NAC Transcription Factor JUNGBRUNNEN1 Exerts Conserved Control Over Gibberellin and Brassinosteroid Metabolism and Signaling Genes in Tomato.

The NAC transcription factor JUNGBRUNNEN1 (AtJUB1) regulates growth by directly repressing and , two key genes involved in gibberellin (GA) and brassinosteroid (BR) biosynthesis, respectively, leading to GA and BR deficiency phenotypes. AtJUB1 also reduces the expression of , a bHLH transcription factor that positively controls cell elongation, while it stimulates the expression of genes, which are important repressors of growth. Here, we extend our previous findings by demonstrating that induces similar GA and BR deficiency phenotypes and changes in gene expression when overexpressed in tomato (). Importantly, and in accordance with the growth phenotypes observed, AtJUB1 inhibits the expression of growth-supporting genes, namely the tomato orthologs of , and , but activates the expression of orthologs, by directly binding to their promoters. Overexpression of in tomato delays fruit ripening, which is accompanied by reduced expression of several ripening-related genes, and leads to an increase in the levels of various amino acids (mostly proline, β-alanine, and phenylalanine), γ-aminobutyric acid (GABA), and major organic acids including glutamic acid and aspartic acid. The fact that AtJUB1 exerts an inhibitory effect on the GA/BR biosynthesis and genes but acts as a direct activator of genes in both, and tomato, strongly supports the model that the molecular constituents of the JUNGBRUNNEN1 growth control module are considerably conserved across species.