Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2016
Publication Date: 2/7/2017
Citation: Li, R., Padmanabhan, C., Ling, K. 2017. A single base pair in the right terminal domain of Tomato planta macho viroid is a virulence determinant factor on tomato. Virology. 500(2017)238-246.
Interpretive Summary: Mexican papita viroid (MPVd), in genus Pospiviroid and family Pospiviroidae, first isolated from wild papita plants in 1996 has caused several disease outbreaks on greenhouse tomatoes in Canada and Mexico. The infectious clones of two MPVd isolates incited different symptoms on tomato, one isolate causing severe leaf chlorosis and plant stunting and another one inducing mild chlorosis and no plant stunting. A hybrid viroid molecule was artificially synthesized with a half of genome sequence from the severe isolate and another half from the mild isolate. This viroid-synthetic technology provided us an easy approach to study the pathogenic mechanism of a viroid.
Technical Abstract: Tomato planta macho viroid (TPMVd), including isolates previously designated as Mexican papita viroid (MPVd), causes serious disease on tomatoes in North America. Two predominant variants, sharing 93.8% sequence identity, incited distinct severe (MPVd-S) or mild (MPVd-M) symptoms on tomato. To identify virulence determinant factor, a series of chimeric infectious clones were generated using synthetic DNA approach to progressively replace each structural domain between the two variants. In bioassays on tomato ‘Rutgers’, three chimeras containing Terminal Left and Pathogenicity (MPVd-H1), Central (MPVd-H2), or Variable (MPVd-H3) of MPVd-S, incited mild to intermediate symptoms. However, a chimera containing Terminal Right (TR) of MPVd-S (MPVd-H4) incited severe symptoms. Only one base-pair mutation in the TR domain between MPVd-M (176U:A185) and MPVd-S (174G:C183) was identified. A reciprocal mutant (MPVd-H5) rendered the chimeric viroid mild on tomato. This single base-pair in the TR domain was determined as the virulence determinant factor for TPMVd.