Title:The unexpected cellular deployment of signaling and cytoskeletal complexes during leaf epidermal morphogenesis

Presenter: Prof. Dan Szymanski

University: Department of Agronomy, Purdue University

Time: 9:30-10:30, 9 May, 2011

Venue: A203, Institute of Microbiology, Chinese Academy of Sciences

Abstract:

The leaf epidermis is a biomechanical shell, the growth of which can affect the behavior of underlying cell layers and the overall architectural properties of the leaf. Understanding the genetic and molecular basis of its morphogenesis is an important problem in basic research and applied plant science. Arabidopsis pavement cell and trichome morphology mutants continue to identify new genes and biochemical pathways that affect the growth process; however, it is unclear how these complicated networks of proteins interact with the endomembrane and cytoskeletal systems to initiate and maintain polarized growth. The ROP small GTPase exchange factor SPIKE1 and “distorted” actin based growth control system is a perfect example. Genetic and biochemical analyses provide a logic model for information flow from the formation of a ROP activation scaffold through a series of heteromeric protein complexes (WAVE/SCAR and ARP2/3) that generate an actin filament nucleation response. The cellular deployment of the pathway is unknown. It is commonly believed that during polarized growth ROP activation must be restricted to specific cortical domains. Contrary to this notion, our most recent results suggest that abundant subdomains of the ER termed ER exit sites serve as a distributed network of SPK1-ROP activation sites. This seminar will provide an update of our live cell imaging, genetic, and biochemical analyses that indicate that SPK1 signals diverge from ERES to control distinct trafficking and cytoskeletal activities. I will discuss how signal generation and cytoskeletal responses are compartmentalized in the cell and how this unexpected cellular deployment might regulate the morphogenesis at the spatial scale of a cell.