Ethylene is Involved in Symptom Development and Ribosomal Stress of Tomato Plants upon Citrus Exocortis Viroid Infection

[EN] Citrus exocortis viroid (CEVd) is known to cause different symptoms in citrus trees, and its mechanism of infection has been studied in tomato as an experimental host, producing ribosomal stress on these plants. Some of the symptoms caused by CEVd in tomato plants resemble those produced by the phytohormone ethylene. The present study is focused on elucidating the relationship between CEVd infection and ethylene on disease development. To this purpose, the ethylene insensitive Never ripe (Nr) tomato mutants were infected with CEVd, and several aspects such as susceptibility to infection, defensive response, ethylene biosynthesis and ribosomal stress were studied. Phenotypic characterization revealed higher susceptibility to CEVd in these mutants, which correlated with higher expression levels of both defense and ethylene biosynthesis genes, as well as the ribosomal stress marker SlNAC082. In addition, Northern blotting revealed compromised ribosome biogenesis in all CEVd infected plants, particularly in Nr mutants. Our results indicate a higher ethylene biosynthesis in Nr mutants and suggest an important role of this phytohormone in disease development and ribosomal stress caused by viroid infection. Vázquez Prol, F.; López-Gresa, MP.; Rodrigo Bravo, I.; Belles Albert, JM.; Lisón, P. (2020). Ethylene is Involved in Symptom Development and Ribosomal Stress of Tomato Plants upon Citrus Exocortis Viroid Infection. Plants. 9(5):1-15. https://doi.org/10.3390/plants9050582 Flores, 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.43.040204.140243 Adkar‐Purushothama, C. R., & Perreault, J. (2019). Current overview on viroid–host interactions. WIREs RNA, 11(2). doi:10.1002/wrna.1570 Di Serio, F., Flores, R., Verhoeven, J. T. J., Li, S.-F., Pallás, V., Randles, J. W., … Owens, R. A. (2014). Current status of viroid taxonomy. Archives of Virology, 159(12), 3467-3478. doi:10.1007/s00705-014-2200-6 Verhoeven, J. th. j., Jansen, C. C. C., Willemen, T. M., Kox, L. F. F., Owens, R. A., & Roenhorst, J. W. (2004). Natural infections of tomato by Citrus exocortis viroid, Columnea latent viroid, Potato spindle tuber viroid and Tomato chlorotic dwarf viroid. European Journal of Plant Pathology, 110(8), 823-831. doi:10.1007/s10658-004-2493-5 López-Gresa, M. P., Lisón, P., Yenush, L., Conejero, V., Rodrigo, I., & Bellés, J. M. (2016). Sa