Biology subjects

Raval, P. K.

Publications and source records attributed to Raval, P. K..

12 recordsLinked to original sources

bioRxiv2026

Rapid plastid isolation reveals the chloroplast proteome and structures of the chlororibosome large subunit and RuBisCO in Marchantia polymorpha

Plastids house the biology of eukaryotic photosynthesis. While 1000s of plastid genomes have been sequenced, the availability of less than ten proteomes and only two species with full 70S plastid ribosomal structures limit our understanding of plant evolution. We optimized a protocol for the rapid isolation of Marchantia polymorpha plastids that provides a highly enriched and intact organelle fraction from gradient volumes as little as 2 mL. The approach was successfully applied to six other species. Focusing on M. polymorpha, we determined the proteome of the plastid fraction, identifying 1337 nuclear-encoded proteins with a high confidence, where 83% belong to orthologs shared with angiosperms. We further isolated protein complexes by RNA affinity purification using poly-lysine and provide the high-resolution structures of the 50S subunit of the chloroplast ribosome and RuBisCO using cryogenic EM and image reconstruction to 2.23 and 2.12 [A] resolution, respectively. For plastids, our data show that the genome reduction event experienced by the bryophyte common ancestor has had little impact on the organelles complexity and they underscore a high level of structural conservation of key components. Our data provide novel resources to explore the functional evolution of plastid proteomes and major macromolecular complexes of cyanobacterial origin.

plant biology↗

bioRxiv2026

Structure determination and dual targeting of a plant TACO1 identifies its ancient role as an organelle translation regulator

Ribosome stalling caused by polyproline (PPs) motifs is common. Their translation is enhanced by accessory proteins such as YebC in bacteria, whose homolog, TRANSLATIONAL ACTIVATOR OF CYTOCHROME C OXIDASE 1 (TACO1), aids the translation of mitochondria-encoded proteins. The prevalence of PP motifs across plastid-encoded genes and their impact on the translation of photosynthesis-relevant proteins remains unexplored. Equally, a translation-enhancer of PP motifs equivalent to TACO1 for plastid ribosomes has not been reported. Here, we show that plastid genomes encode 24 proteins with a minimum of one PP motif on average, half of which are conserved in their cyanobacterial homologs, and that the vast majority of eukaryotes, including plants, encode a single TACO1 that we demonstrate to be dually targeted to mitochondria and plastids of Marchantia polymorpha. We resolved the MpTACO1 structure at 2.34 [A] by X-ray crystallography and the flexibility by small-angle X-ray scattering. Through modelling, we demonstrate that MpTACO1 can fit into the peptidyl transfer centre of plant chlororibosomes in a similar manner as human TACO1 in the mitoribosome. The identification and structure determination of the first plastid-targeted YebC/TACO1 allows us to sketch a unified model for the function and evolution of this ancient family of ribosomal accessory proteins, underscoring their indispensable role in the translation of bioenergetic membrane proteins reaching back almost 4 billion years. HighlightsO_LIDozens of GC-rich polyproline (PP) encoding regions are retained by AT-rich genomes C_LIO_LIPP motif conservation hints at regulatory mechanisms and required translation pauses C_LIO_LIChloroplast targeting of a (mitochondrial) translation enhancer of PP motifs C_LIO_LIMpTACO1 structure at 2.34 [A] resolution demonstrates its high level of conservation C_LI

plant biology↗

bioRxiv2026

Codon degeneracy contributes to divergent fitness effects of rare tRNAs with A-starting anticodons

Transfer RNA (tRNA) repertoires vary greatly across genomes, shaped by genetic drift and selection. A peculiar pattern across prokaryotes is the near-complete absence of tRNAs with unmodified adenine at the 34th (wobble) position (i.e., tRNAANN). Each of these tRNAs are just a single mutation away from several other tRNAs. Hence, their persistent absence suggests fundamental but hitherto unclear constraints. We engineered 36 Escherichia coli strains expressing tRNAs carrying each theoretically possible ANN anticodon to determine their functionality and fitness effects. Notably, there was no evidence of broad toxicity due to these tRNAs. All five tRNAANN tested underwent post-transcriptional maturation and all seven tested compensated for the deletion of their respective native tRNABNN (carrying G, C or U at the 34th position), demonstrating that tRNAANN are translationally active. Furthermore, tRNAANN from four-fold degenerate (4D) codon boxes were unmodified and were generally neutral or beneficial, whereas tRNAANN from two-fold degenerate (2D) boxes underwent A34-to-I34 modification and were more likely to impair fitness. We suggest superwobbling by tRNAANN -- decoding an entire four-codon set -- as one mechanism underlying these differential fitness effects. Maximal degeneracy in 4D boxes buffers or exploits tRNAANN superwobbling via synonymous decoding, whereas constrained degeneracy in 2D boxes renders it deleterious, likely through amino acid misincorporation. Thus, these differential fitness effects, sharpens the paradox of neutral or beneficial yet absent 4D tRNAANN, while beginning to empirically unravel underlying causes for the absence of 2D tRNAANN.

evolutionary biology↗

bioRxiv2026

Alternative splicing of a TPR domain determines mitochondrial versus plastid function of the only CLU family protein in Marchantia polymorpha

In plant cells, the multi-domain proteins FRIENDLY and REC regulate the cellular organization, distribution and proliferation of mitochondria and plastids, respectively. Both proteins share a similar overall domain architecture and belong to the larger CLUSTERED MITOCHONDRIA (CLU) superfamily. Domains of CLU proteins have been shown to interact with translation related proteins, tRNA synthetases and even mRNA, but their exact modes of operation remain cryptic and how organelle specificity of CLU paralogs in plant cells is achieved unknown. We characterized the single CLU family protein of the liverwort Marchantia polymorpha that we demonstrate to be transcribed either with or without exon 22, which changes the configuration of the TPR domains in the C-terminus. Knockout of MpCLU affects both mitochondria and plastids, and independent rescues show that the splice variant with exon 22 (MpCLU22) serves mitochondrial- and the one lacking exon 22 (MpCLUspl22) plastid biology. The CLU-C domain of the protein is responsible for nuclear localisation and expressed alone induces a phenotype that differs in photosynthesis performance and transcriptome changes from that of the knockout of MpCLU. Our results identify the C-terminal TPR motif to be responsible for organelle specificity in plants and they provide an example of how genome reformatting and gene loss can be compensated for by the alternative splicing of a single exon.

evolutionary biology↗

bioRxiv2025

SWI3 regulates male sex determination in Marchantia polymorpha

Land plants alternate between multicellular haploid and diploid phases, a life cycle requiring tight coordination between vegetative growth and sexual reproduction. Chromatin regulators such as SWI3, a core subunit of the SWI/SNF complex, are ancestral and highly diversified in angiosperms. As their functions outside of angiosperms remain unclear, we investigated SWI3 of the liverwort Marchantia polymorpha, a non-vascular dioecious land plant. A mutation in the promoter of MpSWI3 affected gametangiophore development and spermiogenesis in males, revealing its male-specific role in reproductive development. The MpSWI3 mutant line amplifies vegetative propagation in males under conditions that would normally induce reproductive growth. The phenotype was underpinned by transcriptomic changes, showing that MpSWI3 modulates key regulators of gametangiophore initiation (e.g. BONOBO, GLID), sperm development and motility (e.g. DUO1, PKAR), and asexual reproduction (e.g. KAI2). Together, this positions MpSWI3 as a chromatin-level regulator balancing vegetative and reproductive phases, highlighting an ancient epigenetic function that coordinates developmental phase transitions in land plants.

plant biology↗

bioRxiv2025

Evolutionary refinement of mitochondrial and plastid targeting sequences coincides with the late diversification of land plants

Plastids and mitochondria are key to plant survival and adaptation. The evolutionary progress of land plants (embryophytes) witnessed gene and genome duplications, and the expansion of organelle-localised proteins. To deal with the increase of nuclear-encoded proteins, targeting to and import by the mitochondrion and plastid is known to have adapted in multiple ways. It included the addition of entire new import channels and lineage-specific import receptors. Through comparative genomics and experimental biology, we uncover further changes of the organelle import machineries. Their evolution likely served to enhance the rate of protein import and improved its physiological regulation, e.g. via interactions between the import channel and respiratory complex. On the cargo side, nuclear-encoded N-terminal targeting sequences of mitochondrial (mNTS) and plastidal (pNTS) proteins diverged in their charge via a preference for phosphorylatable amino acids (adding negative charges after phosphorylation) and an avoidance of positive charges in the pNTS, which is most evident in eudicots. Using Chlamydomonas and Marchantia, we experimentally underscore that the evolved NTS divergence prevents mis-sorting between mitochondria and plastids. In line with the increase of phosphorylatable amino acids in the pNTS, we pinpoint the embryophytic origin of a membrane-anchored phosphatase, PAP2, that is associated with targeting sequence processing. On the whole, we propose a revised model for plant organelle protein import evolution from algae to angiosperms, which facilitated flourishing of this lineage on the land.

evolutionary biology↗

bioRxiv2023

A cautionary tale on organelle proteome prediction algorithms: limits and opportunities

Mitochondria and plastids import thousands of proteins. Their experimental localisation remains a frequent task, but can be resource-intensive and sometimes impossible. Hence, hundreds of studies make use of algorithms that predict a localisation based on a proteins sequence. Their reliability across evolutionary diverse species is unknown. Here, we evaluate the performance of common algorithms (TargetP, Localizer and WoLFPSORT) for four photosynthetic eukaryotes for which experimental plastid and mitochondrial proteome data is available, and 171 eukaryotes using orthology inferences. The match between predictions and experimental data ranges from 75% to as low as 2%. Results worsen as the evolutionary distance between training and query species increases, especially for plant mitochondria for which performance borders on random sampling. Specificity, sensitivity and precision analyses highlight cross-organelle errors and uncover the evolutionary divergence of organelles as the main driver of current performance issues. The results encourage to train the next generation of neural networks on an evolutionary more diverse set of organelle proteins for optimizing performance and reliability.

plant biology↗

bioRxiv2023

A molecular atlas of plastid and mitochondrial adaptations across the evolution from chlorophyte algae to angiosperms

Algae and plants carry two organelles of endosymbiotic origin that have been co-evolving in their host cells for more than a billion years. The biology of plastids and mitochondria can differ significantly across major lineages and organelle changes likely accompanied the adaptation to new ecological niches such as the terrestrial habitat. Based on organelle proteome data and the genomes of 168 phototrophic (Archaeplastida) versus a broad range of 518 non-phototrophic eukaryotes, we screened for changes in plastid and mitochondrial biology across one billion years of evolution. Taking into account 331,571 protein families (or orthogroups), we identify 31,625 protein families that are unique to primary plastid-bearing eukaryotes. 1906 and 825 protein families are predicted to operate in plastids and mitochondria, respectively. Tracing the evolutionary history of these protein families through evolutionary time uncovers the significant remodeling the organelles experienced from algae to land plants. The analyses of gained orthogroups identifies molecular adaptations of organelle biology that connect to the diversification of major lineages and facilitated major transitions from chlorophytes en route to the global greening and origin of angiosperms.

evolutionary biology↗

bioRxiv2022

The layered costs and benefits of translational redundancy

The rate and accuracy of translation hinges upon multiple components - including transfer RNA (tRNA) pools, tRNA modifying enzymes, and rRNA molecules - many of which are redundant in terms of gene copy number or function. It has been hypothesized that the redundancy evolves under selection, driven by its impacts on growth rate. However, we lack empirical measurements of the fitness costs and benefits of redundancy, and we have poor understanding of how this redundancy is organized across components. We manipulated redundancy in multiple translation components of Escherichia coli by deleting 28 tRNA genes, 3 tRNA modifying systems, and 4 rRNA operons in various combinations. We find that redundancy in tRNA pools is beneficial when nutrients are plentiful, and costly under nutrient limitation. This nutrient-dependent cost of redundant tRNA genes stems from upper limits to translation capacity and growth rate, and therefore varies as a function of the maximum growth rate attainable in a given nutrient niche. The loss of redundancy in rRNA genes and tRNA modifying enzymes had similar nutrient-dependent fitness consequences. Importantly, these effects are also contingent upon interactions across translation components, indicating a layered hierarchy from copy number of tRNA and rRNA genes to their expression and posttranscriptional modification. Overall, our results indicate both positive and negative selection on redundancy in translation components, depending on a species evolutionary history with feasts and famines.

evolutionary biology↗

bioRxiv2022

Loss of plastid developmental genes coincides with a reversion to monoplastidy in hornworts

The first plastid evolved from an endosymbiotic cyanobacterium in the common ancestor of the Archaeplastida. The transformative steps from cyanobacterium to organelle included the transfer of control over developmental processes; a necessity for the host to orchestrate, for example, the fission of the organelle. The plastids of almost all embryophytes divide independent from nuclear division, leading to cells housing multiple plastids. Hornworts, however, are monoplastidic (or near-monoplastidic) and their photosynthetic organelles are a curious exception among embryophytes for reasons such as the occasional presence of pyrenoids. Here we screened genomic and transcriptomic data of eleven hornworts for components of plastid developmental pathways. We find intriguing differences among hornworts and specifically highlight that pathway components involved in regulating plastid development and biogenesis were differentially lost in this group of bryophytes. In combination with ancestral state reconstruction, our data suggest that hornworts have reverted back to a monoplastidic phenotype due to the combined loss of two plastid division-associated genes: ARC3 and FtsZ2.

evolutionary biology↗

bioRxiv2020

THE IMPACT OF MISTRANSLATION ON PHENOTYPIC VARIABILITY AND FITNESS

Phenotypic variation is widespread in natural populations, and can significantly alter their ecology and evolution. Phenotypic variation often reflects underlying genetic variation, but also manifests via non-heritable mechanisms. For instance, translation errors result in about 10% of cellular proteins carrying altered sequences. Thus, proteome diversification arising from translation errors can potentially generate phenotypic variability, in turn increasing variability in the fate of cells or of populations. However, this link remains unverified. We manipulated mistranslation levels in Escherichia coli, and measured phenotypic variability between single cells (individual level variation), as well as replicate populations (population level variation). Monitoring growth and survival, we find that mistranslation indeed increases variation across E. coli cells, but does not consistently increase variability in growth parameters across replicate populations. Interestingly, although any deviation from the wild type (WT) level of mistranslation reduces fitness in an optimal environment, the increased variation is associated with a survival benefit under stress. Hence, we suggest that mistranslation-induced phenotypic variation can impact growth and survival and has the potential to alter evolutionary trajectories.

evolutionary biology↗

bioRxiv2019

Global mistranslation facilitates sampling of beneficial mutations under stress

Mistranslation is typically deleterious, but can sometimes be beneficial. Although a specific mistranslated protein can confer a short-term benefit in a particular environment, the prevalence of high global mistranslation rates remains puzzling given the large overall cost. Here, we show that generalized mistranslation enhances early E. coli survival under various forms of DNA damage, because it leads to early activation of the DNA damage-induced SOS response. Mistranslating cells therefore maintain larger populations, facilitating later sampling of critical beneficial mutations. Thus, under DNA damage, both basal and induced mistranslation (through genetic or environmental means) increase the number of genetically resistant and phenotypically persistent cells. Surprisingly, mistranslation also increases survival at high temperature. This wide-ranging stress resistance relies on Lon protease, which is revealed as a key effector that induces the SOS response in addition to alleviating proteotoxic stress. The new links between error-prone protein synthesis, DNA damage, and generalised stress resistance indicate surprising coordination between intracellular stress responses, and suggest a novel hypothesis to explain high global mistranslation rates.

evolutionary biology↗