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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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Altered vegetative growth phenotypes in antisense Sl-IAA3 plants. (A) Down-regulation of Sl-IAA3 in transgenic tomato plants. The level of Sl-IAA3 transcripts in antisense lines (1 and 2) was assessed by qRT-PCR. Relative expression level refers to the fold difference in Sl-IAA3 transcript levels relative to the wild type (WT). (B) Reduced apical dominance in 7-week-old AS-IAA3 plants compared with WT. (C) The number of lateral shoots branching from the first leaf node in WT and AS-IAA3 plants. The data are the mean ±standard error of 30 plants and are representative of three independent experiments. (D) Auxin dose-response in hypocotyl segments. Hypocotyl fragments (8 mm long) from 3-week-old light-grown seedlings were incubated for 2 h in the presence of the indicated concentration of NAA. Elongation is given as percentage increase in final length over the initial length. The results are representative of data obtained with two independent AS-IAA3 lines and with two replicates for each line. Standard errors are indicated (n ≥25). (This figure is available in colour at JXB online.)
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fig4: Altered vegetative growth phenotypes in antisense Sl-IAA3 plants. (A) Down-regulation of Sl-IAA3 in transgenic tomato plants. The level of Sl-IAA3 transcripts in antisense lines (1 and 2) was assessed by qRT-PCR. Relative expression level refers to the fold difference in Sl-IAA3 transcript levels relative to the wild type (WT). (B) Reduced apical dominance in 7-week-old AS-IAA3 plants compared with WT. (C) The number of lateral shoots branching from the first leaf node in WT and AS-IAA3 plants. The data are the mean ±standard error of 30 plants and are representative of three independent experiments. (D) Auxin dose-response in hypocotyl segments. Hypocotyl fragments (8 mm long) from 3-week-old light-grown seedlings were incubated for 2 h in the presence of the indicated concentration of NAA. Elongation is given as percentage increase in final length over the initial length. The results are representative of data obtained with two independent AS-IAA3 lines and with two replicates for each line. Standard errors are indicated (n ≥25). (This figure is available in colour at JXB online.)

Mentions: Several independent homozygous Sl-IAA3-suppressed antisense lines (AS-IAA3) were generated and two representative lines (1 and 2) with 3.5-fold and 10-fold reductions, respectively, in Sl-IAA3 transcript levels were selected for further study (Fig. 4A). Down-regulation of Sl-IAA3 resulted in a variety of vegetative growth phenotypes (Figs 4, 5). In determinate wild-type tomato plants, lateral shoots develop only after floral transition, and their growth is initiated in an apical–basal sequence along the primary shoot axis. In the AS-IAA3 plants, by contrast, axillary shoot development began in the lowest leaf node (Fig. 4B) and the number of lateral shoots was greater in the transgenic lines (Fig. 4C). This loss of apical dominance suggests a reduced response to endogenous auxin in the transgenic lines. Similarly, auxin-induced hypocotyl elongation was reduced in AS-IAA3 hypocotyls compared with the wild type (Fig. 4D), further indicating a reduction in auxin responsiveness in the transgenic lines. To investigate this apparent reduction in auxin responsiveness, the effects of the auxin transport inhibitor N-1-napthylphthalamic acid (NPA) on the growth of wild-type and AS-IAA3 seedlings were examined. Wild-type seedlings grown in the presence of 1 μM NPA showed a marked reduction in primary root elongation and a complete suppression of lateral root formation (Fig. 5A, B). By contrast, NPA only weakly affected primary and lateral root growth in the AS-IAA3 plants (Fig. 5A, B). Also, leaf emergence was strongly inhibited in NPA-treated wild-type seedlings, but not in the AS-IAA3 plants (arrow in Fig. 5A). The AS-IAA3 lines also had a higher frequency of ectopic cotyledons than the wild type (Fig. 5C, D). The frequency of polycotyledons was 25% and 20% in AS-AA3-1 and AS-IAA3-2 lines, respectively, compared with only 5% in the wild type (Fig. 5D).


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)

Altered vegetative growth phenotypes in antisense Sl-IAA3 plants. (A) Down-regulation of Sl-IAA3 in transgenic tomato plants. The level of Sl-IAA3 transcripts in antisense lines (1 and 2) was assessed by qRT-PCR. Relative expression level refers to the fold difference in Sl-IAA3 transcript levels relative to the wild type (WT). (B) Reduced apical dominance in 7-week-old AS-IAA3 plants compared with WT. (C) The number of lateral shoots branching from the first leaf node in WT and AS-IAA3 plants. The data are the mean ±standard error of 30 plants and are representative of three independent experiments. (D) Auxin dose-response in hypocotyl segments. Hypocotyl fragments (8 mm long) from 3-week-old light-grown seedlings were incubated for 2 h in the presence of the indicated concentration of NAA. Elongation is given as percentage increase in final length over the initial length. The results are representative of data obtained with two independent AS-IAA3 lines and with two replicates for each line. Standard errors are indicated (n ≥25). (This figure is available in colour at JXB online.)
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig4: Altered vegetative growth phenotypes in antisense Sl-IAA3 plants. (A) Down-regulation of Sl-IAA3 in transgenic tomato plants. The level of Sl-IAA3 transcripts in antisense lines (1 and 2) was assessed by qRT-PCR. Relative expression level refers to the fold difference in Sl-IAA3 transcript levels relative to the wild type (WT). (B) Reduced apical dominance in 7-week-old AS-IAA3 plants compared with WT. (C) The number of lateral shoots branching from the first leaf node in WT and AS-IAA3 plants. The data are the mean ±standard error of 30 plants and are representative of three independent experiments. (D) Auxin dose-response in hypocotyl segments. Hypocotyl fragments (8 mm long) from 3-week-old light-grown seedlings were incubated for 2 h in the presence of the indicated concentration of NAA. Elongation is given as percentage increase in final length over the initial length. The results are representative of data obtained with two independent AS-IAA3 lines and with two replicates for each line. Standard errors are indicated (n ≥25). (This figure is available in colour at JXB online.)
Mentions: Several independent homozygous Sl-IAA3-suppressed antisense lines (AS-IAA3) were generated and two representative lines (1 and 2) with 3.5-fold and 10-fold reductions, respectively, in Sl-IAA3 transcript levels were selected for further study (Fig. 4A). Down-regulation of Sl-IAA3 resulted in a variety of vegetative growth phenotypes (Figs 4, 5). In determinate wild-type tomato plants, lateral shoots develop only after floral transition, and their growth is initiated in an apical–basal sequence along the primary shoot axis. In the AS-IAA3 plants, by contrast, axillary shoot development began in the lowest leaf node (Fig. 4B) and the number of lateral shoots was greater in the transgenic lines (Fig. 4C). This loss of apical dominance suggests a reduced response to endogenous auxin in the transgenic lines. Similarly, auxin-induced hypocotyl elongation was reduced in AS-IAA3 hypocotyls compared with the wild type (Fig. 4D), further indicating a reduction in auxin responsiveness in the transgenic lines. To investigate this apparent reduction in auxin responsiveness, the effects of the auxin transport inhibitor N-1-napthylphthalamic acid (NPA) on the growth of wild-type and AS-IAA3 seedlings were examined. Wild-type seedlings grown in the presence of 1 μM NPA showed a marked reduction in primary root elongation and a complete suppression of lateral root formation (Fig. 5A, B). By contrast, NPA only weakly affected primary and lateral root growth in the AS-IAA3 plants (Fig. 5A, B). Also, leaf emergence was strongly inhibited in NPA-treated wild-type seedlings, but not in the AS-IAA3 plants (arrow in Fig. 5A). The AS-IAA3 lines also had a higher frequency of ectopic cotyledons than the wild type (Fig. 5C, D). The frequency of polycotyledons was 25% and 20% in AS-AA3-1 and AS-IAA3-2 lines, respectively, compared with only 5% in the wild type (Fig. 5D).

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