Triticum mosaic virus (TriMV; genus Poacevirus; family Potyviridae) is an economically important virus in the Great Plains region of the USA. TriMV is transmitted by wheat curl mite (Aceria tosichella Keifer) Type 2 genotype but not by Type 1. HC-Pro is a vector transmission determinant for several potyvirids, but the role of HC-Pro in TriMV transmission is unknown. In this study, we examined the requirement of HC-Pro cistron of TriMV for wheat curl mite (Type 2) transmission through deletion and point mutations and constructing TriMV chimeras with heterologous HC-Pros from other potyvirids. TriMV with complete deletion of HC-Pro failed to be transmitted by wheat curl mites at detectable levels. Furthermore, TriMV chimeras with heterologous HC-Pros from aphid-transmitted turnip mosaic virus and tobacco etch virus, or wheat curl mite-transmitted wheat streak mosaic virus, failed to be transmitted by wheat curl mites. These data suggest that heterologous HC-Pros did not complement TriMV for wheat curl mite transmission. A decreasing series of progressive nested in-frame deletions at the N-terminal region of HC-Pro comprising amino acids 3-125, 3-50, 3-25, 3-15, 3-8, and 3 and 4 abolished TriMV transmission by wheat curl mites. Additionally, mutation of conserved His20, Cys49, or Cys52 to Ala in HC-Pro abolished TriMV transmissibility by wheat curl mites. These data suggest that the N-terminal region of HC-Pro is crucial for TriMV transmission by wheat curl mites. Collectively, these data demonstrate that the HC-Pro cistron of TriMV is a viral determinant for wheat curl mite transmission.
Keywords: Virology.