Comparative genomics of the HOG-signalling system in fungi

Abstract

Signal transduction pathways play crucial roles in cellular adaptation to environmental changes. In this study, we employed comparative genomics to analyse the high osmolarity glycerol pathway in fungi. This system contains several signalling modules that are used throughout eukaryotic evolution, such as a mitogen-activated protein kinase and a phosphorelay module. Here we describe the identification of pathway components in 20 fungal species. Although certain proteins proved difficult to identify due to low sequence conservation, a main limitation was incomplete, low coverage genomic sequences and fragmentary genome annotation. Still, the pathway was readily reconstructed in each species, and its architecture could be compared. The most striking difference concerned the Sho1 branch, which frequently does not appear to activate the Hog1 MAPK module, although its components are conserved in all but one species. In addition, two species lacked apparent orthologues for the Sln1 osmosensing histidine kinase. All information gathered has been compiled in an MS Excel sheet, which also contains interactive visualisation tools. In addition to primary sequence analysis, we employed analysis of protein size conservation. Protein size appears to be conserved largely independently from primary sequence and thus provides an additional tool for functional analysis and orthologue identification.

Pulsing cells: How fast is too fast?

“…They found that the Sln1 branch dominated the activation dynamics of the HOG pathway and allowed cells to integrate fast fluctuating inputs from the environment. This observation is interesting when contrasted with the fact that while yeast has two branches that feed into the osmoadaptation pathway, it is the faster Sln1 branch, and not the Sho1 branch, that is conserved in fungi, indicating the importance of a fast response to osmolar changes in the environment (Furukawa et al, 2005;Krantz et al, 2006). Their results also suggest that the HOG pathway bandwidth is likely to be limited by the deactivation rates of components at or downstream of Pbs2, thereby highlighting the role of pathway phosphatases as an avenue for future investigation.…”

Transient responses during hyperosmotic shock in the filamentous fungus Neurospora crassa

“…The transduction pathway that controls turgor regulation is the osmotic MAP kinase pathway. The pathway has been characterized most completely in yeast (O'Rourke et al, 2002), and is found in numerous fungal species on the basis of comparative genomics (Krantz et al, 2006). In N. crassa, a histidine kinase sensor OS-1 (Alex et al, 1996;Miller et al, 2002) and an associated response regulator RRG-1 (Jones et al, 2007) function upstream of the MAPKKK OS-4 and MAPKK OS-5 (Fujimura et al, 2003), and MAPK OS-2 (Zhang et al, 2002), to elicit both glycerol accumulation (Noguchi et al, 2007) and ion accumulation (Lew et al, 2006) during turgor recovery after hyperosmotic shock.…”

In vivo measurement of signaling cascade dynamics

“…Furthermore, the Sho1 branch in many fungi does not seem to be connected to Pbs2 homologues nor involved in responding to osmotic stress. [23][24][25] …”