The brassinosteroid signaling network — a paradigm of signal integration

• The BZR–ARF–PIF/DELLA module integrates major hormonal and environmental signals.
• BZR–ARF–PIF/DELLA module is coupled with the PRE-IBH1–HBI1 tripartite HLH/bHLH module.
• Biotic and abiotic stresses antagonize growth-promoting pathways at multiple levels.
• BIN2/GSK3 mediates crosstalks between BR and other receptor kinase pathways.
• The TDR receptor kinase phosphorylates BIN2 to regulate xylem and lateral root development.

Many hormonal and environmental signals regulate common cellular and developmental processes in plants. While the molecular pathways that transduce these signals have each been studied in detail, how these pathways are wired into regulatory networks to provide the coordinated responses has remained an outstanding question. Recent studies of the brassinosteroid signaling network have revealed extensive signal integration through direct interactions between components of different signaling pathways. In particular, a circuit of interacting transcription regulators integrates many signaling pathways to enable coordinated and coherent regulation of seedling morphogenesis by hormonal and environmental signals. The recent studies support an emerging theme that complex networks of highly integrated signaling pathways underlie the high levels of developmental plasticity and environmental adaptability of plants.