Polerovirus ORF0 genes induce a host-specific response resembling viral infection

Abstract

Constitutive expression of the ORF0 (open reading frame 0) gene product from the Potato leafroll virus (PLRV) in transgenic host potato plants is known to produce viral-disease-like symptoms. To determine whether these symptoms were the result of a host-specific response to transgene expression, PLRV ORF0 and the orthologous-ORF0 genes of the closely related poleroviruses Beet western yellows virus (BWYV) and Cucurbit aphid-borne yellows virus (CABYV) were stably transformed into Solanum tuberosum and Nicotiana benthamiana plants. Only potato plants expressing the PLRV ORF0 displayed symptoms typical of virus infection, indicating a host-specific response of potato to the ORF0 gene product of the naturally infecting virus PLRV. Nicotiana benthamiana plants transgenic for PLRV ORF0 were phenotypically indistinguishable from pBIN19-transgenic and nontransformed plants, and symptom development was not obtained with potato or tobacco plants transgenic for ORF0 from BWYV or CABYV. Symptom development in potato plants transgenic for PLRV ORF0 coincided with an abnormal sugar metabolism resulting in an unusually high accumulation of starch in mesophyll cells. Tissue-specific expression of ORF0 in potato tubers resulted in abnormal tuber formation, reduced dormancy, and increased starch accumulation.