The formation and evolution of the Earth’s inner core
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MADS31 supports female germline development by repressing the post-fertilization programme in cereal ovules
The female germline of flowering plants develops within a niche of sporophytic (somatic) ovule cells, also referred to as the nucellus. How niche cells maintain their own somatic developmental programme, yet support the development of adjoining germline cells, remains largely unknown. Here we report that MADS31, a conserved MADS-box transcription factor from the B-sister subclass, is a potent regulator of niche cell identity. In barley, MADS31 is preferentially expressed in nucellar cells directly adjoining the germline, and loss-of-function mads31 mutants exhibit deformed and disorganized nucellar cells, leading to impaired germline development and partial female sterility. Remarkably similar phenotypes are observed in mads31 mutants in wheat, suggesting functional conservation within the Triticeae tribe. Molecular assays indicate that MADS31 encodes a potent transcriptional repressor, targeting genes in the ovule that are normally active in the seed. One prominent target of MADS31 is NRPD4b, a seed-expressed component of RNA polymerase IV/V that is involved in epigenetic regulation. NRPD4b is directly repressed by MADS31 in vivo and is derepressed in mads31 ovules, while overexpression of NRPD4b recapitulates the mads31 ovule phenotype. Thus, repression of NRPD4b by MADS31 is required to maintain ovule niche functionality. Our findings reveal a new mechanism by which somatic ovule tissues maintain their identity and support germline development before transitioning to the post-fertilization programme.
Mendelian non-syndromic and syndromic hearing loss genes contribute to presbycusis
Age-related (AR) hearing loss (HL) is the most prevalent sensorineural disorder in older adults. Here we demonstrate that rare-variants in well-established Mendelian HL genes play an important role in ARHL etiology. In all we identified 32 Mendelian HL genes which are associated with ARHL. We performed single and rare-variant aggregate association analyses using exome data obtained from white-Europeans with self-reported hearing phenotypes from the UK Biobank. Our analysis revealed previously unreported associations between ARHL and rare-variants in Mendelian non-syndromic and syndromic HL genes, including MYO15A, and WFS1. Additionally, rare-variant aggregate association analyses identified associations with Mendelian HL genes i.e., ACTG1, GRHL2, KCNQ4, MYO7A, PLS1, TMPRSS3, and TNRC6B. Four novel ARHL genes were also detected: FBXO2 and PALM3, implicated in HL in mice, TWF1, associated with HL in Dalmatian dogs, and TXNDC17. In-silico analyses provided further evidence of inner ear expression of these genes in both murine and human models, supporting their relevance to ARHL. Analysis of variants with minor allele frequency >0.005 revealed additional ARHL associations with known e.g., ILDR1 and novel i.e., ABHD12, COA8, KANSL1, SERAC1, and UBE3B Mendelian non-syndromic and syndromic HL genes as well as ARHL associations with genes that have not been previously reported to be involved in HL e.g., VCL. Rare-variants in Mendelian HL genes typically exhibited higher effect sizes for ARHL compared to those in other associated genes. In conclusion, this study highlights the critical role Mendelian non-syndromic and syndromic HL genes play in the etiology of ARHL.
Co-option and neofunctionalization of stomatal executors for defence against herbivores in Brassicales
Co-option of gene regulatory networks leads to the acquisition of new cell types and tissues. Stomata, valves formed by guard cells (GCs), are present in most land plants and regulate CO2 exchange. The transcription factor (TF) FAMA globally regulates GC differentiation. In the Brassicales, FAMA also promotes the development of idioblast myrosin cells (MCs), another type of specialized cell along the vasculature essential for Brassicales-specific chemical defences. Here we show that in Arabidopsis thaliana, FAMA directly induces the TF gene WASABI MAKER (WSB), which triggers MC differentiation. WSB and STOMATAL CARPENTER 1 (SCAP1, a stomatal lineage-specific direct FAMA target), synergistically promote GC differentiation. wsb mutants lacked MCs and the wsb scap1 double mutant lacked normal GCs. Evolutionary analyses revealed that WSB is conserved across stomatous angiosperms. We propose that the conserved and reduced transcriptional FAMA–WSB module was co-opted before evolving to induce MC differentiation.
Archaean green-light environments drove the evolution of cyanobacteria’s light-harvesting system
Cyanobacteria induced the great oxidation event around 2.4 billion years ago, probably triggering the rise in aerobic biodiversity. While chlorophylls are universal pigments used by all phototrophic organisms, cyanobacteria use additional pigments called phycobilins for their light-harvesting antennas—phycobilisomes—to absorb light energy at complementary wavelengths to chlorophylls. Nonetheless, an enigma persists: why did cyanobacteria need phycobilisomes? Here, we demonstrate through numerical simulations that the underwater light spectrum during the Archaean era was probably predominantly green owing to oxidized Fe(III) precipitation. The green-light environments, probably shaped by photosynthetic organisms, may have directed their own photosynthetic evolution. Genetic engineering of extant cyanobacteria, simulating past natural selection, suggests that cyanobacteria that acquired a green-specialized phycobilin called phycoerythrobilin could have flourished under green-light environments. Phylogenetic analyses indicate that the common ancestor of modern cyanobacteria embraced all key components of phycobilisomes to establish an intricate energy transfer mechanism towards chlorophylls using green light and thus gained strong selective advantage under green-light conditions. Our findings highlight the co-evolutionary relationship between oxygenic phototrophs and light environments that defined the aquatic landscape of the Archaean Earth and envision the green colour as a sign of the distinct evolutionary stage of inhabited planets.
Macroevolution along developmental lines of least resistance in fly wings
Evolutionary change requires genetic variation, and a reigning paradigm in biology is that rates of microevolution can be predicted from estimates of available genetic variation within populations. However, the accuracy of such predictions should decay on longer evolutionary timescales, as the influence of genetic constraints diminishes. Here we show that intrinsic developmental variability and standing genetic variation in wing shape in two distantly related flies, Drosophila melanogaster and Sepsis punctum, are aligned and predict deep divergence in the dipteran phylogeny, spanning >900 taxa and 185 million years. This alignment cannot be easily explained by constraint hypotheses unless most of the quantified standing genetic variation is associated with deleterious side effects and is effectively unusable for evolution. However, phenotyping of 71 genetic lines of S. punctum revealed no covariation between wing shape and fitness, lending no support to this hypothesis. We also find little evidence for genetic constraints on the pace of wing shape evolution along the dipteran phylogeny. Instead, correlational selection related to allometric scaling, simultaneously shaping developmental variability and deep divergence in fly wings, emerges as a potential explanation for the observed alignment. This suggests that pervasive natural selection has the potential to shape developmental architectures of some morphological characters such that their intrinsic variability predicts their long-term evolution.
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