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Functional characterization of tomato Sl-IAA3 and Sl-hls genes. Role ...

Functional characterization of tomato Sl-IAA3 and Sl-hls genes. Role ...

Chapitre II:

Chapitre II: Sl-IAA3, a Tomato Aux/IAA at the Crossroads of Auxin and Ethylene Signalling phenotype of the AS-IAA3 plants requires active ethylene signalling and that transgenic lines are more responsive to ethylene. B D % % 80 60 40 20 0 50 40 30 20 10 0 1-MCP 0 1 2 3 4 5 6 7 Stages C2H4 0.1 µL L-1 C2H4 0.1 µL L-1 0 1 2 3 4 5 6 7 Stages C E % % 60 50 40 30 20 10 0 40 30 20 10 0 0 1 2 3 4 5 6 7 Stages C2H4 1 µL L-1 C2H4 1 µL L-1 0 1 2 3 4 5 6 7 Stages Figure 8. Increased Ethylene Sensitivity of AS-IAA3 Lines. A. Eight stages of hook formation have been defined (stage 0 to 7) in etiolated tomato seedlings treated with different concentrations of ethylene (0 to 1 µL L -1 ). B to E. Proportion of WT (black bars) and AS-IAA3 (grey bars) plants corresponding to the eight stages of hook formation upon treatment with (B) 1-MCP (1µL L -1 for 16 h), (C) air or (D and E) exogenous ethylene (0.1 and 1µL L -1 ). The Expression of Sl-IAA3 Is Tightly Regulated in Apical Hook and Epinastic Petiole upon Ethylene Treatment To further investigate the role of Sl-IAA3 in apical hook formation and epinastic response, we analyzed the expression pattern of this gene in the corresponding tissues of transgenic tomato lines expressing the GUS reporter gene driven by the Sl-IAA3 promoter (ProIAA3:GUS). In the absence of exogenous ethylene, there was no detectable GUS staining in the apical hook of dark-grown seedlings. By contrast, after 48 hours ethylene treatment (10 µL L -1 ), a strong band of GUS staining was observed on the inner surface of the apical hook. We also analysed the expression of the GUS reporter gene driven by the DR5 promoter in order to Air 65

Chapitre II: Sl-IAA3, a Tomato Aux/IAA at the Crossroads of Auxin and Ethylene Signalling determine whether ethylene treatment alters the expression pattern of this auxin sensor chimerical gene. Ethylene treatment did not affect the DR5:GUS staining pattern in the hook suggesting that the ethylene induction of Sl-IAA3 was not mediated through increased auxin levels in the treated tissue (Figure 9A). In epinastic petioles treated with ethylene, the expression of ProIAA3:GUS was restricted to the upper side of the leaf nods while no expression was detected in untreated non-epinastic petioles (Figure 9B). These data indicate that the expression of Sl-IAA3 is associated with tissues undergoing differential growth, both in etiolated seedlings and in epinastic petioles. Table 1. Altered Petiole Epinastic Response in AS-IAA3 Plants in Response to Ethylene. Petiole opening degree of the first and the second leaf node was measured before and after ethylene treatment in WT and AS-IAA3 plants. The data are means ± SE of at least 36 plants and are representative of three independent experiments WT AS-IAA3-1 AS-IAA3-2 Petiole opening degree Air C2H4 70.8° ± 2.8 100° ± 4.46 70.1° ± 3.5 87° ± 4.31 72.2° ± 1.8 75° ± 2.87 The Sl-IAA3 and Sl-HOOKLESS Genes Are Expressed on Opposite Sides of the Apical Hook In Arabidopsis, At-HOOKLESS1 (At-HLS1) is a key regulator of apical hook formation that has been proposed by Lehman et al. (1996) to integrate ethylene and auxin signalling during hook formation and maintenance in dark-grown seedlings. The Arabidopsis hls1 mutant showed no differential growth in the apical region of the hypocotyl even after ethylene treatment. We isolated a putative tomato ortholog of At-HLS1 and showed that it fully rescues the Arabidopsis hls1-1 mutant phenotype (see supplemental Figure 5 online). Accumulation of Sl-HLS transcripts is not altered in the AS-IAA3 plants (Figure11D) suggesting that the exaggerated hook formation in the transgenic lines does not involve an alteration in Sl-HLS expression. To further investigate 66

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