Desiccation Tolerance in Terrestrial Green Algae
In collaboration with Prof. Dr. A. Holzinger (Innsbruck University, Innsbruck, Austria, supported by the Wissenschaftsfond, Austria) we are investigating survival strategies of green algae in the extreme alpine environment with a focus on desiccation tolerance.
Desiccation tolerance in streptophyte algae is studied in collaboration with using alpine Klebsormidium and Zygnema species as green algal model systems. We have already shown that many streptophyte algae express homologues of late-embryo-abundant proteins (LEA proteins, Wodniok et al. 2011) which are important in seed plants for survival of the embryo during seed maturation. Recently we have now published the first results from Klebsormidium crenulatutum (Holzinger et al. 2014). Most of the highly up-regulated transcripts do not show similarity to known viridiplant proteins, suggesting the existence of some genus- or species-specific responses to desiccation. In addition, we observed the up-regulation of many transcripts involved in desiccation tolerance in plants (e.g. proteins similar to those that are abundant in late embryogenesis (LEA), or proteins involved in early response to desiccation ERD), and enzymes involved in the biosynthesis of the raffinose family of oligosaccharides (RFO) known to act as osmolytes). Major physiological shifts are the up-regulation of transcripts for photosynthesis, energy production, and reactive oxygen species (ROS) metabolism. Our results indicate that the cellular response of Klebsormidium is similar to embryophytes, suggesting that embryophytes inherited a basic cellular desiccation tolerance from their streptophyte predecessors. A recent further analysis of the role of phytohormones during desiccation stress, showed that again similar to embryophytes, desiccaton tolerance might be controled by the abcisic acid, cytokinine and ethylen signal transduction pathways (Holzinger & Becker 2015)
The observed up- and downregulation for the three pathways is different (up-or down-regulation, fold change in expression level). While these changes are interesting themselves, they do not represent direct evidence for phytohormone signaling in response to desiccation stress. Most interesting in this respect is the observed up-regulation of the single putative ortholog of type A ARR response regulators, which expression is under direct control of the cytokinin signaling pathway, suggesting that desiccation leads indeed to an activation of cytokinin signaling pathway in Klebsormidium crenulatum.