What is it about?

Viroids are small non-coding RNAs that can systemically infect plants. While viroids do not encode proteins, viroid RNAs interact with host proteins that mediate viroid RNA replication, transit between cells, and entry into the vascular system. These interactions result in multiplication and spread of viroid RNAs throughout the plant. In contrast, plant RNA viruses encode replication proteins, capsid proteins, and movement proteins to mediate their multiplication and spread. Co-infections of viroids and viruses are common, but interactions between viroids and viruses are not well understood. In this study, Potato spindle tuber viroid (PSTVd) and PSTVd mutants unable to move between specific cell types were used to investigate whether Tobacco mosaic virus (TMV) movement protein (MP) can facilitate PSTVd spread. We found that TMV MP was able to mediate the movement of PSTVd mutants defective for spread between some cell types, but not others. Specifically, TMV MP could complement PSTVd mutants unable to spread between certain leaf cell types, but not cell types necessary for vascular entry. This suggests that RNA trafficking mechanisms differ between different cell types, and that TMV MP can productively interact with PSTVd RNA to allow it's passage between some but not all barriers. The results also demonstrate a novel strategy for functional analysis of MPs.

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Why is it important?

Understanding how plant viruses and viroids spread between cells is important because these pathogens can cause significant damage to crops, leading to reduced yields and economic losses for farmers. For example, Hop latent viroid (HLVd) was recently identified as a significant pathogen of cannabis, and PSTVd is a serious pathogen of potato and tomato. In addition, plant viruses and viroids are able to spread systemically throughout the entire plant, making them difficult to control once an infection has been established. By studying mechanisms of viral and viroid spread in plants, it may be possible to identify new cellular targets for developing strategies to prevent or control these diseases. This could include engineering crops with improved resistance to viral and viroid infections. Furthermore, since co-infections of viruses and viroids often occur in plants, understanding their interactions could provide insights into the broader mechanisms of plant-pathogen interactions and the evolution of plant pathogens.


The findings of this study have several implications for future research. First, further investigations into interactions between viroids and viruses in plant cells could help to better understand the mechanisms that underlie their spread. Additionally, this study highlights the potential for using wild type and mutant viroids as tools to probe the functions of viral proteins, which could provide new insights into the mechanisms of viral infection and spread. Further, the identification of different mechanisms for viral and viroid spread between different cell types could lead to development of more targeted and effective strategies for controlling these pathogens. Finally, the insights gained from future studies of this type could have broader implications for the understanding of plant-pathogen interactions and the evolution of plant pathogens, which will ultimately contribute to the development of more sustainable and resilient agricultural practices.

Jian Wu
Ningbo University

Read the Original

This page is a summary of: Tobacco mosaic virus movement protein complements a Potato spindle tuber viroid RNA mutant impaired for mesophyll entry but not mutants unable to enter the phloem, PLoS Pathogens, December 2022, PLOS, DOI: 10.1371/journal.ppat.1011062.
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