Transcriptome analysis reveals regulatory effects of exogenous gibberellin on locule number in tomato

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 GA 1 , GA 3 , GA 4 , GA 7 , PAC (paclobutrazol; an inhibitor of GA biosynthesis) and H 2 O, as a control. We found that GA 4 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 GA 4 . Additionally, indole-3-acetic acid (IAA) content significantly increased and trans-Zeatin-riboside (tZ) content significantly reduced after exogenous GA 4 application. We conclude that exogenous GA 4 application changed the dynamic balance of hormones in the tomato shoot apex. Furthermore, 53 differentially expressed transcription factors were identified in tomato upon exogenous GA 4 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 GA 4 affects plant hormone homeostasis in the tomato shoot apex and the underlying mechanism of locule number regulation by GA 4 in tomato.