Actin dynamics in Phytophthora infestans; rapidly reorganizing cables and immobile, long-lived plaques
Meijer, H.J.G. ; Hua, C. ; Kots, K. ; Ketelaar, T. ; Govers, F. - \ 2014
Cellular Microbiology 16 (2014)6. - ISSN 1462-5814 - p. 948 - 961.
oomycete achlya-bisexualis - f-actin - hyphal growth - tip growth - quantitative-analysis - aspergillus-nidulans - arabidopsis-thaliana - neurospora-crassa - saprolegnia-ferax - patch movement
The actin cytoskeleton is a dynamic but well organized intracellular framework that is essential for proper functioning of eukaryotic cells. Here, we use the actin binding peptide Lifeact to investigate the in vivo actin cytoskeleton dynamics in the oomycete plant pathogen Phytophthora infestans. Lifeact-eGFP labelled thick and thin actin bundles and actin filament plaques allowing visualization of actin dynamics. All actin structures in the hyphae were cortically localized. In growing hyphae actin filament cables were axially oriented in the sub-apical region whereas in the extreme apex in growing hyphae, waves of fine F-actin polymerization were observed. Upon growth termination, actin filament plaques appeared in the hyphal tip. The distance between a hyphal tip and the first actin filament plaque correlated strongly with hyphal growth velocity. The actin filament plaques were nearly immobile with average lifetimes exceeding one hour, relatively long when compared to the lifetime of actin patches known in other eukaryotes. Plaque assembly required ~30 seconds while disassembly was accomplished in ~10 sec. Remarkably, plaque disassembly was not accompanied with internalization and the formation of endocytic vesicles. These findings suggest that the functions of actin plaques in oomycetes differ from those of actin patches present in other organisms.
A Phytophthora sojae G protein alpha subunit is involved in chemotaxis to soybean isoflavones
Hua, C. ; Wang, Y. ; Zheng, X. ; Dou, D. ; Zhang, Z. ; Govers, F. - \ 2008
Eukaryotic Cell 7 (2008)12. - ISSN 1535-9778 - p. 2133 - 2140.
transcription factor - zoospore encystment - hyphal growth - saccharomyces-cerevisiae - signal-transduction - cyst germination - botrytis-cinerea - beta-subunit - infestans - oomycete
For the soybean pathogen Phytophthora sojae, chemotaxis of zoospores to isoflavones is believed to be critical for recognition of the host and for initiating infection. However, the molecular mechanisms underlying this chemotaxis are largely unknown. To investigate the role of G-protein and calcium signaling in chemotaxis, we analyzed the expression of several genes known to be involved in these pathways and selected one that was specifically expressed in sporangia and zoospores but not in mycelium. This gene, named PsGPA1, is a single-copy gene in P. sojae and encodes a G-protein subunit that shares 96% identity in amino acid sequence with that of Phytophthora infestans. To elucidate the function, expression of PsGPA1 was silenced by introducing antisense constructs into P. sojae. PsGPA1 silencing did not disturb hyphal growth or sporulation but severely affected zoospore behavior, including chemotaxis to the soybean isoflavone daidzein. Zoospore encystment and cyst germination were also altered, resulting in the inability of the PsGPA1-silenced mutants to infect soybean. In addition, the expressions of a calmodulin gene, PsCAM1, and two calcium- and calmodulin-dependent protein kinase genes, PsCMK3 and PsCMK4, were increased in the mutant zoospores, suggesting that PsGPA1 negatively regulates the calcium signaling pathways that are likely involved in zoospore chemotaxis