Biology subjects

Sanchez-Puerta, M. V.

Publications and source records attributed to Sanchez-Puerta, M. V..

8 recordsLinked to original sources

bioRxiv2026

Extensive mitogenome divergence across the Rafflesiaceae in size and impact of horizontal gene transfer

Horizontal gene transfer (HGT) drives organellar evolution, particularly in parasitic plants where host connections facilitate extensive DNA exchange. However, how these processes intersect with cellular machinery to reshape mitogenomic architecture remains poorly understood. Here, we investigate the mechanisms governing structural plasticity and asymmetric host-DNA integration in the extreme holoparasitic family Rafflesiaceae. By performing a comprehensive comparative analysis across all three extant genera (Sapria, Rhizanthes, and Rafflesia) and their Tetrastigma host lineage, we discovered extraordinary mitogenome size divergence, ranging from the expanded 824-kb genome of Sapria (40 circular chromosomes) to the streamlined 282-kb genome of Rhizanthes (35 circular chromosomes). Strikingly, these closely related genera display a total lack of chromosomal synteny, which we link to the ancestral loss of key recombination surveillance genes (RECX, ODB1). Furthermore, while all three genera strictly conserve an identical core of 30 protein-coding genes, host-derived HGT is highly asymmetric, ranging from minimal in Rhizanthes to 60% in Sapria. In Sapria, foreign tracts are sequestered into 15 predominantly non-coding circular chromosomes, a structural arrangement that aligns with the circle-mediated HGT model validated in other holoparasites. Collectively, these parallel patterns across phylogenetically distant lineages demonstrate that sorting and maintaining foreign DNA in autonomous circular blocks is a convergent architectural outcome of massive host-to-parasite genetic transfers. SIGNIFICANCE STATEMENTHorizontal gene transfer is widespread in the nuclear genome of the parasitic plant family Rafflesiaceae, but its contribution to mitochondrial genome evolution has been assessed through the analyses of a limited number of genes. By comparing complete mitochondrial genomes of the parasites and their hosts, we found that closely related species evolved dramatically different genome architectures through distinct mechanisms: one lineage accumulated large amounts of host-derived DNA, whereas another expanded through the proliferation of repetitive sequences with limited contribution from foreign DNA. These findings show that different evolutionary processes can generate profoundly divergent mitochondrial genomes even among closely related parasitic plants.

plant biology↗

bioRxiv2026

Plastome convergence across heterotrophic plant lineages: genome reduction, extreme AT bias, high substitution rates, and functional persistence in the endoparasitic Mitrastemonaceae

The loss of photosynthesis triggers extreme plastid genome (ptDNA) decay, including complete genome loss. Of the multiple transitions to heterotrophy among angiosperms, the ptDNA status remains poorly defined in lineages such as the endophytic Mitrastemonaceae (Ericales). Adopting a panplastome perspective, we characterized genomic variation across Mitrastemon yamamotoi individuals, assembling two complete circular ptDNAs and re-evaluating all available genomic resources for the genus. Our results reveal a highly minimized ptDNA (18-26 kb) with extreme AT content (>77%) and loss of the typical quadripartite architecture. Despite the absence of the stabilizing inverted repeats, the Mitrastemon panplastome exhibits remarkable structural stability and collinearity among individuals. The reduced suite of 26 genes, which includes accD, infA, clpP, ycf1, ycf2, and the essential tetrapyrrole precursor trnE-UUC, exhibit elevated substitution rates. Evolutionary rate analyses (dN/dS) demonstrate that the core ribosomal suite remains under strong purifying selection ({omega}<1), confirming the organelles functional status. Furthermore, transcriptomic analysis identified a nearly complete set of nuclear-encoded DNA-RRR genes, with the notable exception of the MUTS2 surveillance system. The convergent loss of these homologs in Mitrastemon and another holoparasitic lineage may be linked to the shared structural instability and mutational bias. Our findings demonstrate that despite extreme genome compaction, accelerated substitution rates, and severe AT-bias, the Mitrastemon panplastome remains quite stable, providing a definitive genomic framework for understanding plastid evolution within the endoparasitic Mitrastemonaceae.

evolutionary biology↗

bioRxiv2025

Circle-Mediated HGT shapes the multichromosomal mitochondrial genome of the endoparasite Mitrastemon yamamotoi

Horizontal gene transfer (HGT), a well-established driver of genome evolution in prokaryotes, was historically considered rare in plants. However, accumulating genomic evidence supports its occurrence in angiosperms, impacting both nuclear and mitochondrial genomes, particularly in parasitic species that establish vascular connections with their hosts. Despite the increasing recognition of HGT in a few clades of parasitic plants (e.g., Balanophoraceae, Rafflesiaceae, and Cynomoriaceae), the underlying mechanisms and evolutionary consequences of these transfers are still not fully understood. Mitrastemon yamamotoi, a holoparasitic endoparasite in the order Ericales, invades the roots of host trees in the Fagaceae family, creating favorable conditions for HGT. In this study, we assembled for the first time the mtDNA of Mitrastemon, revealing a multipartite structure consisting of 51 circular-mapping chromosomes. Phylogenetic and comparative genomic analyses uncovered extensive HGT from Fagaceae hosts, affecting both coding and non-coding regions. Notably, more than 60% of the Mitrastemon mtDNA is of foreign origin, and seven chromosomes are entirely foreign, with structural signatures in the donor mtDNA consistent with the recently proposed circle-mediated HGT model. Additionally, we detected six protein-coding genes of foreign origin and one chimeric gene. Remarkably, a foreign atp1 gene has replaced the missing native copy and represents a rare event of functional HGT in plant mitochondria. These results position Mitrastemon as a valuable model for studying mtDNA evolution and deepening our understanding of the HGT process. Our findings expand the range of lineages in which circle-mediated HGT has been documented, suggesting it is a more widespread and fundamental mode of mitochondrial HGT in plants. Significant StatementParasitic plants form intimate connections with their hosts, but how these interactions influence genome evolution remains poorly understood. Our study shows that Mitrastemon yamamotoi has acquired over 60% of its mitochondrial DNA from its host through horizontal gene transfer, including entire foreign chromosomes. These findings provide strong support for a recently proposed mechanism, circle-mediated HGT, and suggest that this process may be a more widespread driver of mitochondrial genome evolution in flowering plants.

evolutionary biology↗

bioRxiv2024

Fungal-derived tRNAs are expressed and aminoacylated in orchid mitochondria

Plant mitochondrial genomes (mitogenomes) experience remarkable levels of horizontal gene transfer (HGT), including the recent discovery that orchids anciently acquired DNA from fungal mitogenomes. Thus far, however, there is no evidence that any of the genes from this interkingdom HGT are functional in orchid mitogenomes. Here, we applied a specialized sequencing approach to the orchid Corallorhiza maculata and found that fungal-derived tRNA genes are transcribed, post-transcriptionally modified, and aminoacylated. In contrast, all the transferred protein-coding sequences appear to be pseudogenes. These findings show that fungal HGT has altered the composition of the orchid mitochondrial tRNA pool and suggest that these foreign tRNAs function in translation. The exceptional capacity of tRNAs for HGT and functional replacement is further illustrated by the diversity of tRNA genes in the C. maculata mitogenome, which also include genes of plastid and bacterial origin in addition to their native mitochondrial counterparts.

evolutionary biology↗

bioRxiv2024

The landscape of Arabidopsis tRNA aminoacylation

The function of tRNAs depends on enzymes that cleave primary transcript ends, add a 3' CCA tail, introduce post-transcriptional base modifications, and charge (aminoacylate) mature tRNAs with the correct amino acid. Maintaining an available pool of the resulting aminoacylated tRNAs is essential for protein synthesis. High-throughput sequencing techniques have recently been developed to provide a comprehensive view of aminoacylation state in a tRNA-specific fashion. However, these methods have never been applied to plants. Here, we treated Arabidopsis thaliana RNA samples with periodate and then performed tRNA-seq to distinguish between aminoacylated and uncharged tRNAs. This approach successfully captured every tRNA isodecoder family and detected expression of additional tRNA-like transcripts. We found that estimated aminoacylation rates and CCA tail integrity were significantly higher on average for organellar (mitochondrial and plastid) tRNAs than for nuclear/cytosolic tRNAs. Reanalysis of previously published human cell line data showed a similar pattern. Base modifications result in nucleotide misincorporations and truncations during reverse transcription, which we quantified and used to test for relationships with aminoacylation levels. We also determined that the Arabidopsis tRNA-like sequences (t-elements) that are cleaved from the ends of some mitochondrial mRNAs have post-transcriptionally modified bases and CCA-tail addition. However, these t-elements are not aminoacylated, indicating that they are only recognized by a subset of tRNA-interacting enzymes and do not play a role in translation. Overall, this work provides a characterization of the baseline landscape of plant tRNA aminoacylation rates and demonstrates an approach for investigating environmental and genetic perturbations to plant translation machinery.

molecular biology↗

bioRxiv2023

PHOTOSYNTHESIS DRIVES RETENTION OF BACTERIAL-LIKE TRNA METABOLISM IN PLANT ORGANELLES

Eukaryotic nuclear genomes often encode distinct sets of translation machinery for function in the cytosol vs. organelles (mitochondria and plastids). This raises questions about why multiple translation systems are maintained even though they are capable of comparable functions and whether they evolve differently depending on the compartment where they operate. These questions are particularly interesting in plants because translation machinery, including aminoacyl-tRNA synthetases (aaRS), is often dual-targeted to the plastids and mitochondria. These organelles have different functions, with much higher rates of translation in plastids to supply the abundant, rapid-turnover proteins required for photosynthesis. Previous studies have indicated that plant organellar aaRS evolve more slowly compared to mitochondrial aaRS in eukaryotes that lack plastids. Thus, we investigated the evolution of nuclear-encoded organellar and cytosolic aaRS and tRNA maturation enzymes across a broad sampling of angiosperms, including non-photosynthetic (heterotrophic) plant species with reduced plastid gene expression, to test the hypothesis that translational demands associated with photosynthesis constrain the evolution of enzymes involved in organellar tRNA metabolism. Remarkably, heterotrophic plants exhibited wholesale loss of many organelle-targeted aaRS and other enzymes, even though translation still occurs in their mitochondria and plastids. These losses were often accompanied by apparent retargeting of cytosolic enzymes and tRNAs to the organelles, sometimes preserving aaRS-tRNA charging relationships but other times creating surprising mismatches between cytosolic aaRS and mitochondrial tRNA substrates. Our findings indicate that the presence of a photosynthetic plastid drives the retention of specialized systems for organellar tRNA metabolism. SignificanceThe process by which endosymbionts are integrated into a host and become organelles results in a combination of gene loss, transfer to the nucleus, and retention in the organellar genome. It is not clear why some endosymbiont-derived genes may be retained when a functional host counterpart exists whose gene product could simply be retargeted to the organelles. This study revealed that the photosynthetic activity in plant plastids may be responsible for retention of functionally redundant tRNA processing machinery, while mitochondria are more flexible regarding substitution with cytosolic-type enzymes. Therefore, functional constraint in the plastid is likely more important than in the mitochondria for shaping the evolution and retention of functionally redundant proteins that are dual targeted to both organelles.

plant biology↗

bioRxiv2023

Break-induced replication is the primary recombination pathway in plant somatic hybrid mitochondria: a model for mt-HGT

Somatic hybrids between distant species offer a remarkable model to study genomic recombination events after mitochondrial fusion. Recently, our lab described highly chimeric mitogenomes in two somatic hybrids between the Solanaceae Nicotiana tabacum and Hyoscyamus niger resulting from interparental homologous recombination. To better examine the recombination map in somatic hybrid mitochondria, we developed a more sensitive bioinformatic strategy to detect recombination activity based on high-throughput sequencing without assembling the hybrid mitogenome. We generated a new intergeneric somatic hybrid and re-analyzed the two Solanaceae somatic hybrids. We inferred 213 homologous recombination events across repeats of 2.1 kb on average. Most of them ([~]80%) were asymmetrical, consistent with the break-induced replication (BIR) pathway. Only rare (2.74%) non-homologous events were detected. Interestingly, independent events frequently occurred in the same regions within and across somatic hybrids, suggesting the existence of recombination hotspots in plant mitogenomes. BIR is the main pathway of interparental recombination in somatic hybrid mitochondria. Likewise, under the fusion compatibility model of mitochondrial horizontal transfer, foreign mitochondria fuse with those in the recipient cell and their genomes likely recombine via BIR, resulting in the integration and/or loss of mitochondrial DNA. Findings of this study are also relevant to mitogenome editing assays. HighlightWe show that the chimeric mitochondrial genomes of somatic hybrids result from one of the three described homologous recombination pathways (BIR), mimicking the fusion compatibility model for plant HGT.

molecular biology↗

bioRxiv2018

Elucidating genomic patterns and recombination events in plant cybrid mitochondria

The maintenance of a dynamic equilibrium between the mitochondrial and nuclear genomes requires continuous communication and a high level of compatibility between them, so that alterations in one genetic compartment need adjustments in the other. The co-evolution of nuclear and mitochondrial genomes has been poorly studied, even though the consequences and effects of this interaction are highly relevant for human health, as well as for crop improvement programs and for genetic engineering. The mitochondria of plants represent an excellent system to understand the mechanisms of genomic rearrangements, chimeric gene formation, incompatibility between nucleus and cytoplasm, and horizontal gene transfer. We carried out detailed analyses of the mitochondrial genome (mtDNA) of a repeated cybrid between the solanaceae Nicotiana tabacum and Hyoscyamus niger. The mtDNA of the cybrid was intermediate between the size of parental mtDNAs and the sum of them. Noticeably, most of the homologous sequences inherited from both parents were lost. In contrast, the majority of the sequences exclusive of a single parent were maintained. The mitochondrial gene content included a majority of N. tabacum derived genes, but also chimeric, two-parent derived, and H. niger-derived genes in a tobacco nuclear background. Any of these alterations in the gene content could be the cause of CMS in the cybrid. The parental mtDNAs interacted through 28 homologous recombination events and a single case of illegitimate recombination. Three main homologous recombination mechanisms were recognized in the cybrid mitochondria. Break induced replication (BIR) pathway was the most frequent. We propose that BIR could be one of the mechanisms responsible for the loss of the majority of the repeated regions derived from H. niger.

molecular biology↗