HP6/Umbrea is dispensable for viability and fertility, suggesting essentiality of newly evolved genes is rare.

The newly evolved gene Heterochromatin Protein 6 (HP6), which has been previously classified as essential, challenged the dogma that functions required for viability are only seen in genes with a long evolutionary history. Based on previous RNA-sequencing analysis in Drosophila germ cells, we asked whether HP6 might play a role in germline development. Surprisingly, we found that CRISPR-generated HP6 mutants are viable and fertile. Using previously generated mutants, we identified an independent lethal allele and an RNAi off-target effect that prevented accurate interpretation of HP6 essentiality. By reviewing existing data, we found that the vast majority of young genes that were previously classified as essential were indeed viable when tested with orthologous methods. Together, our data call into question the frequency with which newly evolved genes gain essential functions and suggest that using multiple independent genetic methods is essential when probing the functions of young genes.

Review: WRKY transcription factors: Understanding the functional divergence.

WRKY transcription factors (TFs) play crucial roles in the growth and development of plants and their response to environmental changes. WRKY TFs have been detected in sequenced plant genomes. The functions and regulatory networks of many WRKY TFs, especially from Arabidopsis thaliana (AtWRKY TFs), have been revealed, and the origin of WRKY TFs in plants is clear. Nonetheless, the relationship between WRKY TFs function and classification is unclear. Furthermore, the functional divergence of homologous WRKY TFs in plants is unclear. In this review, WRKY TFs were explored based on WRKY-related literature published from 1994 to 2022. WRKY TFs were identified in 234 species at the genome and transcriptome levels. The biological functions of ∼ 71 % of AtWRKY TFs were uncovered. Although functional divergence occurred in homologous WRKY TFs, different WRKY TF groups had no preferential function.

Understanding the proteome encoded by "non-coding RNAs": new insights into human genome.

A great number of non-coding RNAs (ncRNAs) account for the majority of the genome. The translation of these ncRNAs has been noted but seriously underestimated due to both technological and theoretical limitations. Based on the development of ribosome profiling (Ribo-seq), full length translating RNA analysis (RNC-seq) and mass spectrometry technology, more and more ncRNAs are being found to be translated in different organism, and some of them can produce functional peptides. While recently, not only individual new functional proteins, but also a new proteome have been experimentally discovered to be encoded by endogenous lncRNAs and circRNAs. These new proteins are of biological significance, suggesting the connection of the translation of ncRNAs to human physiology and diseases. Therefore, an in-depth and systematic understanding of the coding capabilities of ncRNAs is necessary for basic biology and medicine. In this review, we summarize the advances in the field of discovering this new proteome, i.e. "ncRNA-coded" proteins.

Evolutionary balance between LRR domain loss and young NBS-LRR genes production governs disease resistance in Arachis hypogaea cv. Tifrunner.

BACKGROUND: Cultivated peanut (Arachis hypogaea L.) is an important oil and protein crop, but it has low disease resistance; therefore, it is important to reveal the number, sequence features, function, and evolution of genes that confer resistance. Nucleotide-binding site-leucine-rich repeats (NBS-LRRs) are resistance genes that are involved in response to various pathogens. RESULTS: We identified 713 full-length NBS-LRRs in A. hypogaea cv. Tifrunner. Genetic exchange events occurred on NBS-LRRs in A. hypogaea cv. Tifrunner, which were detected in the same subgenomes and also found in different subgenomes. Relaxed selection acted on NBS-LRR proteins and LRR domains in A. hypogaea cv. Tifrunner. Using quantitative trait loci (QTL), we found that NBS-LRRs were involved in response to late leaf spot, tomato spotted wilt virus, and bacterial wilt in A. duranensis (2 NBS-LRRs), A. ipaensis (39 NBS-LRRs), and A. hypogaea cv. Tifrunner (113 NBS-LRRs). In A. hypogaea cv. Tifrunner, 113 NBS-LRRs were classified as 75 young and 38 old NBS-LRRs, indicating that young NBS-LRRs were involved in response to disease after tetraploidization. However, compared to A. duranensis and A. ipaensis, fewer LRR domains were found in A. hypogaea cv. Tifrunner NBS-LRR proteins, partly explaining the lower disease resistance of the cultivated peanut. CONCLUSIONS: Although relaxed selection acted on NBS-LRR proteins and LRR domains, LRR domains were preferentially lost in A. hypogaea cv. Tifrunner compared to A. duranensis and A. ipaensis. The QTL results suggested that young NBS-LRRs were important for resistance against diseases in A. hypogaea cv. Tifrunner. Our results provid insight into the greater susceptibility of A. hypogaea cv. Tifrunner to disease compared to A. duranensis and A. ipaensis.

The characteristic of Arachis duranensis-specific genes and their potential function.

Arachis species produce flowers aerially, and then grow into the ground, where they develop into fruits; a feature that is unique to Arachis species. We hypothesized that Arachis species evolved genes specifically involved in the control of aerial flowers and the formation of underground fruits. Arachis duranensis is more resistant to biotic and abiotic stressors. Here, we compared different legume species and identified Arachis duranensis-specific genes. We analyzed gene expression patterns, base substitution patterns and sequence features between genes that are conserved across legume plants and A. duranensis-specific genes. Furthermore, we tested the role of A. duranensis-specific genes during seed development, response to nematode Meloidogyne arenaria infection and drought stress. We found that A. duranensis-specific genes had characteristics of young genes. The gene expression level and breadth were lower in the A. duranensis-specific genes compared to conserved genes. The A. duranensis-specific genes had higher codon usage bias than conserved genes, and the polypeptide length and GC content at the three codon sites were lower compared to conserved genes. Of the A. duranensis-specific genes, single-copy and duplicated genes had different features. The RNA-seq result showed A. duranensis-specific genes were involved in seed development, as well as response to nematode infection and drought stress. In addition, we detected asymmetric functions in A. duranensis-specific duplicated genes in response to nematode infection and drought stress.

Genomic Complexity Places Less Restrictions on the Evolution of Young Coexpression Networks than Protein-Protein Interactions.

The differences in evolutionary patterns of young protein-protein interactions (PPIs) among distinct species have long been a puzzle. However, based on our genome-wide analysis of available integrated experimental data, we confirm that young genes preferentially integrate into ancestral PPI networks, and that this manner is consistent in all of six model organisms with widely different levels of phenotypic complexity. We demonstrate that the level of restrictions placed on the evolution of biological networks declines with a decrease of phenotypic complexity. Compared with young PPI networks, new co-expression links have less evolutionary restrictions, so a young gene with a high possibility to be coexpressed other young genes relatively frequently emerges in the four simpler genomes among the six studied. However, it is not favorable for such young-young coexpression in terms of a young gene evolving into a coexpression hub, so the coexpression pattern could gradually decline. To explain this apparent contradiction, we suggest that young genes that are initially peripheral to networks are temporarily coexpressed with other young genes, driving functional evolution because of low selective pressure. However, as the expression levels of genes increase and they gradually develop a greater effect on fitness, young genes start to be coexpressed more with members of ancestral networks and less with other young genes. Our findings provide new insights into the evolution of biological networks.

Integrative analyses of RNA editing, alternative splicing, and expression of young genes in human brain transcriptome by deep RNA sequencing.

Next-generation RNA sequencing has been successfully used for identification of transcript assembly, evaluation of gene expression levels, and detection of post-transcriptional modifications. Despite these large-scale studies, additional comprehensive RNA-seq data from different subregions of the human brain are required to fully evaluate the evolutionary patterns experienced by the human brain transcriptome. Here, we provide a total of 6.5 billion RNA-seq reads from different subregions of the human brain. A significant correlation was observed between the levels of alternative splicing and RNA editing, which might be explained by a competition between the molecular machineries responsible for the splicing and editing of RNA. Young human protein-coding genes demonstrate biased expression to the neocortical and non-neocortical regions during evolution on the lineage leading to humans. We also found that a significantly greater number of young human protein-coding genes are expressed in the putamen, a tissue that was also observed to have the highest level of RNA-editing activity. The putamen, which previously received little attention, plays an important role in cognitive ability, and our data suggest a potential contribution of the putamen to human evolution.

Expression profile and gene age jointly shaped the genome-wide distribution of premature termination codons in a Drosophila melanogaster population.

Widespread premature termination codon mutations (PTCs) were recently observed in human and fly populations. We took advantage of the population resequencing data in the Drosophila Genetic Reference Panel to investigate how the expression profile and the evolutionary age of genes shaped the allele frequency distribution of PTCs. After generating a high-quality data set of PTCs, we clustered genes harboring PTCs into three categories: genes encoding low-frequency PTCs (≤ 1.5%), moderate-frequency PTCs (1.5-10%), and high-frequency PTCs (>10%). All three groups show narrow transcription compared with PTC-free genes, with the moderate- and high-PTC frequency groups showing a pronounced pattern. Moreover, nearly half (42%) of the PTC-encoding genes are not expressed in any tissue. Interestingly, the moderate-frequency PTC group is strongly enriched for genes expressed in midgut, whereas genes harboring high-frequency PTCs tend to have sex-specific expression. We further find that although young genes born in the last 60 My compose a mere 9% of the genome, they represent 16%, 30%, and 50% of the genes containing low-, moderate-, and high-frequency PTCs, respectively. Among DNA-based and RNA-based duplicated genes, the child copy is approximately twice as likely to contain PTCs as the parent copy, whereas young de novo genes are as likely to encode PTCs as DNA-based duplicated new genes. Based on these results, we conclude that expression profile and gene age jointly shaped the landscape of PTC-mediated gene loss. Therefore, we propose that new genes may need a long time to become stably maintained after the origination.

"Out of pollen" hypothesis for origin of new genes in flowering plants: study from Arabidopsis thaliana.

New genes, which provide material for evolutionary innovation, have been extensively studied for many years in animals where it is observed that they commonly show an expression bias for the testis. Thus, the testis is a major source for the generation of new genes in animals. The source tissue for new genes in plants is unclear. Here, we find that new genes in plants show a bias in expression to mature pollen, and are also enriched in a gene coexpression module that correlates with mature pollen in Arabidopsis thaliana. Transposable elements are significantly enriched in the new genes, and the high activity of transposable elements in the vegetative nucleus, compared with the germ cells, suggests that new genes are most easily generated in the vegetative nucleus in the mature pollen. We propose an "out of pollen" hypothesis for the origin of new genes in flowering plants.