RT Journal Article
SR Electronic
T1 Distinct ROPGEFs successively drive polarization and outgrowth of root hairs
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 534545
DO 10.1101/534545
A1 Philipp Denninger
A1 Anna Reichelt
A1 Vanessa A. F. Schmidt
A1 Dietmar G. Mehlhorn
A1 Lisa Y. Asseck
A1 Claire E. Stanley
A1 Nana F. Keinath
A1 Jan-Felix Evers
A1 Christopher Grefen
A1 Guido Grossmann
YR 2019
UL http://biorxiv.org/content/early/2019/01/29/534545.abstract
AB Root hairs are tubular protrusions of the root epidermis that significantly enlarge the exploitable soil volume in the rhizosphere. Trichoblasts, the cell type responsible for root hair formation, switch from cell elongation to tip growth through polarization of the growth machinery to a pre-defined root hair initiation domain (RHID) at the plasma membrane. The emergence of this polar domain resembles the establishment of cell polarity in other eukaryotic systems [1–3]. Rho-type GTPases of plants (ROPs) are among the first molecular determinants of the RHID [4, 5] and later play a central role in polar growth [6]. Numerous studies have elucidated mechanisms that position the RHID in the cell [7–9] or regulate ROP activity [10–18]. The molecular players that target ROPs to the RHID and initiate outgrowth, however, have not been identified. We dissected the timing of the growth machinery assembly in polarizing hair cells and found that positioning of molecular players and outgrowth are temporally separate processes that are each controlled by specific ROP guanine nucleotide exchange factor (GEFs). A functional analysis of trichoblast-specific GEFs revealed GEF3 to be required for normal ROP polarization and thus efficient root hair emergence, while GEF4 predominantly regulates subsequent tip growth. Ectopic expression of GEF3 induced the formation of spatially confined, ROP-recruiting domains in other cell types, demonstrating the role of GEF3 to serve as a membrane landmark during cell polarization. Our findings suggest that morphogenetic programs in plants employ distinct regulatory modules for the alignment and activation of the cellular growth machinery.