Transcriptome analysis reveals regulatory effects of exogenous gibberellin on locule number in tomato
2020
The size and shape of tomato (Solanum lycopersicum L.) fruit are determined by locule number. Gibberellin (GA) can increase locule number in tomato, but the underlying molecular mechanism is unclear. Therefore, in this study, multi-locule ‘MLK1’ tomato seedlings with two to three true leaves (pre-flower bud differentiation) were sprayed with GA₁, GA₃, GA₄, GA₇, PAC (paclobutrazol; an inhibitor of GA biosynthesis) and H₂O, as a control. We found that GA₄ resulted in was the most significant increase in tomato locule number among all bioactive GAs, while PAC decreased the locule number. We analyzed the change in locule number by RNA-seq, quantitative real-time PCR and ultra-performance liquid chromatography–tandem mass spectrometry. The categories ‘Phenylpropanoid biosynthesis’, ‘Plant hormone signal transduction’, and ‘Diterpenoid biosynthesis’ were considerably activated after spraying with GA₄. Additionally, indole-3-acetic acid (IAA) content significantly increased and trans-Zeatin-riboside (tZ) content significantly reduced after exogenous GA₄ application. We conclude that exogenous GA₄ application changed the dynamic balance of hormones in the tomato shoot apex. Furthermore, 53 differentially expressed transcription factors were identified in tomato upon exogenous GA₄ treatment during floral bud differentiation, including, YABBYs, TCP, NAC, and ARR (some directly regulate lateral organ development). Our results provide novel insights into how exogenous GA₄ affects plant hormone homeostasis in the tomato shoot apex and the underlying mechanism of locule number regulation by GA₄ in tomato.
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