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A loss-of-function mutation in the nucleoporin AtNUP160 indicates that normal auxin signalling is required for a proper ethylene response in Arabidopsis.

Robles LM, Deslauriers SD, Alvarez AA, Larsen PB - J. Exp. Bot. (2012)

Bottom Line: It was subsequently determined by map-based cloning that the mutant (sar1-7) represents a loss-of-function mutation in the previously described nucleoporin AtNUP160 (At1g33410, SAR1).In support of previously reported results, the sar1-7 mutant partially restored auxin responsiveness to roots of an rce1 loss-of-function mutant, indicating that AtNUP160/SAR1 is required for proper expression of factors responsible for the repression of auxin signalling.Consistent with this, addition of auxin to ethylene-treated seedlings resulted in severe hypocotyl shortening, reminiscent of that seen for other eer (enhanced ethylene response) mutants, suggesting that auxin functions in part synergistically with ethylene to control hypocotyl elongation and other ethylene-dependent phenomena.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, University of California-Riverside, Riverside, CA 92521, USA.

ABSTRACT
As part of a continuing effort to elucidate mechanisms that regulate the magnitude of ethylene signalling, an Arabidopsis mutant with an enhanced ethylene response was identified. Subsequent characterization of this loss-of-function mutant revealed severe hypocotyl shortening in the presence of saturating ethylene along with increased expression in leaves of a subset of ethylene-responsive genes. It was subsequently determined by map-based cloning that the mutant (sar1-7) represents a loss-of-function mutation in the previously described nucleoporin AtNUP160 (At1g33410, SAR1). In support of previously reported results, the sar1-7 mutant partially restored auxin responsiveness to roots of an rce1 loss-of-function mutant, indicating that AtNUP160/SAR1 is required for proper expression of factors responsible for the repression of auxin signalling. Analysis of arf7-1/sar1-7 and arf19-1/sar1-7 double mutants revealed that mutations affecting either ARF7 or ARF19 function almost fully blocked manifestation of the sar1-7-dependent ethylene hypersensitivity phenotype, suggesting that ARF7- and ARF19-mediated auxin signalling is responsible for regulating the magnitude of and/or competence for the ethylene response in Arabidopsis etiolated hypocotyls. Consistent with this, addition of auxin to ethylene-treated seedlings resulted in severe hypocotyl shortening, reminiscent of that seen for other eer (enhanced ethylene response) mutants, suggesting that auxin functions in part synergistically with ethylene to control hypocotyl elongation and other ethylene-dependent phenomena.

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Auxin signalling controls the magnitude of and competence for the ethylene response. (A–C) Wild-type seedlings were grown in the dark for 4 d with 5 μM AgNO3 or 100 μl l−1 ethylene supplemented with 0, 50 (A,), or 500 nM (B, C) IAA, after which hypocotyl length was determined for each treatment. (D) Col-0 wt seedlings were grown for 7 d hydroponically, after which all samples were treated with 10 μM (+/–)-JA for 24 h either in the absence (A) or presence (E) of 10 μM ACC. As part of this treatment, sample pairs (i.e. control and +ACC) were additionally supplemented with 1 μM IAA for the final 8 h of the ACC treatment and compared with a control pair that was treated with ethanol only. Following this, whole seedlings were collected and total RNA was isolated for Northern blot analysis for PDF1.2. (E) Wild-type seedlings were grown for 4 d in the dark with 100 μl l−1 ethylene supplemented with either 0 or 50 μM PCIB, an auxin-response inhibitor. (F) Wild-type and sar1-7 etiolated seedings were grown for 4 d in the presence of 100 μl l−1 ethylene supplemented with 0, 5, or 10 μM PCIB after which hypocotyl length was measured.
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fig7: Auxin signalling controls the magnitude of and competence for the ethylene response. (A–C) Wild-type seedlings were grown in the dark for 4 d with 5 μM AgNO3 or 100 μl l−1 ethylene supplemented with 0, 50 (A,), or 500 nM (B, C) IAA, after which hypocotyl length was determined for each treatment. (D) Col-0 wt seedlings were grown for 7 d hydroponically, after which all samples were treated with 10 μM (+/–)-JA for 24 h either in the absence (A) or presence (E) of 10 μM ACC. As part of this treatment, sample pairs (i.e. control and +ACC) were additionally supplemented with 1 μM IAA for the final 8 h of the ACC treatment and compared with a control pair that was treated with ethanol only. Following this, whole seedlings were collected and total RNA was isolated for Northern blot analysis for PDF1.2. (E) Wild-type seedlings were grown for 4 d in the dark with 100 μl l−1 ethylene supplemented with either 0 or 50 μM PCIB, an auxin-response inhibitor. (F) Wild-type and sar1-7 etiolated seedings were grown for 4 d in the presence of 100 μl l−1 ethylene supplemented with 0, 5, or 10 μM PCIB after which hypocotyl length was measured.

Mentions: Based on the reported role of SAR1 in regulation of the auxin response coupled with our observations regarding sar1 loss-of-function mutants having ethylene hypersensitivity, we hypothesized that auxin plays a synergistic role with regard to modulating the level of the ethylene response in Arabidopsis. To test this, etiolated wt Arabidopsis seedlings were grown in the presence of 5 μM AgNO3 or 100 μl l−1 ethylene with or without 50 or 500 nM IAA for 4 d. As shown in Fig. 7A–C, whereas there was only a slight difference in hypocotyl length when comparing the AgNO3 control with AgNO3+IAA, there was a severe reduction in hypocotyl length for seedlings treated with both saturating ethylene and IAA compared with treatment with ethylene alone. The phenotype of seedlings that were treated with a combination of saturating ethylene and IAA was indistinguishable from the phenotypes of several published eer mutants including eer1/rcn1, eer3, and eer5 (Larsen and Cancel, 2003; Christians and Larsen, 2007; Robles et al., 2007; Christians et al., 2008).


A loss-of-function mutation in the nucleoporin AtNUP160 indicates that normal auxin signalling is required for a proper ethylene response in Arabidopsis.

Robles LM, Deslauriers SD, Alvarez AA, Larsen PB - J. Exp. Bot. (2012)

Auxin signalling controls the magnitude of and competence for the ethylene response. (A–C) Wild-type seedlings were grown in the dark for 4 d with 5 μM AgNO3 or 100 μl l−1 ethylene supplemented with 0, 50 (A,), or 500 nM (B, C) IAA, after which hypocotyl length was determined for each treatment. (D) Col-0 wt seedlings were grown for 7 d hydroponically, after which all samples were treated with 10 μM (+/–)-JA for 24 h either in the absence (A) or presence (E) of 10 μM ACC. As part of this treatment, sample pairs (i.e. control and +ACC) were additionally supplemented with 1 μM IAA for the final 8 h of the ACC treatment and compared with a control pair that was treated with ethanol only. Following this, whole seedlings were collected and total RNA was isolated for Northern blot analysis for PDF1.2. (E) Wild-type seedlings were grown for 4 d in the dark with 100 μl l−1 ethylene supplemented with either 0 or 50 μM PCIB, an auxin-response inhibitor. (F) Wild-type and sar1-7 etiolated seedings were grown for 4 d in the presence of 100 μl l−1 ethylene supplemented with 0, 5, or 10 μM PCIB after which hypocotyl length was measured.
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fig7: Auxin signalling controls the magnitude of and competence for the ethylene response. (A–C) Wild-type seedlings were grown in the dark for 4 d with 5 μM AgNO3 or 100 μl l−1 ethylene supplemented with 0, 50 (A,), or 500 nM (B, C) IAA, after which hypocotyl length was determined for each treatment. (D) Col-0 wt seedlings were grown for 7 d hydroponically, after which all samples were treated with 10 μM (+/–)-JA for 24 h either in the absence (A) or presence (E) of 10 μM ACC. As part of this treatment, sample pairs (i.e. control and +ACC) were additionally supplemented with 1 μM IAA for the final 8 h of the ACC treatment and compared with a control pair that was treated with ethanol only. Following this, whole seedlings were collected and total RNA was isolated for Northern blot analysis for PDF1.2. (E) Wild-type seedlings were grown for 4 d in the dark with 100 μl l−1 ethylene supplemented with either 0 or 50 μM PCIB, an auxin-response inhibitor. (F) Wild-type and sar1-7 etiolated seedings were grown for 4 d in the presence of 100 μl l−1 ethylene supplemented with 0, 5, or 10 μM PCIB after which hypocotyl length was measured.
Mentions: Based on the reported role of SAR1 in regulation of the auxin response coupled with our observations regarding sar1 loss-of-function mutants having ethylene hypersensitivity, we hypothesized that auxin plays a synergistic role with regard to modulating the level of the ethylene response in Arabidopsis. To test this, etiolated wt Arabidopsis seedlings were grown in the presence of 5 μM AgNO3 or 100 μl l−1 ethylene with or without 50 or 500 nM IAA for 4 d. As shown in Fig. 7A–C, whereas there was only a slight difference in hypocotyl length when comparing the AgNO3 control with AgNO3+IAA, there was a severe reduction in hypocotyl length for seedlings treated with both saturating ethylene and IAA compared with treatment with ethylene alone. The phenotype of seedlings that were treated with a combination of saturating ethylene and IAA was indistinguishable from the phenotypes of several published eer mutants including eer1/rcn1, eer3, and eer5 (Larsen and Cancel, 2003; Christians and Larsen, 2007; Robles et al., 2007; Christians et al., 2008).

Bottom Line: It was subsequently determined by map-based cloning that the mutant (sar1-7) represents a loss-of-function mutation in the previously described nucleoporin AtNUP160 (At1g33410, SAR1).In support of previously reported results, the sar1-7 mutant partially restored auxin responsiveness to roots of an rce1 loss-of-function mutant, indicating that AtNUP160/SAR1 is required for proper expression of factors responsible for the repression of auxin signalling.Consistent with this, addition of auxin to ethylene-treated seedlings resulted in severe hypocotyl shortening, reminiscent of that seen for other eer (enhanced ethylene response) mutants, suggesting that auxin functions in part synergistically with ethylene to control hypocotyl elongation and other ethylene-dependent phenomena.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, University of California-Riverside, Riverside, CA 92521, USA.

ABSTRACT
As part of a continuing effort to elucidate mechanisms that regulate the magnitude of ethylene signalling, an Arabidopsis mutant with an enhanced ethylene response was identified. Subsequent characterization of this loss-of-function mutant revealed severe hypocotyl shortening in the presence of saturating ethylene along with increased expression in leaves of a subset of ethylene-responsive genes. It was subsequently determined by map-based cloning that the mutant (sar1-7) represents a loss-of-function mutation in the previously described nucleoporin AtNUP160 (At1g33410, SAR1). In support of previously reported results, the sar1-7 mutant partially restored auxin responsiveness to roots of an rce1 loss-of-function mutant, indicating that AtNUP160/SAR1 is required for proper expression of factors responsible for the repression of auxin signalling. Analysis of arf7-1/sar1-7 and arf19-1/sar1-7 double mutants revealed that mutations affecting either ARF7 or ARF19 function almost fully blocked manifestation of the sar1-7-dependent ethylene hypersensitivity phenotype, suggesting that ARF7- and ARF19-mediated auxin signalling is responsible for regulating the magnitude of and/or competence for the ethylene response in Arabidopsis etiolated hypocotyls. Consistent with this, addition of auxin to ethylene-treated seedlings resulted in severe hypocotyl shortening, reminiscent of that seen for other eer (enhanced ethylene response) mutants, suggesting that auxin functions in part synergistically with ethylene to control hypocotyl elongation and other ethylene-dependent phenomena.

Show MeSH
Related in: MedlinePlus