Recurrent sequence evolution after independent gene duplication

Single-cell Transcriptomic Studies Unveil Potential Nodes of the Notochord Gene Regulatory Network

Transcription factors (TFs) are DNA-binding proteins able to modulate the timing, location, and levels of gene expression by binding to regulatory DNA regions. Therefore, the repertoire of TFs present in the genome of a multicellular organism and the expression of variable constellations of TFs in different cellular cohorts determine the distinctive characteristics of developing tissues and organs. The information on tissue-specific assortments of TFs, their cross-regulatory interactions, and the genes/regulatory regions targeted by each TF is summarized in gene regulatory networks (GRNs), which provide genetic blueprints for the specification, development, and differentiation of multicellular structures. In this study, we review recent transcriptomic studies focused on the complement of TFs expressed in the notochord, a distinctive feature of all chordates. We analyzed notochord-specific datasets available from organisms representative of the three chordate subphyla, and highlighted lineage-specific variations in the suite of TFs expressed in their notochord. We framed the resulting findings within a provisional evolutionary scenario, which allows the formulation of hypotheses on the genetic/genomic changes that sculpted the structure and function of the notochord on an evolutionary scale.

Genetic Channelization Mechanism of Four Chalcone Isomerase Homologous Genes for Synergistic Resistance to Fusarium wilt in Gossypium barbadense L

Duplication events occur very frequently during plant evolution. The genes in the duplicated pathway or network can evolve new functions through neofunctionalization and subfunctionalization. Flavonoids are secondary metabolites involved in plant development and defense. Our previous transcriptomic analysis of F6 recombinant inbred lines (RILs) and the parent lines after Fusarium oxysporum f. sp. vasinfectum (Fov) infection showed that CHI genes have important functions in cotton. However, there are few reports on the possible neofunctionalization differences of CHI family paralogous genes involved in Fusarium wilt resistance in cotton. In this study, the resistance to Fusarium wilt, expression of metabolic pathway-related genes, metabolite content, endogenous hormone content, reactive oxygen species (ROS) content and subcellular localization of four paralogous CHI family genes in cotton were investigated. The results show that the four paralogous CHI family genes may play a synergistic role in Fusarium wilt resistance. These results revealed a genetic channelization mechanism that can regulate the metabolic flux homeostasis of flavonoids under the mediation of endogenous salicylic acid (SA) and methyl jasmonate (MeJA) via the four paralogous CHI genes, thereby achieving disease resistance. Our study provides a theoretical basis for studying the evolutionary patterns of homologous plant genes and using homologous genes for molecular breeding.

Kinase regulators evolved into two families by gain and loss of ability to bind plant steroid receptors

All biological functions evolve by fixing beneficial mutations and removing deleterious ones. Therefore, continuously fixing and removing the same essential function to separately diverge monophyletic gene families sounds improbable. Yet, here we report that brassinosteroid insensitive1 kinase inhibitor1 (BKI1)/membrane-associated kinase regulators (MAKRs) regulating a diverse function evolved into BKI1 and MAKR families from a common ancestor by respectively enhancing and losing ability to bind brassinosteroid receptor brassinosteroid insensitive1 (BRI1). The BKI1 family includes BKI1, MAKR1/BKI1-like (BKL) 1, and BKL2, while the MAKR family contains MAKR2-6. Seedless plants contain only BKL2. In seed plants, MAKR1/BKL1 and MAKR3, duplicates of BKL2, gained and lost the ability to bind BRI1, respectively. In angiosperms, BKL2 lost the ability to bind BRI1 to generate MAKR2, while BKI1 and MAKR6 were duplicates of MAKR1/BKL1 and MAKR3, respectively. In dicots, MAKR4 and MAKR5 were duplicates of MAKR3 and MAKR2, respectively. Importantly, BKI1 localized in the plasma membrane, but BKL2 localized to the nuclei while MAKR1/BKL1 localized throughout the whole cell. Importantly, BKI1 strongly and MAKR1/BKL1 weakly inhibited plant growth, but BKL2 and the MAKR family did not inhibit plant growth. Functional study of the chimeras of their N- and C-termini showed that only the BKI1 family was partially reconstructable, supporting stepwise evolution by a seesaw mechanism between their C- and N-termini to alternately gain an ability to bind and inhibit BRI1, respectively. Nevertheless, the C-terminal BRI1-interacting motif best defines the divergence of BKI1/MAKRs. Therefore, BKI1 and MAKR families evolved by gradually gaining and losing the same function, respectively, extremizing divergent evolution and adding insights into gene (BKI1/MAKR) duplication and divergence.

Integrating Phylogenetics With Intron Positions Illuminates the Origin of the Complex Spliceosome

Eukaryotic genes are characterized by the presence of introns that are removed from pre-mRNA by a spliceosome. This ribonucleoprotein complex is comprised of multiple RNA molecules and over a hundred proteins, which makes it one of the most complex molecular machines that originated during the prokaryote-to-eukaryote transition. Previous works have established that these introns and the spliceosomal core originated from self-splicing introns in prokaryotes. Yet, how the spliceosomal core expanded by recruiting many additional proteins remains largely elusive. In this study, we use phylogenetic analyses to infer the evolutionary history of 145 proteins that we could trace back to the spliceosome in the last eukaryotic common ancestor. We found that an overabundance of proteins derived from ribosome-related processes was added to the prokaryote-derived core. Extensive duplications of these proteins substantially increased the complexity of the emerging spliceosome. By comparing the intron positions between spliceosomal paralogs, we infer that most spliceosomal complexity postdates the spread of introns through the proto-eukaryotic genome. The reconstruction of early spliceosomal evolution provides insight into the driving forces behind the emergence of complexes with many proteins during eukaryogenesis.

Dynamic Long-Range Interactions Influence Substrate Binding and Catalysis by Human Histidine Triad Nucleotide-Binding Proteins (HINTs), Key Regulators of Multiple Cellular Processes and Activators of Antiviral ProTides

Human histidine triad nucleotide-binding (hHINT) proteins catalyze nucleotide phosphoramidase and acyl-phosphatase reactions that are essential for the activation of antiviral proTides, such as Sofosbuvir and Remdesivir. hHINT1 and hHINT2 are highly homologous but exhibit disparate roles as regulators of opioid tolerance (hHINT1) and mitochondrial activity (hHINT2). NMR studies of hHINT1 reveal a pair of dynamic surface residues (Q62, E100), which gate a conserved water channel leading to the active site 13 Å away. hHINT2 crystal structures identify analogous residues (R99, D137) and water channel. hHINT1 Q62 variants significantly alter the steady-state k_cat and K_m for turnover of the fluorescent substrate (TpAd), while stopped-flow kinetics indicate that K_D also changes. hHINT2, like hHINT1, exhibits a burst phase of adenylation, monitored by fluorescent tryptamine release, prior to rate-limiting hydrolysis and nucleotide release. hHINT2 exhibits a much smaller burst-phase amplitude than hHINT1, which is further diminished in hHINT2 R99Q. Kinetic simulations suggest that amplitude variations can be accounted for by a variable fluorescent yield of the E·S complex from changes in the environment of bound TpAd. Isothermal titration calorimetry measurements of inhibitor binding show that these hHINT variants also alter the thermodynamic binding profile. We propose that these altered surface residues engender long-range dynamic changes that affect the orientation of bound ligands, altering the thermodynamic and kinetic characteristics of hHINT active site function. Thus, studies of the cellular roles and proTide activation potential by hHINTs should consider the importance of long-range interactions and possible protein binding surfaces far from the active site.

Paleoproteomics

Paleoproteomics, the study of ancient proteins, is a rapidly growing field at the intersection of molecular biology, paleontology, archaeology, paleoecology, and history. Paleoproteomics research leverages the longevity and diversity of proteins to explore fundamental questions about the past. While its origins predate the characterization of DNA, it was only with the advent of soft ionization mass spectrometry that the study of ancient proteins became truly feasible. Technological gains over the past 20 years have allowed increasing opportunities to better understand preservation, degradation, and recovery of the rich bioarchive of ancient proteins found in the archaeological and paleontological records. Growing from a handful of studies in the 1990s on individual highly abundant ancient proteins, paleoproteomics today is an expanding field with diverse applications ranging from the taxonomic identification of highly fragmented bones and shells and the phylogenetic resolution of extinct species to the exploration of past cuisines from dental calculus and pottery food crusts and the characterization of past diseases. More broadly, these studies have opened new doors in understanding past human-animal interactions, the reconstruction of past environments and environmental changes, the expansion of the hominin fossil record through large scale screening of nondiagnostic bone fragments, and the phylogenetic resolution of the vertebrate fossil record. Even with these advances, much of the ancient proteomic record still remains unexplored. Here we provide an overview of the history of the field, a summary of the major methods and applications currently in use, and a critical evaluation of current challenges. We conclude by looking to the future, for which innovative solutions and emerging technology will play an important role in enabling us to access the still unexplored "dark" proteome, allowing for a fuller understanding of the role ancient proteins can play in the interpretation of the past.

Inter-paralog amino acid inversion events in large phylogenies of duplicated proteins

Connecting protein sequence to function is becoming increasingly relevant since high-throughput sequencing studies accumulate large amounts of genomic data. In order to go beyond the existing database annotation, it is fundamental to understand the mechanisms underlying functional inheritance and divergence. If the homology relationship between proteins is known, can we determine whether the function diverged? In this work, we analyze different possibilities of protein sequence evolution after gene duplication and identify “inter-paralog inversions”, i.e., sites where the relationship between the ancestry and the functional signal is decoupled. The amino acids in these sites are masked from being recognized by other prediction tools. Still, they play a role in functional divergence and could indicate a shift in protein function. We develop a method to specifically recognize inter-paralog amino acid inversions in a phylogeny and test it on real and simulated datasets. In a dataset built from the Epidermal Growth Factor Receptor (EGFR) sequences found in 88 fish species, we identify 19 amino acid sites that went through inversion after gene duplication, mostly located at the ligand-binding extracellular domain. Our work uncovers an outcome of protein duplications with direct implications in protein functional annotation and sequence evolution. The developed method is optimized to work with large protein datasets and can be readily included in a targeted protein analysis pipeline.

Proteins are critical components of living systems because they facilitate most biological processes like protein synthesis, DNA replication, chemical catalysis, etc. Proteins are encoded in their genes. During evolution, genes accumulate mutations that get translated at the protein level. These mutations can be “neutral” if they do not affect the protein function immediately and directly; otherwise, mutations can be functional if they directly modify protein function. An event that provides an opportunity to study protein function is gene duplication namely, when two copies of a gene encoding the same protein appear. One copy of the protein often retains the same function while the other is free to diverge and specialize to a different function. This work sheds light on an alternative outcome of gene duplication that might be critical to discern between neutral and functional mutations. By looking at 88 fish genomes, we found proteins in which the evolution of their sequences does not follow the expected pattern of divergence after gene duplication. In this case, the protein sequence of a subgroup of species diverges in the copy expected to retain its function, while the sequence is retained in the expectedly divergent one. We called this event “inter-paralog amino acid inversion”. Our data shows that this “inversion” event is correlated to function, and its detection has to be considered for assigning protein functions correctly.

Evolutionary History of RNA Modifications at N6-Adenosine Originating from the R-M System in Eukaryotes and Prokaryotes

Simple Summary

The m⁶A is the most abundant and well-studied modification of mRNA, and plays an important role in transcription and translation. It is known to be evolutionarily conserved machinery present in the last eukaryotic common ancestor (LECA). The writers and erasers responsible for adding or removing m⁶A belong to specific protein families, respectively, suggesting that these members are evolutionarily related. However, only some of these mRNA m⁶A modification-associated proteins have been studied from an evolutionary perspective, while there has been no comprehensive and systematic analysis of the distributions and evolutionary history of N6mA-associated proteins in the three kingdoms of life. In this study, we identified orthologues of all the reported N6mA-associated proteins in 88 organisms from three kingdoms of life and comprehensively reconstructed the evolutionary history of the RNA N6mA modification machinery. The results demonstrate that RNA N6mA-MTases are derived from at least two different types of prokaryotic DNA MTases (class α and β MTases). As the m⁶A reader, YTH proteins may be acquired by LECA from an individual prokaryotic YTH-domain protein that evolved from the N-terminals of an R-M system endonuclease. In addition, the origin of eukaryotic ALKBH family proteins is inferred to be driven by at least two occasions of independent HTG from the bacterial ALKB family.

Abstract

Methylation at the N6-position of adenosine (N6mA) on mRNA (m⁶A) is one of the most widespread, highly selective and dynamically regulated RNA modifications and plays an important role in transcription and translation. In the present study, a comprehensive analysis of phylogenetic relationships, conserved domain sequence characteristics and protein structure comparisons were employed to explore the distribution of RNA N6mA modification (m⁶A, m^6,6A, m⁶Am, m^{6, 6}Am and m⁶t⁶A)-associated proteins (writers, readers and erasers) in three kingdoms of life and reveal the evolutionary history of these modifications. These findings further confirmed that the restriction-modification (R-M) system is the origin of DNA and RNA N6mA modifications. Among them, the existing mRNA m⁶A modification system derived from the last eukaryotic common ancestor (LECA) is the evolutionary product of elements from the last universal common ancestor (LUCA) or driven by horizontal gene transfer (HGT) from bacterial elements. The subsequent massive gene gains and losses contribute to the development of unique and diverse functions in distinct species. Particularly, RNA methyltransferases (MTases) as the writer responsible for adding N6mA marks on mRNA and ncRNAs may have evolved from class α and β prokaryotic “orphan” MTases originating from the R-M system. The reader, YTH proteins that specifically recognize the m⁶A deposit, may be acquired by LECA from an individual prokaryotic YTH-domain protein that evolved from N-terminals of an R-M system endonuclease. The eraser, which emerged from the ALKB family (ALKBH5 and FTO) in eukaryotes, may be driven by independent HTG from bacterial ALKB proteins. The evolutionary history of RNA N6mA modifications was inferred in the present study, which will deepen our understanding of these modifications in different species.