentrations. CHX: seedlings were incubated with 70 μm cyclohexamide followed by water (control) or 50 mM NaCl treatment for 16 h. Error bars represent standard deviation, n = replicates. Pair wise comparisons between the means were performed with a T-test confidence level (CL) of 95%. All pair-wise comparisons included their respective control (no salt). *, means (treatment and control) differ significantly (p value < 0.05). Scale bars = 10 μm.

Mentions: Our functional profile analysis for the G-protein interactome suggested that G proteins mediate NaCl responses. To test this hypothesis, we transplanted 5-d-old Arabidopsis seedlings of the different genotypes from ¼ MS agar plates to ¼ MS agar plates supplemented with 200 mM NaCl. Arabidopsis seedlings lacking the Gβ subunit of the heterotrimeric G protein complex (agb1-2) rapidly senesced (Figure 1A) compared to the wild-type. agb1-2 seedlings became bleached of chlorophyll while Col-0 seedlings displayed typical stress symptoms such as high levels of anthocyanin (Figure 1A) but did not bleach. This prompted the hypothesis that NaCl itself directly or indirectly activates G signaling to promote stress survival. To test activation, plants expressing AtRGS1-YFP were treated with NaCl or KCl and AtRGS1-YFP internalization was quantitated. AtRGS1 internalization is a standard reporter for G protein activation [28]. NaCl, but not KCl, initiated G signaling indicating activation is caused by Na+ not Cl− (Figure 1B and C). Proteins visualized in the endosome after NaCl treatment had a plasma membrane origin since blocking new synthesis of protein had no effect on the subcellular location after treatment (Figure 1C).


Growth attenuation under saline stress is mediated by the heterotrimeric G protein complex.

Colaneri AC, Tunc-Ozdemir M, Huang JP, Jones AM - BMC Plant Biol. (2014)

Na+ triggers AtRGS1–YFP endocytosis. A) 5-d-old agb1-2 and Col-0 seedlings that were grown on ¼ MS agar plates were then transplanted to ¼ MS agar plates supplemented with 200 mM NaCl. Images were captured over time, but shown are seedlings 5 d after initiation of the treatment (i.e. 10-d-old). B) AtRGS1–YFP endocytosis in Arabidopsis hypocotyl epidermal cells after treatment with various concentrations of NaCl or KCl for 16 h. Differential interference contrast (DIC) shows no change in cell integrity after 16 h of 100 mM NaCl treatment. The DIC is image of the same hypocotyl shown for the 100 mM NaCl treatment. C) AtRGS1 internalization was quantified after 16 h treatment at the indicated NaCl concentrations. CHX: seedlings were incubated with 70 μm cyclohexamide followed by water (control) or 50 mM NaCl treatment for 16 h. Error bars represent standard deviation, n = replicates. Pair wise comparisons between the means were performed with a T-test confidence level (CL) of 95%. All pair-wise comparisons included their respective control (no salt). *, means (treatment and control) differ significantly (p value < 0.05). Scale bars = 10 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 1: Na+ triggers AtRGS1–YFP endocytosis. A) 5-d-old agb1-2 and Col-0 seedlings that were grown on ¼ MS agar plates were then transplanted to ¼ MS agar plates supplemented with 200 mM NaCl. Images were captured over time, but shown are seedlings 5 d after initiation of the treatment (i.e. 10-d-old). B) AtRGS1–YFP endocytosis in Arabidopsis hypocotyl epidermal cells after treatment with various concentrations of NaCl or KCl for 16 h. Differential interference contrast (DIC) shows no change in cell integrity after 16 h of 100 mM NaCl treatment. The DIC is image of the same hypocotyl shown for the 100 mM NaCl treatment. C) AtRGS1 internalization was quantified after 16 h treatment at the indicated NaCl concentrations. CHX: seedlings were incubated with 70 μm cyclohexamide followed by water (control) or 50 mM NaCl treatment for 16 h. Error bars represent standard deviation, n = replicates. Pair wise comparisons between the means were performed with a T-test confidence level (CL) of 95%. All pair-wise comparisons included their respective control (no salt). *, means (treatment and control) differ significantly (p value < 0.05). Scale bars = 10 μm.
Mentions: Our functional profile analysis for the G-protein interactome suggested that G proteins mediate NaCl responses. To test this hypothesis, we transplanted 5-d-old Arabidopsis seedlings of the different genotypes from ¼ MS agar plates to ¼ MS agar plates supplemented with 200 mM NaCl. Arabidopsis seedlings lacking the Gβ subunit of the heterotrimeric G protein complex (agb1-2) rapidly senesced (Figure 1A) compared to the wild-type. agb1-2 seedlings became bleached of chlorophyll while Col-0 seedlings displayed typical stress symptoms such as high levels of anthocyanin (Figure 1A) but did not bleach. This prompted the hypothesis that NaCl itself directly or indirectly activates G signaling to promote stress survival. To test activation, plants expressing AtRGS1-YFP were treated with NaCl or KCl and AtRGS1-YFP internalization was quantitated. AtRGS1 internalization is a standard reporter for G protein activation [28]. NaCl, but not KCl, initiated G signaling indicating activation is caused by Na+ not Cl− (Figure 1B and C). Proteins visualized in the endosome after NaCl treatment had a plasma membrane origin since blocking new synthesis of protein had no effect on the subcellular location after treatment (Figure 1C).

Bottom Line: Glucose in the growth media improved the survival under salt stress in Col but not in agb1-2 or rgs1-2 mutants.These results demonstrate a direct role for G-protein signaling in the plant growth response to salt stress.The phenotypes of the loss-of-function mutations prompted the model that during salt stress, G activation promotes growth and attenuates senescence probably by releasing ER stress.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill NC, 27599, USA. alan_jones@unc.edu.

ABSTRACT

Background: Plant growth is plastic, able to rapidly adjust to fluctuation in environmental conditions such as drought and salinity. Due to long-term irrigation use in agricultural systems, soil salinity is increasing; consequently crop yield is adversely affected. It is known that salt tolerance is a quantitative trait supported by genes affecting ion homeostasis, ion transport, ion compartmentalization and ion selectivity. Less is known about pathways connecting NaCl and cell proliferation and cell death. Plant growth and cell proliferation is, in part, controlled by the concerted activity of the heterotrimeric G-protein complex with glucose. Prompted by the abundance of stress-related, functional annotations of genes encoding proteins that interact with core components of the Arabidopsis heterotrimeric G protein complex (AtRGS1, AtGPA1, AGB1, and AGG), we tested the hypothesis that G proteins modulate plant growth under salt stress.

Results: Na+ activates G signaling as quantitated by internalization of Arabidopsis Regulator of G Signaling protein 1 (AtRGS1). Despite being components of a singular signaling complex loss of the Gβ subunit (agb1-2 mutant) conferred accelerated senescence and aborted development in the presence of Na+, whereas loss of AtRGS1 (rgs1-2 mutant) conferred Na+ tolerance evident as less attenuated shoot growth and senescence. Site-directed changes in the Gα and Gβγ protein-protein interface were made to disrupt the interaction between the Gα and Gβγ subunits in order to elevate free activated Gα subunit and free Gβγ dimer at the plasma membrane. These mutations conferred sodium tolerance. Glucose in the growth media improved the survival under salt stress in Col but not in agb1-2 or rgs1-2 mutants.

Conclusions: These results demonstrate a direct role for G-protein signaling in the plant growth response to salt stress. The contrasting phenotypes of agb1-2 and rgs1-2 mutants suggest that G-proteins balance growth and death under salt stress. The phenotypes of the loss-of-function mutations prompted the model that during salt stress, G activation promotes growth and attenuates senescence probably by releasing ER stress.

Show MeSH
Related in: MedlinePlus