Analysis of Pineapple Mealybug Wilt Associated Virus -1 and -2 for Potential RNA Silencing Suppressors and Pathogenicity Factors

Abstract

Higher plants use RNA silencing to defend against viral infections. As a counter defense, plant viruses have evolved proteins that suppress RNA silencing. Mealybug wilt of pineapple (MWP), an important disease of pineapple, has been associated with at least three distinct viruses, Pineapple mealybug wilt associated virus -1, -2, and -3 (PMWaV-1, -2, and -3). Selected open reading frames (ORFs) of PMWaV-1 and PMWaV-2 were screened for their local and systemic suppressor activities in Agrobacterium-mediated transient assays using green fluorescent protein (GFP) in Nicotiana benthamiana. Results indicate that PMWaV-2 utilizes a multiple-component RNA silencing suppression mechanism. Two proteins, p20 and CP, target both local and systemic silencing in N. benthamiana, while the p22 and CPd proteins target only systemic silencing. In the related virus PMWaV-1, we found that only one of the encoded proteins, p61, had only systemic suppressor activity. Of all the proteins tested from both viruses, only the PMWaV-2 p20 protein suppressed local silencing induced by double-stranded RNA (dsRNA), but only when low levels of inducing dsRNA were used. None of the proteins analyzed could interfere with the short distance spread of silencing. We examined the mechanism of systemic suppression activity by investigating the effect of PMWaV-2-encoded p20 and CP proteins on secondary siRNAs. Our results suggest that the PMWaV-2 p20 and CP proteins block the systemic silencing signal by repressing production of secondary siRNAs. We also demonstrate that the PMWaV-2 p20 and p22 proteins enhanced the pathogenicity of Potato virus X in N. benthamiana.

Perception of Mealybug Wilt Effect and Management among Pineapple Farmers in Ghana

“…The majority (88.9%) of the growers of the Queen Victoria said they were losing between 21-40% of their yield whilst 11.1% were losing 1-20% of their fruits. These findings support the reports of Dey et al (2015) which state that MWP is a major constraint on the global production of pineapple. These results also confirm MD2 as resistant pineapple variety to MWP and Smooth Cayenne as the most susceptible variety as reported by PIP (2011).…”

“…For respondents who export their produce, 31.3% of them said they were losing between 1-1000 Ghana cedis (US$ 0.244 -243), followed by 27.3% who said they were losing above 3000 Ghana cedis (above us$732), and 16.3% who were losing between 1001 and 2000 Ghana cedis (US$ 244-488), whilst 7% said they were losing between 2001 and 3000 Ghana cedis (US$ 488-732) in revenue due to the MWP disease. This results shows that the MWP disease has huge negative effect on the income on farmer income (Dey et al, 2015). Table 8 shows the disease and pest management practices adopted by the respondents.…”

Mealybug Wilt of Pineapple and Associated Viruses

“…It was therefore not surprising when multiple suppressors (two local suppressors, CP and p20, and three systemic suppressors, CPd, CP, p22, and p20) were identified in the genome of PMWaV-2 (Figure 7), suggesting that a similar multi-component silencing suppression strategy might be employed by this virus in this pathosystem [80]. Further analyses of the local suppressors have identified p20 and p22 of PMWaV-2 to be determinants of pathogenicity factors or virulence factors.…”

“…Many viral encoded proteins that were initially identified as determinants of pathogenicity or virulence factors were later identified as suppressors of RNA silencing [81,82]. In comparison, screening the PMWaV-1 genome showed only one protein, p61, with systemic silencing-suppressor activity [80] (Figure 7). activity, further supports our hypothesis that viruses encoding only weak systemic silencing suppressors might be favored in persistent infections that do not lead to plant death.…”

“…By systematically knocking out targeted viral genes, it would make it possible to reveal their functions in the host plant. To confirm the involvement of the identified suppressors and pathogenicity factors in MWP, development of an infectious clone of PMWaV-2 has been initiated [80,83]. This research might eventually pin-point the role of PMWaV in the complex etiology of MWP.…”