AURTHO: Autoregulation of transcription factors as facilitator of cis-acting element discovery

Genome-wide identification of pyrabactin resistance 1-like (PYL) gene family under phytohormones and drought stresses in alfalfa (Medicago sativa)

BACKGROUND

The Pyrabactin resistance 1-like proteins (PYR/PYL/RCAR) protein plays a critical regulatory role in the ABA signal transduction pathway as a direct receptor of abscisic acid (ABA). Although PYL genes have been identified in a variety of plants, the evolution and structural characteristics of these genes in alfalfa (Medicago sativa) are largely unknown. Therefore, a comprehensive bioinformatics analysis of the PYL gene family was performed in this research.

RESULTS

The results indicated that 41 MsPYL genes were unevenly distributed across 24 chromosomes. According to gene structure, conservative features, and phylogenetic relationships, MsPYL proteins can be divided into 6 groups, all of which have PYR/PYL/RCAR domains, and MsPYL proteins are relatively small (molecular weight 19.59 kDa to 25.31 kDa). MsPYL genes contains cis-acting elements that has functions in plant growth and development, hormone regulation, and stress response. Furthermore, transcriptome data showed that drought stress affected the MsPYL genes' expression levels in alfalfa. Tissue specificity analysis revealed that all MsPYL genes exhibited varying responses to drought, abscisic acid (ABA), salicylic acid (SA), and indole-3-acetic acid (IAA). Additionally, all MsPYL genes were expressed to different extents in both the aboveground and underground tissues following stimulation. They were induced by IAA, ABA, and SA from 6 h to 12 h, and ABA induced MsPYL4 most significantly at the 12 h mark. MsPYL4, MsPYL8, MsPYL11, and MsPYL19 were expressed only after hormone treatment.

CONCLUSIONS

The results of this study indicate that the MsPYL genes are closely related to stress response and provide new candidate genes for further exploration of MsPYL genes function and improvement and innovation of drought-resistant alfalfa germplasm.

Regulatory Genes as Beacons for Discovery and Prioritization of Biosynthetic Gene Clusters in Streptomyces

Actinobacteria are renowned for their ability to produce a wide range of bioactive molecules, including many anticancer compounds and antibiotics that are critical in the battle against antimicrobial resistance. Despite identification of a vast array of biosynthetic gene clusters (BGCs) through genome mining, much of this biosynthetic potential remains unexplored, partially due to the fact that many remain silent or cryptic under typical laboratory conditions. Regulatory networks can provide clues to the location of yet undiscovered gene cluster families or be leveraged to predict their expression. Here, we investigate the associations between regulatory genes and BGCs to uncover their predictive capabilities in discovering and prioritizing gene clusters for downstream wet-lab validation. By analyzing the protein domain architectures of 128,993 potential regulators derived from 440 complete Streptomyces genomes, we uncovered various associations between biosynthetic classes, biological activities of their products, and regulator families. Specifically, subsets of the Streptomyces Antibiotic Regulatory Protein (SARP) and LuxR families were strongly associated with biosynthetic pathways encoding the production of bioactive compounds. After closer genomic inspection of the small SARPs, we discovered 82 putative SARP-associated BGCs that escaped detection by state-of-the-art software. This shows that continued exploration of regulatory systems will not only deepen our understanding of Actinobacteria's biosynthetic capabilities but also facilitates discovery and prioritization of high-potential BGCs in future genome-mining applications.

Identification and characterization of archaeal pseudomurein biosynthesis genes through pangenomics

The peptidoglycan (PG, or murein) is a mesh-like structure, which is made of glycan polymers connected by short peptides and surrounds the cell membrane of nearly all bacterial species. In contrast, there is no PG counterpart that would be universally found in Archaea but rather various polymers that are specific to some lineages. Methanopyrales and Methanobacteriales are two orders of Euryarchaeota that harbor pseudomurein (PM), a structural analog of the bacterial PG. Owing to the differences between PG and PM biosynthesis, some have argued that the origin of both polymers is not connected. However, recent studies have revealed that the genomes of PM-containing Archaea encode homologs of the bacterial genes involved in PG biosynthesis, even though neither their specific functions nor the relationships within the corresponding inter-domain phylogenies have been investigated so far. In this work, we devised a pangenomic bioinformatic pipeline to identify proteins for PM biosynthesis in Archaea without prior genetic knowledge. The taxonomic distribution and evolutionary relationships of the candidate proteins were studied in detail in Archaea and Bacteria through HMM sequence mining and phylogenetic inference of the Mur domain-containing family, the ATP-grasp superfamily, and the MraY-like family. Our results show that archaeal muramyl ligases are of bacterial origin but diversified through a mixture of horizontal gene transfers and gene duplications. However, in the ATP-grasp and MraY-like families, the archaeal members were not found to originate from Bacteria. Our pangenomic approach further identified five new genes potentially involved in PM synthesis and that would deserve functional characterization.IMPORTANCEMethanobrevibacter smithii is an archaea commonly found in the human gut, but its presence alongside pathogenic bacteria during infections has led some researchers to consider it as an opportunistic pathogen. Fortunately, endoisopeptidases isolated from phages, such as PeiW and PeiP, can cleave the cell walls of M. smithii and other pseudomurein-containing archaea. However, additional research is required to identify effective anti-archaeal agents to combat these opportunistic microorganisms. A better understanding of the pseudomurein cell wall and its biosynthesis is necessary to achieve this goal. Our study sheds light on the origin of cell wall structures in those microorganisms, showing that the archaeal muramyl ligases responsible for its formation have bacterial origins. This discovery challenges the conventional view of the cell-wall architecture in the last archaeal common ancestor and shows that the distinction between "common origin" and "convergent evolution" can be blurred in some cases.

LogoMotif: A Comprehensive Database of Transcription Factor Binding Site Profiles in Actinobacteria

Actinobacteria undergo a complex multicellular life cycle and produce a wide range of specialized metabolites, including the majority of the antibiotics. These biological processes are controlled by intricate regulatory pathways, and to better understand how they are controlled we need to augment our insights into the transcription factor binding sites. Here, we present LogoMotif (https://logomotif.bioinformatics.nl), an open-source database for characterized and predicted transcription factor binding sites in Actinobacteria, along with their cognate position weight matrices and hidden Markov models. Genome-wide predictions of binding site locations in Streptomyces model organisms are supplied and visualized in interactive regulatory networks. In the web interface, users can freely access, download and investigate the underlying data. With this curated collection of actinobacterial regulatory interactions, LogoMotif serves as a basis for binding site predictions, thus providing users with clues on how to elicit the expression of genes of interest and guide genome mining efforts.

Genome-wide identification of SHMT family genes in alfalfa (Medicago sativa) and its functional analyses under various abiotic stresses

BACKGROUND

Alfalfa (Medicago sativa L.) is the most widely planted legume forage and one of the most economically valuable crops in the world. Serine hydroxymethyltransferase (SHMT), a pyridoxal phosphate-dependent enzyme, plays crucial roles in plant growth, development, and stress responses. To date, there has been no comprehensive bioinformatics investigation conducted on the SHMT genes in M. sativa.

RESULTS

Here, we systematically analyzed the phylogenetic relationship, expansion pattern, gene structure, cis-acting elements, and expression profile of the MsSHMT family genes. The result showed that a total of 15 SHMT members were identified from the M. sativa genome database. Phylogenetic analysis demonstrated that the MsSHMTs can be divided into 4 subgroups and conserved with other plant homologues. Gene structure analysis found that the exons of MsSHMTs ranges from 3 to 15. Analysis of cis-acting elements found that each of the MsSHMT genes contained different kinds of hormones and stress-related cis-acting elements in their promoter regions. Expression and function analysis revealed that MsSHMTs expressed in all plant tissues. qRT-PCR analysis showed that MsSHMTs induced by ABA, Salt, and drought stresses.

CONCLUSIONS

These results provided definite evidence that MsSHMTs might involve in growth, development and adversity responses in M. sativa, which laid a foundation for future functional studies of MsSHMTs.

An overview of the two-component system GarR/GarS role on antibiotic production in Streptomyces coelicolor

The Streptomyces genus comprises Gram-positive bacteria known to produce over two-thirds of the antibiotics used in medical practice. The biosynthesis of these secondary metabolites is highly regulated and influenced by a range of nutrients present in the growth medium. In Streptomyces coelicolor, glucose inhibits the production of actinorhodin (ACT) and undecylprodigiosin (RED) by a process known as carbon catabolite repression (CCR). However, the mechanism mediated by this carbon source still needs to be understood. It has been observed that glucose alters the transcriptomic profile of this actinobacteria, modifying different transcriptional regulators, including some of the one- and two-component systems (TCSs). Under glucose repression, the expression of one of these TCSs SCO6162/SCO6163 was negatively affected. We aimed to study the role of this TCS on secondary metabolite formation to define its influence in this general regulatory process and likely establish its relationship with other transcriptional regulators affecting antibiotic biosynthesis in the Streptomyces genus. In this work, in silico predictions suggested that this TCS can regulate the production of the secondary metabolites ACT and RED by transcriptional regulation and protein-protein interactions of the transcriptional factors (TFs) with other TCSs. These predictions were supported by experimental procedures such as deletion and complementation of the TFs and qPCR experiments. Our results suggest that in the presence of glucose, the TCS SCO6162/SCO6163, named GarR/GarS, is an important negative regulator of the ACT and RED production in S. coelicolor. KEY POINTS: • GarR/GarS is a TCS with domains for signal transduction and response regulation • GarR/GarS is an essential negative regulator of the ACT and RED production • GarR/GarS putatively interacts with and regulates activators of ACT and RED.

Harnessing regulatory networks in Actinobacteria for natural product discovery

Microbes typically live in complex habitats where they need to rapidly adapt to continuously changing growth conditions. To do so, they produce an astonishing array of natural products with diverse structures and functions. Actinobacteria stand out for their prolific production of bioactive molecules, including antibiotics, anticancer agents, antifungals, and immunosuppressants. Attention has been directed especially towards the identification of the compounds they produce and the mining of the large diversity of biosynthetic gene clusters (BGCs) in their genomes. However, the current return on investment in random screening for bioactive compounds is low, while it is hard to predict which of the millions of BGCs should be prioritized. Moreover, many of the BGCs for yet undiscovered natural products are silent or cryptic under laboratory growth conditions. To identify ways to prioritize and activate these BGCs, knowledge regarding the way their expression is controlled is crucial. Intricate regulatory networks control global gene expression in Actinobacteria, governed by a staggering number of up to 1000 transcription factors per strain. This review highlights recent advances in experimental and computational methods for characterizing and predicting transcription factor binding sites and their applications to guide natural product discovery. We propose that regulation-guided genome mining approaches will open new avenues toward eliciting the expression of BGCs, as well as prioritizing subsets of BGCs for expression using synthetic biology approaches.

ONE-SENTENCE SUMMARY

This review provides insights into advances in experimental and computational methods aimed at predicting transcription factor binding sites and their applications to guide natural product discovery.

Versatility and Complexity: Common and Uncommon Facets of LysR-Type Transcriptional Regulators

LysR-type transcriptional regulators (LTTRs) form one of the largest families of bacterial regulators. They are widely distributed and contribute to all aspects of metabolism and physiology. Most are homotetramers, with each subunit composed of an N-terminal DNA-binding domain followed by a long helix connecting to an effector-binding domain. LTTRs typically bind DNA in the presence or absence of a small-molecule ligand (effector). In response to cellular signals, conformational changes alter DNA interactions, contact with RNA polymerase, and sometimes contact with other proteins. Many are dual-function repressor-activators, although different modes of regulation may occur at multiple promoters. This review presents an update on the molecular basis of regulation, the complexity of regulatory schemes, and applications in biotechnology and medicine. The abundance of LTTRs reflects their versatility and importance. While a single regulatory model cannot describe all family members, a comparison of similarities and differences provides a framework for future study.