| Author |
Cory Rafsyanyani, Titah Rigel Anjalani, Anisa Esti Rahayu, Syariful Mubarok, Ani Widiastuti, Deden Derajat Matra, Hiroshi Ezura, Nurul Jadid
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| Abstract |
Rising temperatures associated with climate change threaten tomato productivity, yet the contribution of auxin signaling components to heat-stress adaptation remains incompletely understood. The <em>IAA9</em> gene, encoding an Aux/IAA transcriptional repressor, is well known for its role in auxin-regulated development, but its role in heat responses is still unclear. This study aims to elucidate the function of <em>IAA9</em> in modulating tomato responses under heat stress conditions. Researchers utilized tomato <em>iaa9-3</em> and <em>iaa9-5 </em>mutants and exposed them to prolonged elevated temperatures of 40 to 45 °C for 6 weeks to assess morphophysiological traits, and to 38 to 40 °C for 6 days to evaluate molecular responses through <em>SlDREBA4</em> gene expression analysis. Under prolonged heat stress, all genotypes exhibited reduced leaf area, leaf number, and total chlorophyll content, accompanied by increased plant height compared to plants grown under normal conditions. Specifically, wild-type Micro-Tom (WT-MT) showed the lowest values in leaf area (165.89 cm²), leaf number (23 leaves), and total chlorophyll content (115.7 µg g<sup>-1</sup>). In contrast, the <em>iaa9-3</em> and <em>iaa9-5</em> mutants recorded the highest plant heights at 11.98 and 12.13 cm, respectively, indicating a differential growth response under stress. Gene expression analysis revealed that <em>SlDREBA4</em> expression was upregulated in both <em>iaa9-3</em> and <em>iaa9-5 </em>mutants compared to normal temperature conditions, with increases of 0.45-fold and 1.78-fold, respectively. These results indicate that <em>IAA9</em> mutations confer enhanced thermotolerance in tomato, as reflected by altered morphology and increased heat-responsive gene expression. This study highlights <em>IAA9</em> as a potential genetic target for improving heat stress resilience in tomato breeding programs.
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