Row1, a member of a new family of conserved fungal proteins involved in infection, is required for appressoria functionality in Ustilago maydis.

The appressorium of phytopathogenic fungi is a specific structure with a crucial role in plant cuticle penetration. Pathogens with melanized appressoria break the cuticle through cell wall melanization and intracellular turgor pressure. However, in fungi with nonmelanized appressorium, the mechanisms governing cuticle penetration are poorly understood. Here we characterize Row1, a previously uncharacterized appressoria-specific protein of Ustilago maydis that localizes to membrane and secretory vesicles. Deletion of row1 decreases appressoria formation and plant penetration, thereby reducing virulence. Specifically, the Δrow1 mutant has a thicker cell wall that is more resistant to glucanase degradation. We also observed that the Δrow1 mutant has secretion defects. We show that Row1 is functionally conserved at least among Ustilaginaceae and belongs to the Row family, which consists of five other proteins that are highly conserved among Basidiomycota fungi and are involved in U. maydis virulence. We observed similarities in localization between Row1 and Row2, which is also involved in cell wall remodelling and secretion, suggesting similar molecular functions for members of this protein family. Our data suggest that Row1 could modify the chitin-glucan matrix of the fungal cell wall and may be involved in unconventional protein secretion, thereby promoting both appressoria maturation and penetration.

Surface Plasmon Resonance as a Tool to Elucidate the Molecular Determinants of Key Transcriptional Regulators Controlling Rhizobial Lifestyles.

Bacteria must be provided with a battery of tools integrated into regulatory networks, in order to respond and, consequently, adapt their physiology to changing environments. Within these networks, transcription factors finely orchestrate the expression of genes in response to a variety of signals, by recognizing specific DNA sequences at their promoter regions. Rhizobia are host-interacting soil bacteria that face severe changes to adapt their physiology from free-living conditions to the nitrogen-fixing endosymbiotic state inside root nodules associated with leguminous plants. One of these cues is the low partial pressure of oxygen within root nodules.Surface plasmon resonance (SPR) constitutes a technique that allows to measure molecular interactions dynamics at real time by detecting changes in the refractive index of a surface. Here, we implemented the SPR methodology to analyze the discriminatory determinants of transcription factors for specific interaction with their target genes. We focused on FixK2, a CRP/FNR-type protein with a central role in the complex oxygen-responsive regulatory network in the soybean endosymbiont Bradyrhizobium diazoefficiens. Our study unveiled relevant residues for protein-DNA interaction as well as allowed us to monitor kinetics and stability protein-DNA complex. We believe that this approach can be employed for the characterization of other relevant transcription factors which can assist to the better understanding of the adaptation of bacteria with agronomic or human interest to their different modes of life.

Fine-Tuning Modulation of Oxidation-Mediated Posttranslational Control of Bradyrhizobium diazoefficiens FixK2 Transcription Factor.

FixK2 is a CRP/FNR-type transcription factor that plays a central role in a sophisticated regulatory network for the anoxic, microoxic and symbiotic lifestyles of the soybean endosymbiont Bradyrhizobium diazoefficiens. Aside from the balanced expression of the fixK2 gene under microoxic conditions (induced by the two-component regulatory system FixLJ and negatively auto-repressed), FixK2 activity is posttranslationally controlled by proteolysis, and by the oxidation of a singular cysteine residue (C183) near its DNA-binding domain. To simulate the permanent oxidation of FixK2, we replaced C183 for aspartic acid. Purified C183D FixK2 protein showed both low DNA binding and in vitro transcriptional activation from the promoter of the fixNOQP operon, required for respiration under symbiosis. However, in a B. diazoefficiens strain coding for C183D FixK2, expression of a fixNOQP'-'lacZ fusion was similar to that in the wild type, when both strains were grown microoxically. The C183D FixK2 encoding strain also showed a wild-type phenotype in symbiosis with soybeans, and increased fixK2 gene expression levels and FixK2 protein abundance in cells. These two latter observations, together with the global transcriptional profile of the microoxically cultured C183D FixK2 encoding strain, suggest the existence of a finely tuned regulatory strategy to counterbalance the oxidation-mediated inactivation of FixK2 in vivo.

Optimized CRISPR-RfxCas13d system for RNA targeting in zebrafish embryos.

CRISPR-Cas systems have been used to induce DNA mutagenesis for gene function discovery. However, the development of tools to eliminate RNAs provides complementary and unique approaches to disrupt gene expression. Here, we present a workflow to perform specific, efficient, and cost-effective mRNA knockdown in zebrafish embryos using our in vivo optimized CRISPR-RfxCas13d (CasRx) system. Although the described protocol focuses on mRNA knockdown in zebrafish embryos, it can also be applied to other vertebrates. For complete details on the use and execution of this protocol, please refer to Kushawah et al. (2020).

Dissection of FixK2 protein-DNA interaction unveils new insights into Bradyrhizobium diazoefficiens lifestyles control.

The FixK2 protein plays a pivotal role in a complex regulatory network, which controls genes for microoxic, denitrifying, and symbiotic nitrogen-fixing lifestyles in Bradyrhizobium diazoefficiens. Among the microoxic-responsive FixK2 -activated genes are the fixNOQP operon, indispensable for respiration in symbiosis, and the nnrR regulatory gene needed for the nitric-oxide dependent induction of the norCBQD genes encoding the denitrifying nitric oxide reductase. FixK2 is a CRP/FNR-type transcription factor, which recognizes a 14 bp-palindrome (FixK2 box) at the regulated promoters through three residues (L195, E196, and R200) within a C-terminal helix-turn-helix motif. Here, we mapped the determinants for discriminatory FixK2 -mediated regulation. While R200 was essential for DNA binding and activity of FixK2 , L195 was involved in protein-DNA complex stability. Mutation at positions 1, 3, or 11 in the genuine FixK2 box at the fixNOQP promoter impaired transcription activation by FixK2 , which was residual when a second mutation affecting the box palindromy was introduced. The substitution of nucleotide 11 within the NnrR box at the norCBQD promoter allowed FixK2 -mediated activation in response to microoxia. Thus, position 11 within the FixK2 /NnrR boxes constitutes a key element that changes FixK2 targets specificity, and consequently, it might modulate B. diazoefficiens lifestyle as nitrogen fixer or as denitrifier.

CRISPR-Cas13d Induces Efficient mRNA Knockdown in Animal Embryos.

Early embryonic development is driven exclusively by maternal gene products deposited into the oocyte. Although critical in establishing early developmental programs, maternal gene functions have remained elusive due to a paucity of techniques for their systematic disruption and assessment. CRISPR-Cas13 systems have recently been employed to degrade RNA in yeast, plants, and mammalian cell lines. However, no systematic study of the potential of Cas13 has been carried out in an animal system. Here, we show that CRISPR-RfxCas13d (CasRx) is an effective and precise system to deplete specific mRNA transcripts in zebrafish embryos. We demonstrate that zygotically expressed and maternally provided transcripts are efficiently targeted, resulting in a 76% average decrease in transcript levels and recapitulation of well-known embryonic phenotypes. Moreover, we show that this system can be used in medaka, killifish, and mouse embryos. Altogether, our results demonstrate that CRISPR-RfxCas13d is an efficient knockdown platform to interrogate gene function in animal embryos.

The CbrB Regulon: Promoter dissection reveals novel insights into the CbrAB expression network in Pseudomonas putida.

CbrAB is a high ranked global regulatory system exclusive of the Pseudomonads that responds to carbon limiting conditions. It has become necessary to define the particular regulon of CbrB and discriminate it from the downstream cascades through other regulatory components. We have performed in vivo binding analysis of CbrB in P. putida and determined that it directly controls the expression of at least 61 genes; 20% involved in regulatory functions, including the previously identified CrcZ and CrcY small regulatory RNAs. The remaining are porines or transporters (20%), metabolic enzymes (16%), activities related to protein translation (5%) and orfs of uncharacterised function (38%). Amongst the later, we have selected the operon PP2810-13 to make an exhaustive analysis of the CbrB binding sequences, together with those of crcZ and crcY. We describe the implication of three independent non-palindromic subsites with a variable spacing in three different targets; CrcZ, CrcY and operon PP2810-13 in the CbrAB activation. CbrB is a quite peculiar σN-dependent activator since it is barely dependent on phosphorylation for transcriptional activation. With the depiction of the precise contacts of CbrB with the DNA, the analysis of the multimerisation status and its dependence on other factors such as RpoN o IHF, we propose a model of transcriptional activation.

Searching for a Cell-Based Therapeutic Tool for Haemophilia A within the Embryonic/Foetal Liver and the Aorta-Gonads-Mesonephros Region.

The development of new strategies based on cell therapy approaches to correct haemophilia A (HA) requires further insights into new cell populations capable of producing coagulation factor VIII (FVIII) and presenting stable engraftment potential. The major producers of FVIII in the adult are liver sinusoidal endothelial cells (LSECs) and in a lesser degree bone marrow-derived cells, both of which have been shown to ameliorate the bleeding phenotype in adult HA mice after transplantation. We have previously shown that cells from the foetal liver (FL) and the aorta-gonads-mesonephros (AGM) haematopoietic locations possess higher LSEC engraftment potential in newborn mice compared with adult-derived LSECs, constituting likely therapeutic targets for the treatment of HA in neonates. However, less is known about the production of FVIII in embryonic locations. Quantitative polymerase chain reaction and Western blot analysis were performed to assess the relative level of FVIII production in different embryonic tissues and at various developmental stages, identifying the FL and AGM region from day 12 (E12) as prominent sources of FVIII. Furthermore, FL-derived VE-cad+CD45-Lyve1+/- endothelial/endothelial progenitor cells, presenting vascular engraftment potential, produced high levels of F8 ribonucleic acid compared with CD45+ blood progenitors or Dlk1+ hepatoblasts. In addition, we show that the E11 AGM explant cultures expanded cells with LSEC repopulation activity, instrumental to further understand signals for in vitro generation of LSECs. Taking into account the capacity for FVIII expression, culture expansion and newborn engraftment potential, these results support the use of cells with foetal characteristics for correction of FVIII deficiency in young individuals.

Mechanism of Antiactivation at the Pseudomonas sp. Strain ADP σN-Dependent PatzT Promoter.

UNLABELLED: PatzT is an internal promoter of the atzRSTUVW operon that directs the synthesis of AtzT, AtzU, AtzV, and AtzW, components of an ABC-type cyanuric acid transport system. PatzT is σ(N) dependent, activated by the general nitrogen control regulator NtrC with the assistance of protein integration host factor (IHF), and repressed by the LysR-type transcriptional regulator (LTTR) AtzR. We have used a variety of in vivo and in vitro gene expression and protein-DNA interaction assays to assess the mechanisms underlying AtzR-dependent repression of PatzT Here, we show that repression only occurs when AtzR and NtrC interact simultaneously with the PatzT promoter region, indicating that AtzR acts as an antiactivator to antagonize activation by NtrC. Furthermore, repression requires precise rotational orientation of the AtzR and NtrC binding sites, strongly suggesting protein-protein interaction between the two proteins on the promoter region. Further exploration of the antiactivation mechanism showed that although AtzR-dependent repression occurs prior to open complex formation, AtzR does not alter the oligomerization state of NtrC or inhibit NtrC ATPase activity when bound to the PatzT promoter region. Taken together, these results strongly suggest that PatzT-bound AtzR interacts with NtrC to prevent the coupling of NtrC-mediated ATP hydrolysis with the remodeling of the interactions between E-σ(N) and PatzT that lead to open complex formation. IMPORTANCE: Here, we describe a unique mechanism by which the regulatory protein AtzR prevents the activation of the σ(N)-dependent promoter PatzT Promoters of this family are always positively regulated, but there are a few examples of overlapping negative regulation. The mechanism described here is highly unconventional and involves an interaction between the repressor and activator proteins to prevent the action of the repressor protein on the RNA polymerase-promoter complex.

ECM-Regulator timp Is Required for Stem Cell Niche Organization and Cyst Production in the Drosophila Ovary.

The extracellular matrix (ECM) is a pivotal component adult tissues and of many tissue-specific stem cell niches. It provides structural support and regulates niche signaling during tissue maintenance and regeneration. In many tissues, ECM remodeling depends on the regulation of MMP (matrix metalloproteinase) activity by inhibitory TIMP (tissue inhibitors of metalloproteinases) proteins. Here, we report that the only Drosophila timp gene is required for maintaining the normal organization and function of the germline stem cell niche in adult females. timp mutant ovaries show reduced levels of both Drosophila Collagen IV α chains. In addition, tissue stiffness and the cellular organization of the ovarian niche are affected in timp mutants. Finally, loss of timp impairs the ability of the germline stem cell niche to generate new cysts. Our results demonstrating a crucial role for timp in tissue organization and gamete production thus provide a link between the regulation of ECM metabolism and tissue homeostasis.

Proteome-wide search for PP2A substrates in fission yeast.

PP2A (protein phosphatase 2A) is a major phosphatase in eukaryotic cells that plays an essential role in many processes. PP2A mutations in Schizosaccharomyces pombe result in defects of cell cycle control, cytokinesis and morphogenesis. Which PP2A substrates are responsible for these changes is not known. In this work, we searched for PP2A substrates in S. pombe using two approaches, 2D-DIGE analysis of PP2A complex mutants and identification of PP2A interacting proteins. In both cases, we used MS to identify proteins of interest. In the DIGE experiment, we compared proteomes of wild-type S. pombe, deletion of pta2, the phosphoactivator of the PP2A catalytic subunit, and pab1-4, a mutant of B-type PP2A regulatory subunit. A total of 1742 protein spots were reproducibly resolved by 2D-DIGE and 51 spots demonstrated significant changes between PP2A mutants and the wild-type control. MS analysis of these spots identified 27 proteins that include key regulators of glycerol synthesis, carbon metabolism, amino acid biosyntesis, vitamin production, and protein folding. Importantly, we independently identified a subset of these proteins as PP2A binding partners by affinity precipitation, suggesting they may be direct targets of PP2A. We have validated our approach by demonstrating that phosphorylation of Gpd1, a key enzyme in glycerol biogenesis, is regulated by PP2A and that ability of cells to respond to osmotic stress by synthesizing glycerol is compromised in the PP2A mutants. Our work contributes to a better understanding of PP2A function and identifies potential PP2A substrates.

Combination of degradation pathways for naphthalene utilization in Rhodococcus sp. strain TFB.

Rhodococcus sp. strain TFB is a metabolic versatile bacterium able to grow on naphthalene as the only carbon and energy source. Applying proteomic, genetic and biochemical approaches, we propose in this paper that, at least, three coordinated but independently regulated set of genes are combined to degrade naphthalene in TFB. First, proteins involved in tetralin degradation are also induced by naphthalene and may carry out its conversion to salicylaldehyde. This is the only part of the naphthalene degradation pathway showing glucose catabolite repression. Second, a salicylaldehyde dehydrogenase activity that converts salicylaldehyde to salicylate is detected in naphthalene-grown cells but not in tetralin- or salicylate-grown cells. Finally, we describe the chromosomally located nag genes, encoding the gentisate pathway for salicylate conversion into fumarate and pyruvate, which are only induced by salicylate and not by naphthalene. This work shows how biodegradation pathways in Rhodococcus sp. strain TFB could be assembled using elements from different pathways mainly because of the laxity of the regulatory systems and the broad specificity of the catabolic enzymes.

Chaperoned amyloid proteins for immune manipulation: α-Synuclein/Hsp70 shifts immunity toward a modulatory phenotype.

α-Synuclein (αSyn) is a 140-residue amyloid-forming protein whose aggregation is linked to Parkinson's disease (PD). It has also been found to play a critical role in the immune imbalance that accompanies disease progression, a characteristic that has prompted the search for an effective αSyn-based immunotherapy. In this study, we have simultaneously exploited two important features of certain heat-shock proteins (HSPs): their classical "chaperone" activities and their recently discovered and diverse "immunoactive" properties. In particular, we have explored the immune response elicited by immunization of C57BL/6 mice with an αSyn/Hsp70 protein combination in the absence of added adjuvant. Our results show differential effects for mice immunized with the αSyn/Hsp70 complex, including a restrained αSyn-specific (IgM and IgG) humoral response as well as minimized alterations in the Treg (CD4(+)CD25(+)Foxp3(+)) and Teff (CD4(+)Foxp3(-)) cell populations, as opposed to significant changes in mice immunized with αSyn and Hsp70 alone. Furthermore, in vitro-stimulated splenocytes from immunized mice showed the lowest relative response against αSyn challenge for the "αSyn/Hsp70" experimental group as measured by IFN-γ and IL-17 secretion, and higher IL-10 levels when stimulated with LPS. Finally, serum levels of Th1-cytokine IFN-γ and immunomodulatory IL-10 indicated a unique shift toward an immunomodulatory/immunoprotective phenotype in mice immunized with the αSyn/Hsp70 complex. Overall, we propose the use of functional "HSP-chaperoned amyloid/aggregating proteins" generated with appropriate HSP-substrate protein combinations, such as the αSyn/Hsp70 complex, as a novel strategy for immune-based intervention against synucleinopathies and other amyloid or "misfolding" neurodegenerative disorders.

Involvement of a putative cyclic amp receptor protein (CRP)-like binding sequence and a CRP-like protein in glucose-mediated catabolite repression of thn genes in Rhodococcus sp. strain TFB.

Glucose catabolite repression of tetralin catabolic genes in Rhodococcus sp. strain TFB was shown to be exerted by a protein homologous to transcriptional regulators of the cyclic AMP receptor (CRP)-FNR family. The protein was detected bound to putative CRP-like boxes localized at the promoters of the thnA1 and thnS genes.

Molecular and biochemical characterization of the tetralin degradation pathway in Rhodococcus sp. strain TFB.

The tetralin biodegradation pathway in Rhodococcus sp. strain TFB, a Gram-positive bacterium resistant to genetic manipulation, was characterized using a proteomic approach. Relative protein expression in cell free extracts from tetralin- and glucose-grown cells was compared using the 2D-DIGE technique. Identification of proteins specifically expressed in tetralin-grown cells was used to characterize a complete set of genes involved in tetralin degradation by reverse genetics. We propose a tetralin degradation pathway analogous to that described for Sphingomonas macrogolitabida strain TFA. TFB thn genes are organized into three operons; two contain all of the structural genes and are transcribed in the same direction, while the third operon, thnST, is transcribed in the opposite direction and encodes a two-component regulatory system, whose transcription is higher in tetralin-grown cells. In addition to tetralin induction, TFB thn structural genes are subject to glucose repression. Primer extension assays and translational thnA1::gfp and thnS::gfp fusions were used to characterize putative promoter regions. A mutational analysis of the thnA1 promoter region allowed us to define nucleotides within the cis regulatory elements that are important for the control of thn gene expression.

Proteomic and transcriptional characterization of aromatic degradation pathways in Rhodoccocus sp. strain TFB.

Rhodococcus sp. strain TFB is a versatile gram-positive bacterium able to grow on a wide variety of aromatic compounds as carbon and energy sources. Since the strain is refractory to genetic analysis, a proteomic approach was used to study the metabolic pathways involved in the catabolism of such compounds by analyzing differentially induced proteins. The most marked difference was observed when the proteome profiles of phthalate-grown cells were compared with those cultured in the presence of tetralin- or naphthalene, suggesting that different metabolic pathways are involved in the degradation of mono- and polyaromatic compounds. Comparison with the proteome of glucose-grown cells indicated that each pathway was specifically induced by the corresponding aromatic compound. A combination of proteomics and molecular biology led to the identification of 14 proteins (65-80% identical to known Pht proteins) that describe a complete pathway for the catabolism of phthalate to central metabolites via intradiol cleavage of protochatechuic acid. Chaperonins were also induced in phthalate-grown cells, indicating that growth on this compound induces a stress response. Absence of catabolite repression by glucose was observed by both transcriptional and proteome analysis, suggesting that Rhodococcus sp. strain TFB may have advantages over other tightly regulated strains in bioremediation.