SlMADS50, A Type I MADS-box transcription factor, regulates tomato plant architecture via hormonal pathways

The MADS-box gene regulates plant growth and development. We cloned the type I MADS-box gene SlMADS50, which is relatively highly expressed in tomato roots, leaves and lateral buds, suggesting that it may be involved in the growth regulation of tomato vegetative organs. Subcellular localization results showed that the SlMADS50 protein was located in the nucleus. In this study, the classical tomato cultivar Ailsa Craig (AC⁺⁺) was used as background material to silence SlMADS50 gene by RNA interference. Compared with the wild type, SlMADS50-silenced lines exhibited lower apical dominance and reduced plant height. The length, width, perimeter and area of leaves were smaller than wild type plants. The total length, total surface area, total projected area, volume, forks and tips of roots were significantly reduced. Anatomical studies showed that the cells in the longitudinal section of the SlMADS50-silenced stem were smaller, but their average number was significantly increased. At the hormonal levels, the contents of IAA (indole-3-acetic acid), GA3(gibberellin A3), TZR (transzein riboside) and CS (castasterone) in SlMADS50-silenced lines were decreased. At the molecular level, auxin response gene SlIAA3 and gibberellin synthesis genes SlGA3ox1 were significantly down-regulated in SlMADS50-silenced lines, while the negative regulator of GA signaling, SlDELLA, were significantly up-regulated in the silenced lines. Based on the yeast two-hybrid assay showing that SlMADS50 interacts individually with RBCS3 and PUB22-like, we further speculate that SlMADS50 may regulate tomato plant architecture through photosynthetic and hormonal pathways. This study elucidated the biological function of SlMADS50 and its regulatory network in controlling tomato plant architecture. The findings not only advanced the understanding of type I MADS-box genes in tomato but also provide a reliable theoretical foundation for further research on plant architecture regulation in tomato.