The long-term goal of this project is to understand the molecular networks through which hormones, environmental signals, and nutrients together control plant growth and development. As sessile organisms, plants have evolved complex and robust cellular signaling systems to regulate growth and metabolism according to internal status and environmental conditions. Dissecting these plant regulatory systems not only is important for crop resilience and food security but also can improve human health, as many signaling mechanisms are highly conserved in plants, humans, and human parasites. This research project aims to dissect the cellular signaling and regulatory networks that integrate hormonal, metabolic, and environmental signals. To gain a comprehensive understanding of the complex system, we integrate a broad range of research approaches including genetics, genomics, proteomics, structural biology, cell biology, and chemical proteomic approaches. We also use both muti-cellular and single-cellular model systems (Arabidopsis and Chlamydomonas) to gain insight into the conserved mechanisms such as cell cycle regulation and the evolution of inter-cellular signaling mechanisms underlying cell-cell communication, development, and morphogenesis. In the past two decades, we have elucidated molecular mechanisms by which the brassinosteroid (BR) hormone acts through the cell surface receptor kinase BRI1 and its downstream phosphorylation cascade to regulate gene expression and plant growth, cross-talks with other signaling pathways to regulate development and environmental responses, and intersects with sugar-signaling pathways to optimize growth and acclimation. We have also discovered signaling mechanisms that regulate cell division, elongation, differentiation, and innate immunity. Furthermore, we have recently generated proteomic maps of the nutrient/sugar-sensing O-glycosylation (O-GlcNAc and O-fucose) pathways and discovered their convergence with the BR-regulated phosphorylation pathway. Our research elucidates a signal- processing network that controls plant growth according to nutrient/sugar availability, hormonal instructions, and environmental cues, and increases our molecular insight into signaling mechanisms involving protein-protein interactions and protein modifications by phosphorylation and glycosylation. We focus on proteins that are conserved in humans or human parasites, and thus our research also informs medical research. Our research will benefit human well-being by improving food security, environmental sustainability, and drug development/discovery.