S mainly functions as a repressor regulating fruit growth and seed development (PRJCA033966)

In most fruit-bearing plants, the growth and ripening of the fruit are highly coordinated with the development of the seeds it contains. In tomato (Solanum lycopersicum), an important vegetable crop cultivated globally, fruit growth is regulated by a number of transcription factors. The WUSCHEL-RELATED HOMEOBOX (WOX) transcription factor COMPOUND INFLORESCENCE (S)/SlWOX9 is a significant regulator of inflorescence branching and embryogenesis. In this study, we show that S activity is required for fruit and seed development. Ectopic S expression led to a decrease in seed weight and markedly suppressed the endoreduplication-associated fruit growth regardless of genetic backgrounds. In contrast, the s-classic allele promoted fruit growth in S. pimpinellifolium, but its effect was offset by excessive fruit overload and vegetative reversion of flowers in large-fruited cultivars. Through transcriptome profiling and DNA affinity purification sequencing (DAP-seq), we discovered that S targeted a set of genes involved in seed development. Additionally, we demonstrate that S mainly functions as a repressor that directly regulates the transcription of the Mei2-like gene SlTEL1 (Solanum lycopersicum TERMINAL EAR-LIKE 1) to control embryogenesis after fertilization. These findings uncover a new aspect of transcription regulation of fruit growth and seed development by WOX transcription factors in tomato.