Different rates of spontaneous mutation of chloroplastic and nuclear viroids as determined by high-fidelity ultra-deep sequencing

[EN] Mutation rates vary by orders of magnitude across biological systems, being higher for simpler genomes. The simplest known genomes correspond to viroids, subviral plant replicons constituted by circular non-coding RNAs of few hundred bases. Previous work has revealed an extremely high mutation rate for chrysanthemum chlorotic mottle viroid, a chloroplastreplicating viroid. However, whether this is a general feature of viroids remains unclear. Here, we have used high-fidelity ultra-deep sequencing to determine the mutation rate in a common host (eggplant) of two viroids, each representative of one family: the chloroplastic eggplant latent viroid (ELVd, Avsunviroidae) and the nuclear potato spindle tuber viroid (PSTVd, Pospiviroidae). This revealed higher mutation frequencies in ELVd than in PSTVd, as well as marked differences in the types of mutations produced. Rates of spontaneous mutation, quantified in vivo using the lethal mutation method, ranged from 1/1000 to 1/800 for ELVd and from 1/7000 to 1/3800 for PSTVd depending on sequencing run. These results suggest that extremely high mutability is a common feature of chloroplastic viroids, whereas the mutation rates of PSTVd and potentially other nuclear viroids appear significantly lower and closer to those of some RNA viruses.This work was supported by the European Research Council (erc.europa.eu; ERC-2011-StG-281191-VIRMUT to RS), the Spanish Ministerio de Economia y Competitividad (www.mineco.gob.es; BFU2013-41329 grant to RS, BFU2014-56812-P grant to RF, and a predoctoral fellowship to ALC), and the Spanish Junta de Comunidades de Castilla-La Mancha (www.castillalamancha.es;postdoctoral fellowship to CB). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.López-Carrasco, MA.; Ballesteros Martínez, C.; Sentandreu, V.; Delgado Villar, SG.; Gago Zachert, SP.; Flores Pedauye, R.; Sanjuan Verdeguer, R. (2017). Different rates of spontaneous mutation of chloroplastic and nuclear viroids as determined by high-fidelity ultra-deep sequencing. PLoS Pathogens. 13(9):1-17. https://doi.org/10.1371/journal.ppat.1006547S117139Ganai, R. A., & Johansson, E. (2016). DNA Replication—A Matter of Fidelity. Molecular Cell, 62(5), 745-755. doi:10.1016/j.molcel.2016.05.003Lynch, M. (2010). Evolution of the mutation rate. Trends in Genetics, 26(8), 345-352. doi:10.1016/j.tig.2010.05.003Sanjuán, R., & Domingo-Calap, P. (2016). Mechanisms of viral mutation. Cellular and Molecular Life Sciences, 73(23), 4433-4448. doi:10.1007/s00018-016-2299-6Gago, S., Elena, S. F., Flores, R., & Sanjuan, R. (2009). Extremely High Mutation Rate of a Hammerhead Viroid. Science, 323(5919), 1308-1308. doi:10.1126/science.1169202Flores, R., Gago-Zachert, S., Serra, P., Sanjuán, R., & Elena, S. F. (2014). Viroids: Survivors from the RNA World? Annual Review of Microbiology, 68(1), 395-414. doi:10.1146/annurev-micro-091313-103416Flores, R., Minoia, S., Carbonell, A., Gisel, A., Delgado, S., López-Carrasco, A., … Di Serio, F. (2015). Viroids, the simplest RNA replicons: How they manipulate their hosts for being propagated and how their hosts react for containing the infection. Virus Research, 209, 136-145. doi:10.1016/j.virusres.2015.02.027Steger, G., & Perreault, J.-P. (2016). Structure and Associated Biological Functions of Viroids. Advances in Virus Research, 141-172. doi:10.1016/bs.aivir.2015.11.002Diener, T. O. (1989). Circular RNAs: relics of precellular evolution? Proceedings of the National Academy of Sciences, 86(23), 9370-9374. doi:10.1073/pnas.86.23.9370Ambrós, S., Hernández, C., & Flores, R. (1999). Rapid generation of genetic heterogeneity in progenies from individual cDNA clones of peach latent mosaic viroid in its natural host The data reported in this paper are in the EMBL nucleotide sequence database and assigned the accession nos AJ241818–AJ241850. Journal of General Virology, 80(8), 2239-2252. doi:10.1099/0022-1317-80-8-2239Navarro, J.-A., Vera, A., & Flores, R. (2000). A Chloroplastic RNA Polymerase Resistant to Tagetitoxin Is Involved in Replication of Avocado Sunblotch Viroid. Virology, 268(1), 218-225. doi:10.1006/viro.1999.0161Rodio, M.-E., Delgado, S., De Stradis, A., Gómez, M.-D., Flores, R., & Di Serio, F. (2007). A Viroid RNA with a Specific Structural Motif Inhibits Chloroplast Development. The Plant Cell, 19(11), 3610-3626. doi:10.1105/tpc.106.049775Carbonell, A., De la Peña, M., Flores, R., & Gago, S. (2006). Effects of the trinucleotide preceding the self-cleavage site on eggplant latent viroid hammerheads: differences in co- and post-transcriptional self-cleavage may explain the lack of trinucleotide AUC in most natural hammerheads. Nucleic Acids Research, 34(19), 5613-5622. doi:10.1093/nar/gkl717Hutchins, C. J., Rathjen, P. D., Forster, A. C., & Symons, R. H. (1986). Self-cleavage of plus and minus RNA transcripts of avocado sunblotch viroid. Nucleic Acids Research, 14(9), 3627-3640. doi:10.1093/nar/14.9.3627PRODY, G. A., BAKOS, J. T., BUZAYAN, J. M., SCHNEIDER, I. R., & BRUENING, G. (1986). Autolytic Processing of Dimeric Plant Virus Satellite RNA. Science, 231(4745), 1577-1580. doi:10.1126/science.231.4745.1577Nohales, M.-A., Molina-Serrano, D., Flores, R., & Daros, J.-A. (2012). Involvement of the Chloroplastic Isoform of tRNA Ligase in the Replication of Viroids Belonging to the Family Avsunviroidae. Journal of Virology, 86(15), 8269-8276. doi:10.1128/jvi.00629-12Branch, A. D., Benenfeld, B. J., & Robertson, H. D. (1988). Evidence for a single rolling circle in the replication of potato spindle tuber viroid. Proceedings of the National Academy of Sciences, 85(23), 9128-9132. doi:10.1073/pnas.85.23.9128Daros, J.-A., & Flores, R. (2004). Arabidopsis thaliana has the enzymatic machinery for replicating representative viroid species of the family Pospiviroidae. Proceedings of the National Academy of Sciences, 101(17), 6792-6797. doi:10.1073/pnas.0401090101Feldstein, P. A., Hu, Y., & Owens, R. A. (1998). Precisely full length, circularizable, complementary RNA: An infectious form of potato spindle tuber viroid. Proceedings of the National Academy of Sciences, 95(11), 6560-6565. doi:10.1073/pnas.95.11.6560Gas, M.-E., Hernández, C., Flores, R., & Daròs, J.-A. (2007). Processing of Nuclear Viroids In Vivo: An Interplay between RNA Conformations. PLoS Pathogens, 3(11), e182. doi:10.1371/journal.ppat.0030182Nohales, M.-A., Flores, R., & Daros, J.-A. (2012). Viroid RNA redirects host DNA ligase 1 to act as an RNA ligase. Proceedings of the National Academy of Sciences, 109(34), 13805-13810. doi:10.1073/pnas.1206187109Brass, J. R. J., Owens, R. A., Matoušek, J., & Steger, G. (2017). Viroid quasispecies revealed by deep sequencing. RNA Biology, 14(3), 317-325. doi:10.1080/15476286.2016.1272745Bull, J. J., Sanjuán, R., & Wilke, C. O. (2007). Theory of Lethal Mutagenesis for Viruses. Journal of Virology, 81(6), 2930-2939. doi:10.1128/jvi.01624-06Cuevas, J. M., González-Candelas, F., Moya, A., & Sanjuán, R. (2009). Effect of Ribavirin on the Mutation Rate and Spectrum of Hepatitis C Virus In Vivo. Journal of Virology, 83(11), 5760-5764. doi:10.1128/jvi.00201-09Ribeiro, R. M., Li, H., Wang, S., Stoddard, M. B., Learn, G. H., Korber, B. T., … Perelson, A. S. (2012). Quantifying the Diversification of Hepatitis C Virus (HCV) during Primary Infection: Estimates of the In Vivo Mutation Rate. PLoS Pathogens, 8(8), e1002881. doi:10.1371/journal.ppat.1002881Acevedo, A., Brodsky, L., & Andino, R. (2013). Mutational and fitness landscapes of an RNA virus revealed through population sequencing. Nature, 505(7485), 686-690. doi:10.1038/nature12861Cuevas, J. M., Geller, R., Garijo, R., López-Aldeguer, J., & Sanjuán, R. (2015). Extremely High Mutation Rate of HIV-1 In Vivo. PLOS Biology, 13(9), e1002251. doi:10.1371/journal.pbio.1002251Acevedo, A., & Andino, R. (2014). Library preparation for highly accurate population sequencing of RNA viruses. Nature Protocols, 9(7), 1760-1769. doi:10.1038/nprot.2014.118Kennedy, S. R., Schmitt, M. W., Fox, E. J., Kohrn, B. F., Salk, J. J., Ahn, E. H., … Loeb, L. A. (2014). Detecting ultralow-frequency mutations by Duplex Sequencing. Nature Protocols, 9(11), 2586-2606. doi:10.1038/nprot.2014.170Franklin, R. M. (1966). Purification and properties of the replicative intermediate of the RNA bacteriophage R17. Proceedings of the National Academy of Sciences, 55(6), 1504-1511. doi:10.1073/pnas.55.6.1504López-Carrasco, A., Gago-Zachert, S., Mileti, G., Minoia, S., Flores, R., & Delgado, S. (2015). The transcription initiation sites of eggplant latent viroid strands map within distinct motifs in theirin vivoRNA conformations. RNA Biology, 13(1), 83-97. doi:10.1080/15476286.2015.1119365Keese, P., & Symons, R. H. (1985). Domains in viroids: evidence of intermolecular RNA rearrangements and their contribution to viroid evolution. Proceedings of the National Academy of Sciences, 82(14), 4582-4586. doi:10.1073/pnas.82.14.4582López-Carrasco, A., & Flores, R. (2016). Dissecting the secondary structure of the circular RNA of a nuclear viroid in vivo: A «naked» rod-like conformation similar but not identical to that observed in vitro. RNA Biology, 14(8), 1046-1054. doi:10.1080/15476286.2016.1223005Flores, R., Hernandez, C., de la Peña, M., Vera, A., & Daros, J.-A. (2001). Hammerhead Ribozyme Structure and Function in Plant RNA Replication. Ribonucleases - Part A, 540-552. doi:10.1016/s0076-6879(01)41175-xMartick, M., & Scott, W. G. (2006). Tertiary Contacts Distant from the Active Site Prime a Ribozyme for Catalysis. Cell, 126(2), 309-320. doi:10.1016/j.cell.2006.06.036Ruffner, D. E., Stormo, G. D., & Uhlenbeck, O. C. (1990). Sequence requirements of the hammerhead RNA self-cleavage reaction. Biochemistry, 29(47), 10695-10702. doi:10.1021/bi00499a018Flores, R., Serra, P., Minoia, S., Di Serio, F., & Navarro, B. (2012). Viroids: From Genotype to Phenotype Just Relying on RNA Sequence and Structural Motifs. Frontiers in Microbiology, 3. doi:10.3389/fmicb.2012.00217Owens, R. A., Chen, W., Hu, Y., & Hsu, Y.-H. (1995). Suppression of Potato Spindle Tuber Viroid Replication and Symptom Expression by Mutations Which Stabilize the Pathogenicity Domain. Virology, 208(2), 554-564. doi:10.1006/viro.1995.1186Takeda, R., Petrov, A. I., Leontis, N. B., & Ding, B. (2011). A Three-Dimensional RNA Motif in Potato spindle tuber viroid Mediates Trafficking from Palisade Mesophyll to Spongy Mesophyll in Nicotiana benthamiana. The Plant Cell, 23(1), 258-272. doi:10.1105/tpc.110.081414Zhong, X., Leontis, N., Qian, S., Itaya, A., Qi, Y., Boris-Lawrie, K., & Ding, B. (2006). Tertiary Structural and Functional Analyses of a Viroid RNA Motif by Isostericity Matrix and Mutagenesis Reveal Its Essential Role in Replication. Journal of Virology, 80(17), 8566-8581. doi:10.1128/jvi.00837-06Zhong, X., Tao, X., Stombaugh, J., Leontis, N., & Ding, B. (2007). Tertiary structure and function of an RNA motif required for plant vascular entry to initiate systemic trafficking. The EMBO Journal, 26(16), 3836-3846. doi:10.1038/sj.emboj.7601812Zhong, X., Archual, A. J., Amin, A. A., & Ding, B. (2008). A Genomic Map of Viroid RNA Motifs Critical for Replication and Systemic Trafficking. The Plant Cell, 20(1), 35-47. doi:10.1105/tpc.107.056606Thomas, M. J., Platas, A. A., & Hawley, D. K. (1998). Transcriptional Fidelity and Proofreading by RNA Polymerase II. Cell, 93(4), 627-637. doi:10.1016/s0092-8674(00)81191-5Gout, J.-F., Thomas, W. K., Smith, Z., Okamoto, K., & Lynch, M. (2013). Large-scale detection of in vivo transcription errors. Proceedings of the National Academy of Sciences, 110(46), 18584-18589. doi:10.1073/pnas.1309843110Hedtke, B. (1997). Mitochondrial and Chloroplast Phage-Type RNA Polymerases in Arabidopsis. Science, 277(5327), 809-811. doi:10.1126/science.277.5327.809Lerbs-Mache, S. (1993). The 110-kDa polypeptide of spinach plastid DNA-dependent RNA polymerase: single-subunit enzyme or catalytic core of multimeric enzyme complexes? Proceedings of the National Academy of Sciences, 90(12), 5509-5513. doi:10.1073/pnas.90.12.5509Oldenkott, B., Yamaguchi, K., Tsuji-Tsukinoki, S., Knie, N., & Knoop, V. (2014). Chloroplast RNA editing going extreme: more than 3400 events of C-to-U editing in the chloroplast transcriptome of the lycophyteSelaginella uncinata. RNA, 20(10), 1499-1506. doi:10.1261/rna.045575.114Codoñer, F. M., Darós, J.-A., Solé, R. V., & Elena, S. F. (2006). The Fittest versus the Flattest: Experimental Confirmation of the Quasispecies Effect with Subviral Pathogens. PLoS Pathogens, 2(12), e136. doi:10.1371/journal.ppat.0020136Eigen, M. (1971). Selforganization of matter and the evolution of biological macromolecules. Die Naturwissenschaften, 58(10), 465-523. doi:10.1007/bf00623322Lynch, M. (2011). The Lower Bound to the Evolution of Mutation Rates. Genome Biology and Evolution, 3, 1107-1118. doi:10.1093/gbe/evr066Bradwell, K., Combe, M., Domingo-Calap, P., & Sanjuán, R. (2013). Correlation Between Mutation Rate and Genome Size in Riboviruses: Mutation Rate of Bacteriophage Qβ. Genetics, 195(1), 243-251. doi:10.1534/genetics.113.154963Drake, J. W. (1991). A constant rate of spontaneous mutation in DNA-based microbes. Proceedings of the National Academy of Sciences, 88(16), 7160-7164. doi:10.1073/pnas.88.16.7160Schmitt, M. W., Kennedy, S. R., Salk, J. J., Fox, E. J., Hiatt, J. B., & Loeb, L. A. (2012). Detection of ultra-rare mutations by next-generation sequencing. Proceedings of the National Academy of Sciences, 109(36), 14508-14513. doi:10.1073/pnas.120871510

Involvement of the Chloroplastic Isoform of tRNA Ligase in the Replication of Viroids Belonging to the Family Avsunviroidae

Avocado sunblotch viroid, peach latent mosaic viroid, chrysanthemum chlorotic mottle viroid, and eggplant latent viroid (ELVd), the four recognized members of the family Avsunviroidae, replicate through the symmetric pathway of an RNA-to-RNA rolling-circle mechanism in chloroplasts of infected cells. Viroid oligomeric transcripts of both polarities contain embedded hammerhead ribozymes that, during replication, mediate their self-cleavage to monomeric-length RNAs with 5'-hydroxyl and 2',3'-phosphodiester termini that are subsequently circularized. We report that a recombinant version of the chloroplastic isoform of the tRNA ligase from eggplant (Solanum melongena L.) efficiently catalyzes in vitro circularization of the plus [(+)] and minus [(-)] monomeric linear replication intermediates from the four Avsunviroidae. We also show that while this RNA ligase specifically recognizes the genuine monomeric linear (+) ELVd replication intermediate, it does not do so with five other monomeric linear (+) ELVd RNAs with their ends mapping at different sites along the molecule, despite containing the same 5'-hydroxyl and 2',3'-phosphodiester terminal groups. Moreover, experiments involving transient expression of a dimeric (+) ELVd transcript in Nicotiana benthamiana Domin plants preinoculated with a tobacco rattle virus-derived vector to induce silencing of the plant endogenous tRNA ligase show a significant reduction of ELVd circularization. In contrast, circularization of a viroid replicating in the nucleus occurring through a different pathway is unaffected. Together, these results support the conclusion that the chloroplastic isoform of the plant tRNA ligase is the host enzyme mediating circularization of both (+) and (-) monomeric linear intermediates during replication of the viroids belonging to the family Avsunviroidae.This work was supported by the Ministerio de Ciencia e Innovacion (MICINN) from Spain through grants BIO2008-01986, BIO2011-26741, and BFU2008-03154. M. A. Nohales and D. Molina-Serrano were the recipients of predoctoral fellowships from the Spanish Ministerio de Educacion y Ciencia.Nohales Zafra, MA.; Molina Serrano, D.; Flores Pedauye, R.; Daros Arnau, JA. (2012). Involvement of the Chloroplastic Isoform of tRNA Ligase in the Replication of Viroids Belonging to the Family Avsunviroidae. Journal of Virology. 86:8269-8276. https://doi.org/10.1128/JVI.00629-12S8269827686Abelson, J., Trotta, C. R., & Li, H. (1998). tRNA Splicing. Journal of Biological Chemistry, 273(21), 12685-12688. doi:10.1074/jbc.273.21.12685Branch, A. D., Benenfeld, B. J., & Robertson, H. D. (1988). Evidence for a single rolling circle in the replication of potato spindle tuber viroid. Proceedings of the National Academy of Sciences, 85(23), 9128-9132. doi:10.1073/pnas.85.23.9128Branch, A., & Robertson, H. (1984). A replication cycle for viroids and other small infectious RNA’s. Science, 223(4635), 450-455. doi:10.1126/science.6197756Canny, M. D., Jucker, F. M., & Pardi, A. (2007). Efficient Ligation of theSchistosomaHammerhead Ribozyme†. Biochemistry, 46(12), 3826-3834. doi:10.1021/bi062077rCote, F., Levesque, D., & Perreault, J.-P. (2001). Natural 2’,5’-Phosphodiester Bonds Found at the Ligation Sites of Peach Latent Mosaic Viroid. Journal of Virology, 75(1), 19-25. doi:10.1128/jvi.75.1.19-25.2001Côté, F., & Perreault, J.-P. (1997). Peach latent mosaic viroid is locked by a 2′,5′-phosphodiester bond produced by in vitro self-ligation 1 1Edited by D. E. Draper. Journal of Molecular Biology, 273(3), 533-543. doi:10.1006/jmbi.1997.1355Daros, J.-A. (2002). A chloroplast protein binds a viroid RNA in vivo and facilitates its hammerhead-mediated self-cleavage. The EMBO Journal, 21(4), 749-759. doi:10.1093/emboj/21.4.749Daros, J. A., Marcos, J. F., Hernandez, C., & Flores, R. (1994). Replication of avocado sunblotch viroid: evidence for a symmetric pathway with two rolling circles and hammerhead ribozyme processing. Proceedings of the National Academy of Sciences, 91(26), 12813-12817. doi:10.1073/pnas.91.26.12813De la Pena, M. (2003). Peripheral regions of natural hammerhead ribozymes greatly increase their self-cleavage activity. The EMBO Journal, 22(20), 5561-5570. doi:10.1093/emboj/cdg530De la Pena, M., Navarro, B., & Flores, R. (1999). Mapping the molecular determinant of pathogenicity in a hammerhead viroid: A tetraloop within the in vivo branched RNA conformation. Proceedings of the National Academy of Sciences, 96(17), 9960-9965. doi:10.1073/pnas.96.17.9960Ding, B. (2009). The Biology of Viroid-Host Interactions. Annual Review of Phytopathology, 47(1), 105-131. doi:10.1146/annurev-phyto-080508-081927Englert, M. (2005). Plant tRNA ligases are multifunctional enzymes that have diverged in sequence and substrate specificity from RNA ligases of other phylogenetic origins. Nucleic Acids Research, 33(1), 388-399. doi:10.1093/nar/gki174Englert, M., Latz, A., Becker, D., Gimple, O., Beier, H., & Akama, K. (2007). Plant pre-tRNA splicing enzymes are targeted to multiple cellular compartments. Biochimie, 89(11), 1351-1365. doi:10.1016/j.biochi.2007.06.014Fadda, Z., Daros, J. A., Fagoaga, C., Flores, R., & Duran-Vila, N. (2003). Eggplant Latent Viroid, the Candidate Type Species for a New Genus within the Family Avsunviroidae (Hammerhead Viroids). Journal of Virology, 77(11), 6528-6532. doi:10.1128/jvi.77.11.6528-6532.2003Feldstein, P. A., Hu, Y., & Owens, R. A. (1998). Precisely full length, circularizable, complementary RNA: An infectious form of potato spindle tuber viroid. Proceedings of the National Academy of Sciences, 95(11), 6560-6565. doi:10.1073/pnas.95.11.6560Flores, R., Daròs, J.-A., & Hernández, C. (2000). Avsunviroidae family: Viroids containing hammerhead ribozymes. Advances in Virus Research, 271-323. doi:10.1016/s0065-3527(00)55006-4Flores, R., Hernández, C., Alba, A. E. M. de, Daròs, J.-A., & Serio, F. D. (2005). Viroids and Viroid-Host Interactions. Annual Review of Phytopathology, 43(1), 117-139. doi:10.1146/annurev.phyto.43.040204.140243Flores, R., & Owens, R. A. (2008). Viroids. Encyclopedia of Virology, 332-342. doi:10.1016/b978-012374410-4.00532-xGas, M.-E., Hernández, C., Flores, R., & Daròs, J.-A. (2007). Processing of Nuclear Viroids In Vivo: An Interplay between RNA Conformations. PLoS Pathogens, 3(11), e182. doi:10.1371/journal.ppat.0030182Gas, M.-E., Molina-Serrano, D., Hernandez, C., Flores, R., & Daros, J.-A. (2008). Monomeric Linear RNA of Citrus Exocortis Viroid Resulting from Processing In Vivo Has 5’-Phosphomonoester and 3’-Hydroxyl Termini: Implications for the RNase and RNA Ligase Involved in Replication. Journal of Virology, 82(20), 10321-10325. doi:10.1128/jvi.01229-08Gómez, G., & Pallás, V. (2010). Noncoding RNA Mediated Traffic of Foreign mRNA into Chloroplasts Reveals a Novel Signaling Mechanism in Plants. PLoS ONE, 5(8), e12269. doi:10.1371/journal.pone.0012269Hernandez, C., & Flores, R. (1992). Plus and minus RNAs of peach latent mosaic viroid self-cleave in vitro via hammerhead structures. Proceedings of the National Academy of Sciences, 89(9), 3711-3715. doi:10.1073/pnas.89.9.3711Hertel, K. J., Herschlag, D., & Uhlenbeck, O. C. (1994). A Kinetic and Thermodynamic Framework for the Hammerhead Ribozyme Reaction. Biochemistry, 33(11), 3374-3385. doi:10.1021/bi00177a031Hutchins, C. J., Keese, P., Visvader, J. E., Rathjen, P. D., McInnes, J. L., & Symons, R. H. (1985). Comparison of multimeric plus and minus forms of viroids and virusoids. Plant Molecular Biology, 4(5), 293-304. doi:10.1007/bf02418248Hutchins, C. J., Rathjen, P. D., Forster, A. C., & Symons, R. H. (1986). Self-cleavage of plus and minus RNA transcripts of avocado sunblotch viroid. Nucleic Acids Research, 14(9), 3627-3640. doi:10.1093/nar/14.9.3627Khvorova, A., Lescoute, A., Westhof, E., & Jayasena, S. D. (2003). Sequence elements outside the hammerhead ribozyme catalytic core enable intracellular activity. Nature Structural & Molecular Biology, 10(9), 708-712. doi:10.1038/nsb959Kiberstis, P. A., Haseloff, J., & Zimmern, D. (1985). 2′ phosphomonoester, 3′-5′ phosphodiester bond at a unique site in a circular viral RNA. The EMBO Journal, 4(3), 817-822. doi:10.1002/j.1460-2075.1985.tb03703.xKonarska, M., Filipowicz, W., Domdey, H., & Gross, H. J. (1981). Formation of a 2′-phosphomonoester, 3′,5′-phosphodiester linkage by a novel RNA ligase in wheat germ. Nature, 293(5828), 112-116. doi:10.1038/293112a0Liu, Y., Schiff, M., Marathe, R., & Dinesh-Kumar, S. P. (2002). Tobacco Rar1, EDS1 and NPR1/NIM1 like genes are required for N-mediated resistance to tobacco mosaic virus. The Plant Journal, 30(4), 415-429. doi:10.1046/j.1365-313x.2002.01297.xMakino, S., Sawasaki, T., Endo, Y., & Takai, K. (2005). Purification and sequence determination of an RNA ligase from wheat embryos. Nucleic Acids Symposium Series, 49(1), 319-320. doi:10.1093/nass/49.1.319Marcos, J. F., & Flores, R. (1993). The 5’ end Generated in the in vitro Self-Cleavage Reaction of Avocado Sunblotch Viroid RNAs is Present in Naturally Occurring Linear Viroid Molecules. Journal of General Virology, 74(5), 907-910. doi:10.1099/0022-1317-74-5-907Martinez, F., Marques, J., Salvador, M. L., & Daros, J.-A. (2009). Mutational analysis of eggplant latent viroid RNA processing in Chlamydomonas reinhardtii chloroplast. Journal of General Virology, 90(12), 3057-3065. doi:10.1099/vir.0.013425-0Molina-Serrano, D., Marqués, J., Nohales, M.-Á., Flores, R., & Daròs, J.-A. (2012). A chloroplastic RNA ligase activity analogous to the bacterial and archaeal 2´–5′ RNA ligase. RNA Biology, 9(3), 326-333. doi:10.4161/rna.19218Navarro, B., & Flores, R. (1997). Chrysanthemum chlorotic mottle viroid: Unusual structural properties of a subgroup of self-cleaving viroids with hammerhead ribozymes. Proceedings of the National Academy of Sciences, 94(21), 11262-11267. doi:10.1073/pnas.94.21.11262Navarro, J.-A., Daròs, J.-A., & Flores, R. (1999). Complexes Containing Both Polarity Strands of Avocado Sunblotch Viroid: Identification in Chloroplasts and Characterization. Virology, 253(1), 77-85. doi:10.1006/viro.1998.9497Navarro, J.-A., Vera, A., & Flores, R. (2000). A Chloroplastic RNA Polymerase Resistant to Tagetitoxin Is Involved in Replication of Avocado Sunblotch Viroid. Virology, 268(1), 218-225. doi:10.1006/viro.1999.0161Nelson, J. A., Shepotinovskaya, I., & Uhlenbeck, O. C. (2005). Hammerheads Derived from sTRSV Show Enhanced Cleavage and Ligation Rate Constants†. Biochemistry, 44(44), 14577-14585. doi:10.1021/bi051130tPRODY, G. A., BAKOS, J. T., BUZAYAN, J. M., SCHNEIDER, I. R., & BRUENING, G. (1986). Autolytic Processing of Dimeric Plant Virus Satellite RNA. Science, 231(4745), 1577-1580. doi:10.1126/science.231.4745.1577Rodio, M.-E., Delgado, S., De Stradis, A., Gómez, M.-D., Flores, R., & Di Serio, F. (2007). A Viroid RNA with a Specific Structural Motif Inhibits Chloroplast Development. The Plant Cell, 19(11), 3610-3626. doi:10.1105/tpc.106.049775Ruiz, M. T., Voinnet, O., & Baulcombe, D. C. (1998). Initiation and Maintenance of Virus-Induced Gene Silencing. The Plant Cell, 10(6), 937-946. doi:10.1105/tpc.10.6.937Schurer, H. (2002). A universal method to produce in vitro transcripts with homogeneous 3’ ends. Nucleic Acids Research, 30(12), 56e-56. doi:10.1093/nar/gnf055Tsagris, E. M., Martínez de Alba, Á. E., Gozmanova, M., & Kalantidis, K. (2008). Viroids. Cellular Microbiology, 10(11), 2168-2179. doi:10.1111/j.1462-5822.2008.01231.xWANG, L. K. (2005). Structure-function analysis of yeast tRNA ligase. RNA, 11(6), 966-975. doi:10.1261/rna.217030

Evolution of the use of corticosteroids for the treatment of hospitalised COVID-19 patients in Spain between March and November 2020: SEMI-COVID national registry

Objectives: Since the results of the RECOVERY trial, WHO recommendations about the use of corticosteroids (CTs) in COVID-19 have changed. The aim of the study is to analyse the evolutive use of CTs in Spain during the pandemic to assess the potential influence of new recommendations. Material and methods: A retrospective, descriptive, and observational study was conducted on adults hospitalised due to COVID-19 in Spain who were included in the SEMI-COVID- 19 Registry from March to November 2020. Results: CTs were used in 6053 (36.21%) of the included patients. The patients were older (mean (SD)) (69.6 (14.6) vs. 66.0 (16.8) years; p < 0.001), with hypertension (57.0% vs. 47.7%; p < 0.001), obesity (26.4% vs. 19.3%; p < 0.0001), and multimorbidity prevalence (20.6% vs. 16.1%; p < 0.001). These patients had higher values (mean (95% CI)) of C-reactive protein (CRP) (86 (32.7-160) vs. 49.3 (16-109) mg/dL; p < 0.001), ferritin (791 (393-1534) vs. 470 (236- 996) µg/dL; p < 0.001), D dimer (750 (430-1400) vs. 617 (345-1180) µg/dL; p < 0.001), and lower Sp02/Fi02 (266 (91.1) vs. 301 (101); p < 0.001). Since June 2020, there was an increment in the use of CTs (March vs. September; p < 0.001). Overall, 20% did not receive steroids, and 40% received less than 200 mg accumulated prednisone equivalent dose (APED). Severe patients are treated with higher doses. The mortality benefit was observed in patients with oxygen saturation </=90%. Conclusions: Patients with greater comorbidity, severity, and inflammatory markers were those treated with CTs. In severe patients, there is a trend towards the use of higher doses. The mortality benefit was observed in patients with oxygen saturation </=90%

Biochemical quantitation of the eIF5A hypusination in Arabidopsis thaliana uncovers ABA-dependent regulation

The eukaryotic translation elongation factor eIF5A is the only protein known to contain the unusual amino acid hypusine which is essential for its biological activity. This post-translational modification is achieved by the sequential action of the enzymes deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH). The crucial molecular function of eIF5A during translation has been recently elucidated in yeast and it is expected to be fully conserved in every eukaryotic cell, however the functional description of this pathway in plants is still sparse. The genetic approaches with transgenic plants for either eIF5A overexpression or antisense have revealed some activities related to the control of cell death processes but the molecular details remain to be characterized. One important aspect of fully understanding this pathway is the biochemical description of the hypusine modification system. Here we have used recombinant eIF5A proteins either modified by hypusination or non-modified to establish a bi-dimensional electrophoresis (2D-E) profile for the three eIF5A protein isoforms and their hypusinated or unmodified proteoforms present in Arabidopsis thaliana. The combined use of the recombinant 2D-E profile together with 2D-E/western blot analysis from whole plant extracts has provided a quantitative approach to measure the hypusination status of eIF5A. We have used this information to demonstrate that treatment with the hormone abscisic acid produces an alteration of the hypusine modification system in Arabidopsis thaliana. Overall this study presents the first biochemical description of the post-translational modification of eIF5A by hypusination which will be functionally relevant for future studies related to the characterization of this pathway in Arabidopsis thaliana