The survival of multicellular organisms depends on cell communication that coordinates the metabolism, growth, and differentiation of cells in diverse tissues and organs. A primary mechanism by which cells communicate with each other is through hormones. Among the many types of hormones, steroids are particularly interesting because they are used as signaling molecules by both plants and animals, which diverged more than 1 billion years ago, to control a wide range of developmental processes. In animals, steroid hormones initiate their signaling processes by diffusing freely into
cells where they interact with specific intracellular receptors, which can then move into the nucleus and directly act as a gene regulatory switch to turn genes “on” or “off”, thus altering protein synthesis and leading to a defined set of cellular responses. In contrast, plant steroids (known as brassinosteroids) are perceived by transmembrane receptor kinases at the cell surface, leading to the activation of a phosphorylation-mediated signaling cascade that changes the expression of many steroid-responsive genes.
The research of my laboratory is mainly focused on studying the molecular mechanism of the plant steroid signaling process using Arabidopsis as the model organism. Through genetic and yeast two-hybrid screens, we have identified several critical components of the plant steroid signaling pathway, which include two similar yet distinct leucine-rich-repeat receptor-like kinases, a GSK3-like kinase, and two highly-homologous nuclear proteins. Currently, we are taking a combinatory approach of biochemistry, cell biology, and genetics to investigate how the two transmembrane receptor kinases transmit the steroid signal across the cell membrane, how the membrane-initiated steroid signal is transduced within the plant cell, and how the two nuclear proteins interact with other transcriptional factors to regulate gene expression inside the nucleus.