Identification of host factors involved in symptom development of BCTV

Viruses represent a unique class of pathogenic agents because of the extremely intimate associations formed between the virus and its host. Although the specific interactions of viruses with hosts can vary widely, the requirement for host factors is ubiquitous in all these interactions. In plant systems, host factors play critical roles throughout the entire virus life cycle, including the expression of viral genes, viral genome replication and viral movement. The C4 open reading frame (ORF) of Beet Curly Top Virus (BCTV) virus is necessary for symptoms typically seen during infection of Arabidopsis thaliana including swelling of bolts, abnormal floral organs, stunting, leaf curling and the formation of callus like structures. The symptoms observed suggest C4 is a plant oncogene that disrupts the cell cycle and cell fate. A two-hybrid approach identified three cDNAs: YC55 (a plant E2 homologue); YC79 (a cDNA with no known homologue in the database); and a third clone YC58 (homologue of Drosophila shaggy (sgg) and mammalian GSK3 glycogen synthase kinase). GSK3/shaggy kinase is a downstream component of the WNT/wng signaling pathway involved in patterning, cell fate determination and cytokinesis in animals. The Arabidopsis shaggy kinases are a multigene family in Arabidopsis. A second allele of the Arabidopsis shaggy kinases, MSU EST 131N6T7 (ATSK Etha) was found not to interact with C4 ORF. Promotor GUS constructs were generated to identify the developmental patterns and tissue specificity of ATSK Tetha and ATSK Etha. In this study C4 mutants were generated based on conserved amino acids among three isolates of BCTV: CFH, Logan and Worland, with a focus on serine and threonine. Two mutants (pro48 and pro48 B) were identified that impact C4 binding to ATSK Tetha and demonstrate altered phenotypes in BCTV infections. These results establish the significance of C4- ATSK Tetha binding in BCTV viral symptom development. Future work will focus on further characterizing the role of ATSK Tetha in vascular development and BCTV viral infection. Little is known about the signaling pathway that leads to the differentiation of plant vascular tissue. Identifying these components may lead to a better understanding of plant signaling in development and the differences between the regulation of the cambial meristem in woody and nonwoody dicotyledonous plants.