Differential induction and suppression of the potato innate immune system in response to Alfalfa mosaic virus infection

Abstract

Alfalfa mosaic virus (AMV) causes significant losses in the global agricultural production of crops such as potato (Solanum tuberosum L.). Transcriptional levels of 10 innate defense genes, five related to the polyphenol biosynthetic pathway (PAL, HQT, HCT, CHS, and CHI) and five pathogenesis-related proteins (PR-1, PR-2, PR-3, PR-5 and PR-7) were investigated at different days post-inoculation (dpi). The results revealed that fluctuations in the expression of these examined defense genes between induction and suppression, especially in the first 10 dpi, are common. Interestingly, greater up-regulation of most of the tested genes at 4 dpi was associated with greater down-regulation of PR-2 and a reduction in viral coat protein (CP) accumulation. Conversely, greater activation and accumulation of the virus at 10 dpi suppressed the expressions of all genes except PR-1 (salicylic marker gene), and CHI genes showed 1.189- and 1.028-fold changes respectively. At 30 dpi, the greatest level of AMV-CP accumulation (42.27-fold) was associated with severe symptoms that started appearing at 18 dpi. Consequently, at 30 dpi, none of these genes had an effect on the presence and multiplication of the virus inside the plant cell. This study provides the first valuable information of the molecular transcriptional levels of these potato genes under AMV infection.