A team of the Institute of Plant Molecular and Cellular Biology (IBMCP), a mixed centre of the Polytechnic University of Valencia and the Spanish National Research Council worked to figure out why the pathogen was present in ribosomes, and the answer they found opens a heretofore closed door to fight against the viroid. These pathogens have great infectious power, affecting plants, and are on of the main enemies of crops, especially citrus fruit trees.
From their laboratories, the scientists have described for the first time how a pathogen – in this case the viroid of citrus exocortis – can cause ribosome stress in plants, which directly affects their physiological condition. Other entities that have taken part in this study, whose conclusions have been published in journal Nucleic Acids Research, include the University of Sherbrooke (Québec, Canada) and Goethe University (Frankfurt, Germany).
“This study opens a new dimension in viroid pathogenesis. It is the first time that it has been verified that the viroid, plant pathogens, cause a malfunction in the formation of ribosomes, which are necessary to produce proteins,” explains Purificación Lisón, researcher at the IBMCP and professor of the Higher Agricultural Engineering and Natural Medium Technical School (ETSIAMN) of the UPV.
In the protein creation process, called “translation”, the ribosome is the molecular machine in charge of reading and deciphering the sequence of messenger RNA and turn it into a protein sequence. In this study, the team of Spanish, Canadian and German researchers have verified how the viroid can alter this process, and that “the greater the alteration is, the more the plant gets ill,” adds Purificación Lisón.
But, how can the viroid cause the alteration? The researchers discovered that the viroid, who are RNA sequences themselves, interfere in the shaping of ribosome RNA, a key step in the formation and assembly of ribosomes. “The pathogen could be interfering in the RNA maturation process, which would directly affect the creation of the ribosome, producing a failure in the plant’s translation machinery and, ultimately, causing the disease,” explains Ismael Rodrigo, fellow researcher at the IBMCP and professor at the UPV’s ETSIAMN.
A possible biotechnological solution to prevent this from happening could consist on competing with the interference generated by the viroid by producing additional copies of the RNA that is necessary for the ribosome RNA to be created, and which could become displaced due to the presence of the vidoid. “This way we would make it so that the viroid does not cause alterations to the appropriate maturation of ribosome RNA. It could be considered an RNA competition strategy,” adds Alejandro Ferrando, another researcher at the IBMCP – and senior scientist at the CSIC -, who took part in this project.
In the study, the research team has worked essentially with tomato plants, used as experimental hosts. “It is a plant that manifests the same disease as citric fruits, but is easier to handle,” notes Purificación Lisón.
As well as citric fruits and tomatoes, the viroid also affects other cultivated species such as potatoes, grapes, apples, peaches or avocados, among others.
The researchers are now analysing whether their finding regarding the viroid can also be the case for other plant pathogens. Furthermore, they add that their study could pave the way for research to apply their findings in human pathologies that affect ribosomes.
Patrick Cottilli, Borja Belda-Palazón, Charith Raj Adkar-Purushothama, Jean-Pierre Perreault, Enrico Schleiff, Ismael Rodrigo, Alejandro Ferrando, Purificación Lisón. Citrus exocortis viroid causes ribosomal stress in tomato plants. Nucleic Acids Research https://doi.org/10.1093/nar/gkz679