Plant viruses cause significant losses in food, fiber and forage crops throughout the world. The ability of plant viruses to cause these diseases is often linked to their ability to move systemically throughout their hosts. Systemic movement generally requires the virus to gain access to the plant's vascular phloem. As the plant's main transport tissue, phloem functions in the systemic movement of a diverse set of molecules. The movement of these molecules has a vital role in mediating plant metabolism, development and pathogen defenses, including age related resistance. Thus, to be successful viruses must overcome these defenses in order to usurp this transport tissue. Unfortunately, mechanisms controlling this form of resistance are not well studied. Efforts in this project will investigate the regulation and role of ARR in preventing virus systemic movement through the vascular phloem using a model virus - plant pathosystem. Additional studies will determine the mechanisms viruses use to overcome this resistance and achieve systemic spread throughout the plant. Since age-related resistance impacts a wide range of pathogen-host systems, it is anticipated that this study will have broad implications to many agriculturally important crops. Additional broader impacts will involve the integration of virology and plant biology disciplines for the training of graduate, undergraduate and high school students with the goal of introducing these students to the diverse career opportunities available in these fields.
Technical Paragraph
Using a tobacco mosaic virus (TMV) - Arabidopsis system, efforts in this proposal will exploit the ability of TMV to reprogram phloem specific transcription through an interaction with the companion cell (CC) expressed auxin indole acetic acid transcription regulator IAA26. IAA proteins are components of the plant auxin response system and play essential roles in many aspects of plant development, metabolism and defense. The ability of TMV to successfully disrupt IAA26 function significantly enhances virus systemic movement in older plant tissues. Phloem specific transcriptional studies demonstrate a role for IAA26 in the regulation of salicylic and jasmonic acid defense responses that are associated with age related resistance (ARR). Thus, TMV reprograming of IAA26 directed gene regulation likely functions in the suppression of ARR. The identification of this interaction represents a novel system from which to investigate molecular mechanisms involved in virus phloem loading. Efforts in this proposal will focus on identifying the CC expressed ARF transcription factors modulated by IAA26, identify CC genes under the control of IAA26 regulation and characterize the impact of IAA26 regulated CC genes on virus phloem loading. Combined these studies will have broad impacts on our understanding of phloem-mediated virus movement that could result in new strategies to control these agriculturally important pathogens. Additional broader impacts will introduce high school and undergraduate students to the diverse research opportunities available in the fields of plant biology, virology and biotechnology with the goal of encouraging these students to consider advanced training in these areas.
