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

Abstract

The <i>Arabidopsis thaliana</i> NAC transcription factor JUNGBRUNNEN1 (AtJUB1) regulates growth by directly repressing <i>GA3ox1</i> and <i>DWF4</i>, 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 <i>PIF4</i>, a bHLH transcription factor that positively controls cell elongation, while it stimulates the expression of <i>DELLA</i> genes, which are important repressors of growth. Here, we extend our previous findings by demonstrating that <i>AtJUB1</i> induces similar GA and BR deficiency phenotypes and changes in gene expression when overexpressed in tomato (<i>Solanum lycopersicum</i>). Importantly, and in accordance with the growth phenotypes observed, AtJUB1 inhibits the expression of growth-supporting genes, namely the tomato orthologs of <i>GA3ox1</i>, <i>DWF4</i> and <i>PIF4</i>, but activates the expression of <i>DELLA</i> orthologs, by directly binding to their promoters. Overexpression of <i>AtJUB1</i> 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 <i>PIF4</i> genes but acts as a direct activator of <i>DELLA</i> genes in both, <i>Arabidopsis</i> and tomato, strongly supports the model that the molecular constituents of the JUNGBRUNNEN1 growth control module are considerably conserved across species.