INDETERMINATE DOMAIN-DELLA protein interactions orchestrate gibberellin-mediated cell elongation in wheat and barley
DELLA proteins, members of the GRAS-domain family of transcriptional regulators, are critical for plant growth and development. They modulate transcription indirectly via interactions with hundreds of transcription factors. The phytohormone gibberellin (GA) triggers DELLA degradation, providing a mechanism by which plants can integrate developmental and environmental signals to regulate gene expression and optimize growth responses. In agriculture, DELLA mutations have been instrumental in improving crop performance. Most modern wheat (Triticum aestivum L.) varieties carry Rht-B1b or Rht-D1b alleles that encode DELLA proteins resistant to GA-mediated degradation, resulting in constitutive partial suppression of stem growth, a semi-dwarf stature and lodging resistance. However, these alleles also reduce nitrogen use efficiency and early vigour, limiting their utility in some environments. Understanding how DELLA proteins regulate growth and development is, therefore, critical for refining breeding strategies. In this study, we identified the orthologous C2H2 zinc-finger transcription factors INDETERMINATE DOMAIN 5 (IDD5) in wheat and SEMI-DWARF 3 (SDW3) in barley (Hordeum vulgare) as positive regulators of stem and leaf expansion. Both IDD5 and SDW3 physically interact with, and act downstream of, DELLA proteins as key components of GA-mediated growth responses. Altered expression levels of GA biosynthesis genes suggest that IDD5 helps maintain GA homeostasis in addition to growth regulation. Loss-of-function mutations in IDD5 and SDW3 confer a GA-insensitive semi-dwarf phenotype comparable to that of the Rht-D1b Green Revolution allele, highlighting their potential as novel dwarfing alleles for cereal improvement. Significance statementOur study identifies homologous wheat and barley transcription factors (IDD5 and SDW3) that interact with DELLA proteins to regulate plant height. Unlike conventional Green Revolution DELLA mutations, which can reduce height but also have drawbacks such as lower nitrogen-use efficiency, these IDD genes may provide more targeted approaches to manage plant growth. By showing how IDD proteins promote stem and leaf expansion and by revealing their potential as alternative dwarfing alleles, our research opens new avenues both for fundamental research into plant growth pathways and for applications in cereal breeding. Ultimately, it could help produce crops with improved lodging resistance and fewer negative side effects than current dwarfing alleles.