SPIKE1, a plant rho guanine nucleotide exchange factor, integrates endomembrane transport and cytoskeletal functions
Abstract
Understanding the mechanisms of cell growth control is fundamentally important for plant biology and biotechnology. For example, cell shape changes in guard cells control efficient water use, cell-cell interactions maintain the integrity of the epidermis during growth, and root hair deformation is an important early event during nodulation and efficient nitrogen use. All of these cellular dynamics require integrated control of cell wall properties, vesicle trafficking, and the actin cytoskeleton. Previous work in Arabidopsis and other species have demonstrated the importance of the actin related protein (ARP) 2/3 actin filament nucleation pathway in each of the above processes, and has provided an experimentally tractable system to discover conserved growth control mechanisms. My Ph. D. thesis research focuses on understanding the upstream regulation of the ARP2/3 complex and actin nucleation. ARP2/3 by itself is inactive. How do members of the SCAR gene family proteins positively regulate ARP2/3? We find that all SCARs potently activate the actin filament nucleation of ARP2/3, and the relative importance of different SCAR genes is related to the biochemical efficiency of ARP2/3 activation and the steady state levels of SCAR mRNAs within a particular cell type. The evolutionary and developmental issues of unequal gene functions will be discussed. I also describe cellular data about how activating signals are transmitted to SCAR proteins through Rho family small GTPases, termed Rho of Plants (ROP). We found that SPIKE1, an upstream positive regulator of ROP, assembles a signaling scaffold within specialized domains of the endoplasmic reticulum. These unexpected results define new relationships between small GTPase activation, vesicle trafficking, and the actin cytoskeleton.
Degree
Ph.D.
Advisors
Szymanski, Purdue University.
Subject Area
Molecular biology|Plant biology|Genetics|Cellular biology
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