SENSITIVE TO FREEZING2 is crucial for growth of Marchantia polymorpha under acidic conditions.

Land plants have evolved many systems to adapt to a wide range of environmental stresses. In seed plants, oligogalactolipid synthesis is involved in tolerance to freezing and dehydration, but it has not been analyzed in non-vascular plants. Here we analyzed trigalactosyldiacylglycerol (TGDG) synthesis in Marchantia polymorpha. TGDG is synthesized by galactolipid: galactolipid galactosyltransferase [GGGT; SENSITIVE TO FREEZING2 (SFR2) in Arabidopsis]. We analyzed the subcellular localization and GGGT activity of two M. polymorpha SFR2 homologs (MpGGGT1 and MpGGGT2, each as a GFP-fusion protein) using a transient expression system in Nicotiana benthamiana leaves and found that MpGGGT1-GFP localized in the chloroplast envelope membrane. We produced mutants Mpgggt1 and Mpgggt2 and found that TGDG did not accumulate in Mpgggt1 upon treatment of the thallus with acetic acid. Moreover, growth of Mpgggt1 mutants was impaired by acetic acid treatment. Microscopy revealed that the acetic acid treatment of M. polymorpha plants damaged intracellular membranes. The fact that the effect was similar for wild-type and Mpgggt1 plants suggested that MpGGGT has a role in recovery from damage. These results indicate that MpGGGT plays a crucial role in M. polymorpha growth under conditions of acid stress, which may have been encountered during the ancient terrestrial colonization of plants.

Monitoring sodium caseinate and whey protein isolate interaction with mild preheat treatment using ultrasound spectroscopy and confocal laser scanning microscopy.

Ultrasound spectroscopy and confocal laser scanning microscopy (CLSM) methods were developed to visualize the interaction between sodium caseinate (SC) and whey protein isolate (WPI) with a mild preheat treatment (57°C, 10 min) followed by adding glucono-δ-lactone (GDL). Ultrasonic velocity changes during incubation at 25°C after adding GDL for four kinds of mixtures (no-treated SC plus no-treated WPI, preheated SC plus no-treated WPI, no-treated SC plus preheated WPI and preheated SC plus preheated WPI) were monitored. The results reveal that the mild preheating treatment of the proteins affected the timing of the increase in compressibility of each system. CLSM observation with individualized dyes which have different maxima of excitation and emission wavelengths, showed the preheated SC plus no-treated WPI mixture had a slightly coarse structure and the highest correlation coefficient, suggesting the highest colocalization of the SC and WPI among the four kinds of mixed-protein systems. Furthermore, the scanning electron microscopy (SEM) observation suggests that there are some differences among the gels, namely, preheated WPI leads to the formation of developed three-dimensional gel networks with filamentous structures, whereas SC promotes the formation of cluster-like crowded networks composed of more fine aggregated particles instead of developed filamentous structures. These results demonstrated that although SC is known as a heat-stable protein, pretreated SC could lead to an increase of the collaboration with WPI in the presence of GDL. This finding anticipated the possibility creating a food material with another texture using a milk-protein mixed system.

Phosphatidic acid phosphohydrolase modulates glycerolipid synthesis in Marchantia polymorpha and is crucial for growth under both nutrient-replete and -deficient conditions.

MAIN CONCLUSION: The phosphatidic acid phosphohydrolase of Marchantia polymorpha modulates plastid glycolipid synthesis through the ER pathway and is essential for normal plant development regardless of nutrient availability. Membrane lipid remodeling is one of the strategies plant cells use to secure inorganic phosphate (Pi) for plant growth, but many aspects of the molecular mechanism and its regulation remain unclear. Here we analyzed membrane lipid remodeling using a non-vascular plant, Marchantia polymorpha. The lipid composition and fatty acid profile during Pi starvation in M. polymorpha revealed a decrease in phospholipids and an increase in both galactolipids and betaine lipids. In Arabidopsis thaliana, phosphatidic acid phosphohydrolase (PAH) is involved in phospholipid degradation and is crucial for tolerance to both Pi and nitrogen starvation. We produced two M. polymorpha PAH (MpPAH) knockout mutants (Mppah-1 and Mppah-2) and found that, unlike Arabidopsis mutants, Mppah impaired plant growth with shorter rhizoids compared with wild-type plants even under nutrient-replete conditions. Mutation of MpPAH did not significantly affect the mole percent of each glycerolipid among total membrane glycerolipids from whole plants under both Pi-replete and Pi-deficient conditions. However, the fatty acid composition of monogalactosyldiacylglycerol indicated that the amount of plastid glycolipids produced through the endoplasmic reticulum pathway was suppressed in Mppah mutants. Phospholipids accumulated in the mutants under N starvation. These results reveal that MpPAH modulates plastid glycolipid synthesis through the endoplasmic reticulum pathway more so than what has been observed for Arabidopsis PAH; moreover, unlike Arabidopsis, MpPAH is crucial for M. polymorpha growth regardless of nutrient availability.

Cis-regulatory elements and transcription factors related to auxin signaling in the streptophyte algae Klebsormidium nitens.

The phytohormone auxin affects numerous processes in land plants. The central auxin signaling machinery, called the nuclear auxin pathway, is mediated by its pivotal receptor named TRANSPORT INHIBITOR RESPONSE 1/AUXIN SIGNALING F-BOX (TIR1/AFB). The nuclear auxin pathway is widely conserved in land plants, but auxin also accumulates in various algae. Although auxin affects the growth of several algae, the components that mediate auxin signaling have not been identified. We previously reported that exogenous auxin suppresses cell proliferation in the Klebsormidium nitens that is a member of streptophyte algae, a paraphyletic group sharing the common ancestor with land plants. Although K. nitens lacks TIR1/AFB, auxin affects the expression of numerous genes. Thus, elucidation of the mechanism of auxin-inducible gene expression in K. nitens would provide important insights into the evolution of auxin signaling. Here, we show that some motifs are enriched in the promoter sequences of auxin-inducible genes in K. nitens. We also found that the transcription factor KnRAV activates several auxin-inducible genes and directly binds the promoter of KnLBD1, a representative auxin-inducible gene. We propose that KnRAV has the potential to regulate auxin-responsive gene expression in K. nitens.

The Sulfide-Responsive SqrR/BigR Homologous Regulator YgaV of Escherichia coli Controls Expression of Anaerobic Respiratory Genes and Antibiotic Tolerance.

Compositions and activities of bacterial flora in the gastrointestinal tract significantly influence the metabolism, health, and disease of host humans and animals. These enteric bacteria can switch between aerobic and anaerobic growth if oxygen tension becomes limited. Interestingly, the switching mechanism is important for preventing reactive oxygen species (ROS) production and antibiotic tolerance. Studies have also shown that intracellular and extracellular sulfide molecules are involved in this switching control, although the mechanism is not fully clarified. Here, we found that YgaV, a sulfide-responsive transcription factor SqrR/BigR homolog, responded to sulfide compounds in vivo and in vitro to control anaerobic respiratory gene expression. YgaV also responded to H2O2 scavenging in the enteric bacterium Escherichia coli. Although the wild-type (WT) showed increased antibiotic tolerance under H2S-atmospheric conditions, the ygaV mutant did not show such a phenotype. Additionally, antibiotic sensitivity was higher in the mutant than in the WT of both types in the presence and absence of exogenous H2S. These results, therefore, indicated that YgaV-dependent transcriptional regulation was responsible for maintaining redox homeostasis, ROS scavenging, and antibiotic tolerance.

Characterization of the gelation and resulting network of a mixed-protein gel derived from sodium caseinate and ovalbumin in the presence of glucono-δ-lactone.

We investigated mixed-protein gels made from sodium caseinate and ovalbumin at different ratios with use of the acidification agent glucono-δ-lactone. Dynamic viscoelastic measurements revealed that increasing the ovalbumin content decreased the mechanical properties of the gel but accelerated onset time of the phase transition. Ultrasound spectroscopy during gelation revealed that the relative velocity gradually decreased, whereas the ultrasonic attenuation increased during the whole acidification process until gelation was complete, although these changes were much smaller than those observed with heat-induced gelation. Confocal laser scanning microscopy along with scanning electron microscopy revealed that although uniform mixing of sodium caseinate and ovalbumin was observed, sodium caseinate is likely to mainly lead formation of the gel network, and the porosity of the resulting gel network depends on the ratio of these two components. The results demonstrate that confocal laser scanning microscopy is a useful tool for analyzing both the networks within mixed-protein gels and the contribution of each protein to the network and gelation.

MYB-like transcription factor NoPSR1 is crucial for membrane lipid remodeling under phosphate starvation in the oleaginous microalga Nannochloropsis oceanica.

Membrane lipid remodeling under phosphate (Pi) limitation, a process that replaces structural membrane phospholipids with nonphosphorus lipids, is a widely observed adaptive response in plants and algae. Here, we identified the transcription factor phosphorus starvation response 1 (NoPSR1) as an indispensable player for regulating membrane lipid conversion during Pi starvation in the microalga Nannochloropsis oceanica. Knocking out NoPSR1 scarcely perturbed membrane lipid composition under Pi-sufficient conditions but significantly impaired dynamic alteration in membrane lipids during Pi starvation. In contrast, the absence of NoPSR1 led to no obvious change in cell proliferation or storage lipid accumulation under either nutrient-sufficient or Pi-deficient conditions. Our results demonstrate a key factor controlling the membrane lipid profile during the Pi starvation response in N. oceanica.

Lipid remodeling regulator 1 (LRL1) is differently involved in the phosphorus-depletion response from PSR1 in Chlamydomonas reinhardtii.

The elucidation of lipid metabolism in microalgae has attracted broad interest, as their storage lipid, triacylglycerol (TAG), can be readily converted into biofuel via transesterification. TAG accumulates in the form of oil droplets, especially when cells undergo nutrient deprivation, such as for nitrogen (N), phosphorus (P), or sulfur (S). TAG biosynthesis under N-deprivation has been comprehensively studied in the model microalga Chlamydomonas reinhardtii, during which TAG accumulates dramatically. However, the resulting rapid breakdown of chlorophyll restricts overall oil yield productivity and causes cessation of cell growth. In contrast, P-deprivation results in oil accumulation without disrupting chloroplast integrity. We used a reverse genetics approach based on co-expression analysis to identify a transcription factor (TF) that is upregulated under P-depleted conditions. Transcriptomic analysis revealed that the mutants showed repression of genes typically associated with lipid remodeling under P-depleted conditions, such as sulfoquinovosyl diacylglycerol 2 (SQD2), diacylglycerol acyltransferase (DGTT1), and major lipid droplet protein (MLDP). As accumulation of sulfoquinovosyl diacylglycerol and TAG were suppressed in P-depleted mutants, we designated the protein as lipid remodeling regulator 1 (LRL1). LRL1 mutants showed slower growth under P-depletion. Moreover, cell size in the mutant was significantly reduced, and TAG and starch accumulation per cell were decreased. Transcriptomic analysis also suggested the repression of several genes typically upregulated in adaptation to P-depletion that are associated with the cell cycle and P and lipid metabolism. Thus, our analysis of LRL1 provides insights into P-allocation and lipid remodeling under P-depleted conditions in C. reinhardtii. OPEN RESEARCH BADGES: This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The sequencing data were made publicly available under the BioProject Accession number PRJDB6733 and an accession number LC488724 at the DNA Data Bank of Japan (DDBJ). The data is available at https://trace.ddbj.nig.ac.jp/BPSearch/bioproject?acc=PRJDB6733; http://getentry.ddbj.nig.ac.jp/getentry/na/LC488724. The metabolome data were made publicly available and can be accessed at http://metabolonote.kazusa.or.jp/SE195:/; http://webs2.kazusa.or.jp/data/nur/.

Erratum: Publisher Correction: SnRK2 protein kinases represent an ancient system in plants for adaptation to a terrestrial environment.

[This corrects the article DOI: 10.1038/s42003-019-0281-1.].

SnRK2 protein kinases represent an ancient system in plants for adaptation to a terrestrial environment.

The SNF1-related protein kinase 2 (SnRK2) family includes key regulators of osmostress and abscisic acid (ABA) responses in angiosperms and can be classified into three subclasses. Subclass III SnRK2s act in the ABA response while ABA-nonresponsive subclass I SnRK2s are regulated through osmostress. Here we report that an ancient subclass III SnRK2-based signalling module including ABA and an upstream Raf-like kinase (ARK) exclusively protects the moss Physcomitrella patens from drought. Subclass III SnRK2s from both Arabidopsis and from the semiterrestrial alga Klebsormidium nitens, which contains all the components of ABA signalling except ABA receptors, complement Physcomitrella snrk2 - mutants, whereas Arabidopsis subclass I SnRK2 cannot. We propose that the earliest land plants developed the ABA/ARK/subclass III SnRK2 signalling module by recruiting ABA to regulate a pre-existing dehydration response and that subsequently a novel subclass I SnRK2 system evolved in vascular plants conferring osmostress protection independently from the ancient system.