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Sl-IAA3, a tomato Aux/IAA at the crossroads of auxin and ethylene signalling involved in differential growth.

Chaabouni S, Jones B, Delalande C, Wang H, Li Z, Mila I, Frasse P, Latché A, Pech JC, Bouzayen M - J. Exp. Bot. (2009)

Bottom Line: Sl-IAA3 expression is auxin and ethylene dependent, is regulated on a tight tissue-specific basis, and is associated with tissues undergoing differential growth such as in epinastic petioles and apical hook.Antisense down-regulation of Sl-IAA3 results in auxin and ethylene-related phenotypes, including altered apical dominance, lower auxin sensitivity, exaggerated apical hook curvature in the dark and reduced petiole epinasty in the light.The results provide novel insights into the roles of Aux/IAAs and position the Sl-IAA3 protein at the crossroads of auxin and ethylene signalling in tomato.

View Article: PubMed Central - PubMed

Affiliation: Université de Toulouse, INP-ENSA Toulouse, Génomique et Biotechnologie des Fruits, Avenue de l'Agrobiopole BP 32607, Castanet-Tolosan F-31326, France.

ABSTRACT
Whereas the interplay of multiple hormones is essential for most plant developmental processes, the key integrating molecular players remain largely undiscovered or uncharacterized. It is shown here that a member of the tomato auxin/indole-3-acetic acid (Aux/IAA) gene family, Sl-IAA3, intersects the auxin and ethylene signal transduction pathways. Aux/IAA genes encode short-lived transcriptional regulators central to the control of auxin responses. Their functions have been defined primarily by dominant, gain-of-function mutant alleles in Arabidopsis. The Sl-IAA3 gene encodes a nuclear-targeted protein that can repress transcription from auxin-responsive promoters. Sl-IAA3 expression is auxin and ethylene dependent, is regulated on a tight tissue-specific basis, and is associated with tissues undergoing differential growth such as in epinastic petioles and apical hook. Antisense down-regulation of Sl-IAA3 results in auxin and ethylene-related phenotypes, including altered apical dominance, lower auxin sensitivity, exaggerated apical hook curvature in the dark and reduced petiole epinasty in the light. The results provide novel insights into the roles of Aux/IAAs and position the Sl-IAA3 protein at the crossroads of auxin and ethylene signalling in tomato.

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Auxin responsiveness of the Sl-IAA3 gene. (A) qRT-PCR analysis of Sl-IAA3 transcript levels in 3-week-old light-grown control and auxin-treated (20 μM IAA for 2 h) seedlings in presence or absence of 1 μl l−11-MCP applied 16 h prior to auxin treatment. Relative expression level on the y-axis refers to the fold difference in SI-IAA3 transcript levels relative to the non-treated plantlets. (B) Auxin responsiveness of the Sl-IAA3 promoter. Tobacco protoplasts were transformed by PIAA3::GFP and incubated in the presence or absence of 2,4-D (50 μM). Transformation was performed in triplicate and, in each experiment, GFP fluorescence was measured by flow cytometry 16 h after transfection. Values are expressed in arbitrary units (a.u.) ±standard error. (C–F) Tissue-specific expression of Sl-IAA3 assessed in transgenic tomato expressing GUS reporter gene driven by the Sl-IAA3 promoter (PIAA3::GUS). The expression pattern was analysed in 3-week-old seedlings (C), leaves (D), roots (E), and MG fruit (F). (G–J) These images correspond to the same tissues treated for 2 h with 20 μM IAA. (K–N) These images correspond to the same tissues expressing the DR5 auxin-responsive promoter fused to the GUS reporter gene (DR5::GUS) and those in (O–R) to DR5::GUS treated with 20 μM IAA. The data are representative of at least three independent experiments with n > 20 seedlings examined per experiment.
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fig3: Auxin responsiveness of the Sl-IAA3 gene. (A) qRT-PCR analysis of Sl-IAA3 transcript levels in 3-week-old light-grown control and auxin-treated (20 μM IAA for 2 h) seedlings in presence or absence of 1 μl l−11-MCP applied 16 h prior to auxin treatment. Relative expression level on the y-axis refers to the fold difference in SI-IAA3 transcript levels relative to the non-treated plantlets. (B) Auxin responsiveness of the Sl-IAA3 promoter. Tobacco protoplasts were transformed by PIAA3::GFP and incubated in the presence or absence of 2,4-D (50 μM). Transformation was performed in triplicate and, in each experiment, GFP fluorescence was measured by flow cytometry 16 h after transfection. Values are expressed in arbitrary units (a.u.) ±standard error. (C–F) Tissue-specific expression of Sl-IAA3 assessed in transgenic tomato expressing GUS reporter gene driven by the Sl-IAA3 promoter (PIAA3::GUS). The expression pattern was analysed in 3-week-old seedlings (C), leaves (D), roots (E), and MG fruit (F). (G–J) These images correspond to the same tissues treated for 2 h with 20 μM IAA. (K–N) These images correspond to the same tissues expressing the DR5 auxin-responsive promoter fused to the GUS reporter gene (DR5::GUS) and those in (O–R) to DR5::GUS treated with 20 μM IAA. The data are representative of at least three independent experiments with n > 20 seedlings examined per experiment.

Mentions: In dark-grown seedlings, qRT-PCR analysis revealed that ethylene induction of Sl-IAA3 transcript accumulation mimicked both the dose-response and the time-course gradient of the well-characterized ethylene-responsive gene, E8 (see Fig. S1 in Supplementary data available at JXB online). Sl-IAA3 transcript levels also increased 4-fold in light-grown tomato seedlings after 2 h of auxin (20 μM IAA) treatment (Fig. 3A). In tobacco BY2 protoplasts transfection assays, Sl-IAA3 promoter (1668 bp)-driven GFP levels increased 4-fold after auxin treatment (50 μM 2,4-D) (Fig. 3B). As auxin is known to stimulate ethylene production (Abel et al., 1995), it was decided to determine whether this auxin-responsiveness resulted from an increase in ethylene production. Light-grown tomato seedlings were treated overnight with 1-MCP (1μl l−1) and then incubated in presence or absence of auxin. Similarly to the observation in fruit, 1-MCP almost completely abolished SI-IAA3 transcripts in untreated tomato seedlings (Fig. 3A). In the presence of both 1-MCP and auxin, however, Sl-IAA3 transcript levels were only partially reduced (Fig. 3A), indicating that in light-grown tomato seedlings SI-IAA3 is both auxin and ethylene-inducible and that the auxin-responsiveness is partially mediated by ethylene.


Sl-IAA3, a tomato Aux/IAA at the crossroads of auxin and ethylene signalling involved in differential growth.

Chaabouni S, Jones B, Delalande C, Wang H, Li Z, Mila I, Frasse P, Latché A, Pech JC, Bouzayen M - J. Exp. Bot. (2009)

Auxin responsiveness of the Sl-IAA3 gene. (A) qRT-PCR analysis of Sl-IAA3 transcript levels in 3-week-old light-grown control and auxin-treated (20 μM IAA for 2 h) seedlings in presence or absence of 1 μl l−11-MCP applied 16 h prior to auxin treatment. Relative expression level on the y-axis refers to the fold difference in SI-IAA3 transcript levels relative to the non-treated plantlets. (B) Auxin responsiveness of the Sl-IAA3 promoter. Tobacco protoplasts were transformed by PIAA3::GFP and incubated in the presence or absence of 2,4-D (50 μM). Transformation was performed in triplicate and, in each experiment, GFP fluorescence was measured by flow cytometry 16 h after transfection. Values are expressed in arbitrary units (a.u.) ±standard error. (C–F) Tissue-specific expression of Sl-IAA3 assessed in transgenic tomato expressing GUS reporter gene driven by the Sl-IAA3 promoter (PIAA3::GUS). The expression pattern was analysed in 3-week-old seedlings (C), leaves (D), roots (E), and MG fruit (F). (G–J) These images correspond to the same tissues treated for 2 h with 20 μM IAA. (K–N) These images correspond to the same tissues expressing the DR5 auxin-responsive promoter fused to the GUS reporter gene (DR5::GUS) and those in (O–R) to DR5::GUS treated with 20 μM IAA. The data are representative of at least three independent experiments with n > 20 seedlings examined per experiment.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2657550&req=5

fig3: Auxin responsiveness of the Sl-IAA3 gene. (A) qRT-PCR analysis of Sl-IAA3 transcript levels in 3-week-old light-grown control and auxin-treated (20 μM IAA for 2 h) seedlings in presence or absence of 1 μl l−11-MCP applied 16 h prior to auxin treatment. Relative expression level on the y-axis refers to the fold difference in SI-IAA3 transcript levels relative to the non-treated plantlets. (B) Auxin responsiveness of the Sl-IAA3 promoter. Tobacco protoplasts were transformed by PIAA3::GFP and incubated in the presence or absence of 2,4-D (50 μM). Transformation was performed in triplicate and, in each experiment, GFP fluorescence was measured by flow cytometry 16 h after transfection. Values are expressed in arbitrary units (a.u.) ±standard error. (C–F) Tissue-specific expression of Sl-IAA3 assessed in transgenic tomato expressing GUS reporter gene driven by the Sl-IAA3 promoter (PIAA3::GUS). The expression pattern was analysed in 3-week-old seedlings (C), leaves (D), roots (E), and MG fruit (F). (G–J) These images correspond to the same tissues treated for 2 h with 20 μM IAA. (K–N) These images correspond to the same tissues expressing the DR5 auxin-responsive promoter fused to the GUS reporter gene (DR5::GUS) and those in (O–R) to DR5::GUS treated with 20 μM IAA. The data are representative of at least three independent experiments with n > 20 seedlings examined per experiment.
Mentions: In dark-grown seedlings, qRT-PCR analysis revealed that ethylene induction of Sl-IAA3 transcript accumulation mimicked both the dose-response and the time-course gradient of the well-characterized ethylene-responsive gene, E8 (see Fig. S1 in Supplementary data available at JXB online). Sl-IAA3 transcript levels also increased 4-fold in light-grown tomato seedlings after 2 h of auxin (20 μM IAA) treatment (Fig. 3A). In tobacco BY2 protoplasts transfection assays, Sl-IAA3 promoter (1668 bp)-driven GFP levels increased 4-fold after auxin treatment (50 μM 2,4-D) (Fig. 3B). As auxin is known to stimulate ethylene production (Abel et al., 1995), it was decided to determine whether this auxin-responsiveness resulted from an increase in ethylene production. Light-grown tomato seedlings were treated overnight with 1-MCP (1μl l−1) and then incubated in presence or absence of auxin. Similarly to the observation in fruit, 1-MCP almost completely abolished SI-IAA3 transcripts in untreated tomato seedlings (Fig. 3A). In the presence of both 1-MCP and auxin, however, Sl-IAA3 transcript levels were only partially reduced (Fig. 3A), indicating that in light-grown tomato seedlings SI-IAA3 is both auxin and ethylene-inducible and that the auxin-responsiveness is partially mediated by ethylene.

Bottom Line: Sl-IAA3 expression is auxin and ethylene dependent, is regulated on a tight tissue-specific basis, and is associated with tissues undergoing differential growth such as in epinastic petioles and apical hook.Antisense down-regulation of Sl-IAA3 results in auxin and ethylene-related phenotypes, including altered apical dominance, lower auxin sensitivity, exaggerated apical hook curvature in the dark and reduced petiole epinasty in the light.The results provide novel insights into the roles of Aux/IAAs and position the Sl-IAA3 protein at the crossroads of auxin and ethylene signalling in tomato.

View Article: PubMed Central - PubMed

Affiliation: Université de Toulouse, INP-ENSA Toulouse, Génomique et Biotechnologie des Fruits, Avenue de l'Agrobiopole BP 32607, Castanet-Tolosan F-31326, France.

ABSTRACT
Whereas the interplay of multiple hormones is essential for most plant developmental processes, the key integrating molecular players remain largely undiscovered or uncharacterized. It is shown here that a member of the tomato auxin/indole-3-acetic acid (Aux/IAA) gene family, Sl-IAA3, intersects the auxin and ethylene signal transduction pathways. Aux/IAA genes encode short-lived transcriptional regulators central to the control of auxin responses. Their functions have been defined primarily by dominant, gain-of-function mutant alleles in Arabidopsis. The Sl-IAA3 gene encodes a nuclear-targeted protein that can repress transcription from auxin-responsive promoters. Sl-IAA3 expression is auxin and ethylene dependent, is regulated on a tight tissue-specific basis, and is associated with tissues undergoing differential growth such as in epinastic petioles and apical hook. Antisense down-regulation of Sl-IAA3 results in auxin and ethylene-related phenotypes, including altered apical dominance, lower auxin sensitivity, exaggerated apical hook curvature in the dark and reduced petiole epinasty in the light. The results provide novel insights into the roles of Aux/IAAs and position the Sl-IAA3 protein at the crossroads of auxin and ethylene signalling in tomato.

Show MeSH
Related in: MedlinePlus