The role of the novel adenosine 5'-phosphosulfate reductase in regulation of sulfate assimilation of Physcomitrella patens

Transcriptomic analysis of salt stress induced chlorophyll biosynthesis-related genes in photoheterotrophic Arabidopsis thaliana calli

In order to investigate the salt stress induced chlorophyll biosynthesis-related genes in photoheterotrophic cultures, we performed RNA-Seq analysis on A. thaliana calli exposed to 100 mM NaCl on MS medium containing 0.5 mg/L 2,4-D 30 days. Four different conditions of samples were sequenced on Illumina HiSeq Platform in total and generated about 4.49 Gb per sample. The average genome and gene mapping rates were 93.52% and 90.78%, respectively. According to expression profile analysis, some DEGs demonstrated altered related to chlorophyll pigment metabolism. According to analysis, green callus color of photoheterotrophic calli were mainly connected with the induction of LHCB4.3 light harvesting complex photosystem II (Gene ID:818599), AT1G49975 photosystem I reaction center subunit N (Gene ID: 841421), PAM68 PAM68-like protein (DUF3464) (Gene ID: 2745715) and AT3G63540 thylakoid lumenal protein (Mog1/PsbP/DUF1795-like photosystem II reaction center PsbP family protein)(Gene ID: 7922413) genes. Furthermore, 8 DEGs were randomly selected to validate the transcriptome profiles via qPCR. These results will provide a foundation for further studies aimed at giving photosynthetic properties to in vitro plant cultures.

Spatio-temporal patterning of arginyl-tRNA protein transferase (ATE) contributes to gametophytic development in a moss

The importance of the arginyl-tRNA protein transferase (ATE), the enzyme mediating post-translation arginylation of proteins in the N-end rule degradation (NERD) pathway of protein stability, was analysed in Physcomitrella patens and compared to its known functions in other eukaryotes. We characterize ATE:GUS reporter lines as well as ATE mutants in P. patens to study the impact and function of arginylation on moss development and physiology. ATE protein abundance is spatially and temporally regulated in P. patens by hormones and light and is highly abundant in meristematic cells. Further, the amount of ATE transcript is regulated during abscisic acid signalling and downstream of auxin signalling. Loss-of-function mutants exhibit defects at various levels, most severely in developing gametophores, in chloroplast starch accumulation and senescence. Thus, arginylation is necessary for moss gametophyte development, in contrast to the situation in flowering plants. Our analysis further substantiates the conservation of the N-end rule pathway components in land plants and highlights lineage-specific features. We introduce moss as a model system to characterize the role of the NERD pathway as an additional layer of complexity in eukaryotic development.

Gene Targeting for Precision Glyco-Engineering: Production of Biopharmaceuticals Devoid of Plant-Typical Glycosylation in Moss Bioreactors

One of the main challenges for the production of biopharmaceuticals in plant-based systems is the modulation of plant-specific glycosylation patterns towards a humanized form. Posttranslational modifications in plants are similar to those in humans, but several differences affect product quality and efficacy and can also cause immune responses in patients. In the moss Physcomitrella patens highly efficient gene targeting via homologous recombination enables glyco-engineering to obtain suitable platform lines for the production of recombinant proteins and biopharmaceuticals. Here we describe the methods which are effective for creating gene targeting constructs and transgenic moss lines as well as confirming successful homologous integration of the constructs and modification of target gene expression.

The relevance of compartmentation for cysteine synthesis in phototrophic organisms

In the vascular plant Arabidopsis thaliana, synthesis of cysteine and its precursors O-acetylserine and sulfide is distributed between the cytosol, chloroplasts, and mitochondria. This compartmentation contributes to regulation of cysteine synthesis. In contrast to Arabidopsis, cysteine synthesis is exclusively restricted to chloroplasts in the unicellular green alga Chlamydomonas reinhardtii. Thus, the question arises, whether specification of compartmentation was driven by multicellularity and specified organs and tissues. The moss Physcomitrella patens colonizes land but is still characterized by a simple morphology compared to vascular plants. It was therefore used as model organism to study evolution of compartmented cysteine synthesis. The presence of O-acetylserine(thiol)lyase (OAS-TL) proteins, which catalyze the final step of cysteine synthesis, in different compartments was applied as criterion. Purification and characterization of native OAS-TL proteins demonstrated the presence of five OAS-TL protein species encoded by two genes in Physcomitrella. At least one of the gene products is dual targeted to plastids and cytosol, as shown by combination of GFP fusion localization studies, purification of chloroplasts, and identification of N termini from native proteins. The bulk of OAS-TL protein is targeted to plastids, whereas there is no evidence for a mitochondrial OAS-TL isoform and only a minor part of OAS-TL protein is localized in the cytosol. This demonstrates that subcellular diversification of cysteine synthesis is already initialized in Physcomitrella but appears to gain relevance later during evolution of vascular plants.

Control of sulfur partitioning between primary and secondary metabolism

Sulfur is an essential nutrient for all organisms. Plants take up most sulfur as inorganic sulfate, reduce it and incorporate it into cysteine during primary sulfate assimilation. However, some of the sulfate is partitioned into the secondary metabolism to synthesize a variety of sulfated compounds. The two pathways of sulfate utilization branch after activation of sulfate to adenosine 5'-phosphosulfate (APS). Recently we showed that the enzyme APS kinase limits the availability of activated sulfate for the synthesis of sulfated secondary compounds in Arabidopsis. To further dissect the control of sulfur partitioning between the primary and secondary metabolism, we analysed plants in which activities of enzymes that use APS as a substrate were increased or reduced. Reduction in APS kinase activity led to reduced levels of glucosinolates as a major class of sulfated secondary metabolites and an increased concentration of thiols, products of primary reduction. However, over-expression of this gene does not affect the levels of glucosinolates. Over-expression of APS reductase had no effect on glucosinolate levels but did increase thiol levels, but neither glucosinolate nor thiol levels were affected in mutants lacking the APR2 isoform of this enzyme. Measuring the flux through sulfate assimilation using [(35) S]sulfate confirmed the larger flow of sulfur to primary assimilation when APS kinase activity was reduced. Thus, at least in Arabidopsis, the interplay between APS reductase and APS kinase is important for sulfur partitioning between the primary and secondary metabolism.

Regulation of sulfate assimilation in Physcomitrella patens: mosses are different!

Sulfur is an essential nutrient, taken up as sulfate from soil, reduced and incorporated into bioorganic compounds in plant cells. The pathway of sulfate assimilation is highly regulated in a demand-driven manner in seed plants. To test the evolutionary conservation of the regulatory mechanisms, we analyzed regulation of the pathway in the model for basal plants, the moss Physcomitrella patens. While in Arabidopsis the key enzyme of sulfate assimilation, adenosine 5'-phosphosulfate reductase (APR), is feedback repressed by thiols and induced by reduced levels of glutathione, in P. patens such regulation does not occur. The control of the pathway was not moved to other components as these conditions affected neither mRNA accumulation of other genes of sulfate assimilation nor sulfate uptake. Other treatments known to regulate APR, O-acetylserine, cadmium and sulfur deficiency affected APR transcript levels, but not enzyme activity. It appears that the sulfate assimilation pathway in P. patens is much more robust than in seed plants. Thus, the regulatory networks controlling the pathway have probably evolved only later in the evolution of the seed plants after separation of the bryophytes.

The molecular and physiological responses of Physcomitrella patens to ultraviolet-B radiation

Ultraviolet-B (UV-B) radiation present in sunlight is an important trigger of photomorphogenic acclimation and stress responses in sessile land plants. Although numerous moss species grow in unshaded habitats, our understanding of their UV-B responses is very limited. The genome of the model moss Physcomitrella patens, which grows in sun-exposed open areas, encodes signaling and metabolic components that are implicated in the UV-B response in flowering plants. In this study, we describe the response of P. patens to UV-B radiation at the morphological and molecular levels. We find that P. patens is more capable of surviving UV-B stress than Arabidopsis (Arabidopsis thaliana) and describe the differential expression of approximately 400 moss genes in response to UV-B radiation. A comparative analysis of the UV-B response in P. patens and Arabidopsis reveals both distinct and conserved pathways.

Targeted knock-out of a gene encoding sulfite reductase in the moss Physcomitrella patens affects gametophytic and sporophytic development

A key step in sulfate assimilation into cysteine is the reduction of sulfite to sulfide by sulfite reductase (SiR). This enzyme is encoded by three genes in the moss Physcomitrella patens. To obtain a first insight into the roles of the individual isoforms, we deleted the gene encoding the SiR1 isoform in P. patens by homologous recombination and subsequently analysed the DeltaSiR1 mutants. While DeltaSiR1 mutants showed no obvious alteration in sulfur metabolism, their regeneration from protoplasts and their ability to produce mature spores was significantly affected, highlighting an unexpected link between moss sulfate assimilation and development, that is yet to be characterized.

Plant sulfate assimilation genes: redundancy versus specialization

Sulfur is an essential nutrient present in the amino acids cysteine and methionine, co-enzymes and vitamins. Plants and many microorganisms are able to utilize inorganic sulfate and assimilate it into these compounds. Sulfate assimilation in plants has been extensively studied because of the many functions of sulfur in plant metabolism and stress defense. The pathway is highly regulated in a demand-driven manner. A characteristic feature of this pathway is that most of its components are encoded by small multigene families. This may not be surprising, as several steps of sulfate assimilation occur in multiple cellular compartments, but the composition of the gene families is more complex than simply organellar versus cytosolic forms. Recently, several of these gene families have been investigated in a systematic manner utilizing Arabidopsis reverse genetics tools. In this review, we will assess how far the individual isoforms of sulfate assimilation enzymes possess specific functions and what level of genetic redundancy is retained. We will also compare the genomic organization of sulfate assimilation in the model plant Arabidopsis thaliana with other plant species to find common and species-specific features of the pathway.

Moss (Physcomitrella patens) GH3 proteins act in auxin homeostasis

Auxins are hormones involved in many cellular, physiological and developmental processes in seed plants and in mosses such as Physcomitrella patens. Control of auxin levels is achieved in higher plants via synthesis of auxin conjugates by members of the GH3 family. The role of the two GH3-like proteins from P. patens for growth and auxin homeostasis was therefore analysed. The in vivo-function of the two P. patens GH3 genes was investigated using single and double knockout mutants. The two P. patens GH3 proteins were also heterologously expressed to determine their enzymatic activity. Both P. patens GH3 enzymes accepted the auxin indole acetic acid (IAA) as substrate, but with different preferences for the amino acid to which it is attached. Cytoplasmic localization was shown for PpGH3-1 tagged with green fluorescent protein (GFP). Targeted knock-out of either gene exhibited an increased sensitivity to auxin, resulting in growth inhibition. On plain mineral media mutants had higher levels of free IAA and less conjugated IAA than the wild type, and this effect was enhanced when auxin was supplied. The DeltaPpGH3-1/DeltaPpGH3-2 double knockout had almost no IAA amide conjugates but still synthesized ester conjugates. Taken together, these data suggest a developmentally controlled involvement of P. patens GH3 proteins in auxin homeostasis by conjugating excess of physiologically active free auxin to inactive IAA-amide conjugates.