Understanding the role of virus-host interactions in tissue tropism of plant viruses

C.E. Credits: P.A.C.E. CE Florida CE
Speaker
  • Associate Professor, Department of Plant Pathology, Plant Molecular and Cellular Biology Program, University of Florida
    Biography

      Dr. Svetlana Y. Folimonova received her PhD in Microbiology from Moscow State University, Moscow, Russia. She held a postdoctoral position at the S. R. Noble Foundation, Ardmore, Oklahoma and a postdoctoral position at the University of Florida, Citrus Research and Education Center, Lake Alfred, Florida. Dr. Folimonova was appointed Assistant Professor of Plant Pathology at the University of Florida, Gainesville, Florida, in 2012. In 2016, she was promoted to Associate Professor. Dr. Folimonova's research program focuses on viral and bacterial pathogens of citrus, with the main emphasis on Citrus tristeza virus (CTV) and Candidatus Liberibacter asiaticus, a causal agent of citrus greening [Huanglongbing (HLB)]. Her primary research effort is concentrated on understanding the mechanisms of the infection process, host responses to the pathogens, improving methods of detection, and developing management strategies for these diseases. In 2020, Dr. Folimonova received a prestigious Syngenta Crop Protection Award from the American Phytopathological Society for her outstanding contributions to research on CTV and, specifically, for the elucidation of the mechanism of the CTV superinfection exclusion and for the research accomplishments on the development of the CTV-based vectors for expression of antimicrobial proteins for management of citrus greening. Dr. Folimonova also serves as Councilor for Plant Virology at the American Society for Virology.


    Abstract

    To establish productive infection, plant viruses need to be able to efficiently invade and spread within a plant. Most viruses are introduced into a plant via the epidermal or mesophyll cells where they undergo disassembly, replication, translation of their proteins, and assemble new virions. Viruses then move to the adjacent cells until they reach the phloem, which serves as the highway by which viruses spread throughout their hosts. It was shown that the phloem has evolved additional protection against these molecular intruders. Virus entry into, translocation through, and exit from the phloem involve additional viral factors and complex virus-host interactions. Although the majority of plant viruses are capable of infecting most types of cells within their hosts, there are several groups of plant viruses whose tissue tropism is limited to the phloem. These viruses are typically introduced directly into the phloem by vectoring phloem-feeding insects. Interestingly, the movement systems of such viruses are complex and involve multiple viral proteins. The factors and processes that control phloem restriction of these viruses are not well understood. We are working with Citrus tristeza virus (CTV), the largest non-segmented positive-sense RNA virus of plants, which belongs to the family Closteroviridae. In our recent study, we showed that the p33 protein of CTV is a viral effector, which affects viral pathogenicity by modulating a host immune response. Upon CTV infection, p33 triggers the accumulation of reactive oxygen species (ROS) and plant cell death. Deletion of the p33 gene from the CTV genome resulted in a significant decrease in the ROS production during virus invasion of the host plants and an increase in the virus accumulation and spread.  Remarkably, the p33 deletion mutant was able to spread beyond the phloem and enter the immature xylem cells where it perturbed the vascular tissue differentiation leading to the enhancement of the stem pitting syndrome. We hypothesize that the plant recognizes p33 and activates the host immune response to restrict CTV into the phloem tissue and minimize the disease.

    Learning Objectives:

    1. Learn how plant viruses move cell-to-cell and long-distance in their hosts

    2. Understand how plant viruses modulate phloem to their advantage

    3. Get familiar with mechanisms plants have developed to perceive and defeat viruses

    4. Learn what factors mediate phloem restriction of certain plant viruses.


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