The moss Physcomitrella patens is becoming the model of choice for functional genomic studies at the cellular level. Studies report that Physcomitrella survives moderate osmotic and salt stress, and that desiccation tolerance can be induced by exogenous ABA. Our goal was to quantify the extent of dehydration tolerance in wild type moss and to examine the nature of cellular damage caused by desiccation. We exposed Physcomitrella to humidities that generate water potentials from -4 (97% RH) to -273 MPa (13% RH) and monitored water loss until equilibrium. Water contents were measured on a dry matter basis to determine the extent of dehydration because fresh weights (FW) were found to be variable and, therefore, unreliable. We measured electrolyte leakage from rehydrating moss, assessed overall regrowth, and imaged cells to evaluate their response to drying and rehydration. Physcomitrella did not routinely survive water potentials \-13 MPa. Upon rehydration, moss dried to water contents[0.4 g g dm -1 maintained levels of leakage similar to those of hydrated controls. Moss dried to lower water contents leaked extensively, suggesting that plasma membranes were damaged. Moss protonemal cells were shrunken and their walls twisted, even at -13 MPa. Moss cells rehydrated after drying to -273 MPa failed to re-expand completely, again indicating membrane damage. ABA treatment elicited tolerance of desiccation to at least -273 MPa and limited membrane damage. Results of this work will form the basis for ongoing studies on the functional genomics of desiccation tolerance at the cellular level.

SummaryChitin is the second most abundant polysaccharide in nature, found in crustacean shells, insect exoskeletons and fungal cell walls. The action of chitin and chitin derivatives on plants has become a very interesting story of late. Chitin is a b1-4-linked polymer of N-acetyl-Dglucosamine (GlcNAc). In this unmodified form, chitooligosaccharides (degree of polymerization (dp) = 6-8)) are strong inducers of plant innate immunity. By contrast, when these chitooligosaccharides are acylated (so-called lipochitooligosaccharides, LCOs) and further modified, they can act as Nod factors, the key signaling molecules that play an important role in the initiation of the legume-rhizobium symbiosis. In a similar form, these molecules can also act as Myc factors, the key signaling molecules involved in the arbuscular mycorrhizal (AM) symbiosis. It has been proposed that Nod factor perception might have evolved from the more ancient AM symbiosis. Increasing evidence now suggests that LCO perception might have evolved from plant innate immunity signaling. In this review, we will discuss the evolutionary origin of symbiotic LCO recognition.

Long-chain chitooligosaccharides are fungal microbe-associated molecular patterns (MAMPs) that are recognized by LYSIN MOTIF RECEPTOR KINASE5 (LYK5), inducing the formation of a complex with CHITIN ELICITOR RECEPTOR KINASE1 (CERK1). Formation of this complex leads to activation of the CERK1 intracellular kinase domain and induction of plant innate immunity in Arabidopsis. We found that addition of chitooctaose induced LYK5 protein accumulation as a result of de novo gene expression and the inhibition of LYK5 protein degradation. Screening the putative E3 ligases for interaction with LYK5 identified PLANT U-BOX13 (PUB13), which complexed with LYK5, but this complex dissociated upon addition of chitooctaose. Consistent with these results, LYK5 protein abundance was higher in pub13 mutants compared with the wild type without chitooctaose treatment, while similar abundance was detected with the addition of chitooctaose. The pub13 mutants showed hypersensitivity to chitooctaose-induced rapid responses, such as the production of reactive oxygen species (ROS) and mitogen-activated protein (MAP) kinase phosphorylation, but exhibited normal responses to subsequent long-term chitooctaose treatment, such as gene expression and callose deposition. In addition, PUB13 could ubiquitinate the LYK5 kinase domain in vitro. Taken together, our results suggest an important regulatory function for the turnover of LYK5 mediated by the E3 ligase PUB13.

BackgroundUnderstanding the response of resurrection angiosperms to dehydration and rehydration is critical for deciphering the mechanisms of how plants cope with the rigors of water loss from their vegetative tissues. We have focused our studies on the C4 resurrection grass, Sporobolus stapfianus Gandoger, as a member of a group of important forage grasses.MethodsWe have combined non-targeted metabolomics with transcriptomics, via a NimbleGen array platform, to develop an understanding of how gene expression and metabolite profiles can be linked to generate a more detailed mechanistic appreciation of the cellular response to both desiccation and rehydration.ResultsThe rehydration transcriptome and metabolome are primarily geared towards the rapid return of photosynthesis, energy metabolism, protein turnover, and protein synthesis during the rehydration phase. However, there are some metabolites associated with ROS protection that remain elevated during rehydration, most notably the tocopherols. The analysis of the dehydration transcriptome reveals a strong concordance between transcript abundance and the associated metabolite abundance reported earlier, but only in responses that are directly related to cellular protection during dehydration: carbohydrate metabolism and redox homeostasis. The transcriptome response also provides strong support for the involvement of cellular protection processes as exemplified by the increases in the abundance of transcripts encoding late embryogenesis abundant (LEA) proteins, anti-oxidant enzymes, early light-induced proteins (ELIP) proteins, and cell-wall modification enzymes. There is little concordance between transcript and metabolite abundance for processes such as amino acid metabolism that do not appear to contribute directly to cellular protection, but are nonetheless important for the desiccation tolerant phenotype of S. stapfianus.ConclusionsThe transcriptomes of both dehydration and rehydration offer insight into the complexity of the regulation of responses to these processes that involve complex signaling pathways and associated transcription factors. ABA appears to be important in the control of gene expression in both the latter stages of the dehydration and the early stages of rehydration. These findings add to the growing body of information detailing how plants tolerate and survive the severe cellular perturbations of dehydration, desiccation, and rehydration.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-017-1013-7) contains supplementary material, which is available to authorized users.