Effect of temperature on RNA silencing of a negative‐stranded RNA plant virus: Citrus psorosis virus

Abstract

Citrus psorosis virus (CPsV), genus Ophiovirus, causes a bark scaling disease of citrus. CPsV virions are kinked filaments with three negative-stranded RNA molecules (vRNA) and a 48 kDa coat protein. The effect of temperature on symptom expression, virus accumulation and RNA silencing was examined in sweet orange seedlings (Citrus sinensis) graft-inoculated with three different CPsV isolates and grown in a glasshouse at 26 ⁄ 18°C or 32⁄ 26°C (day⁄ night). Most plants kept in the cooler glasshouse showed a shock reaction in the first flush with shoot necrosis, and then moderate to intense chlorotic flecking and spotting in young leaves, whereas plants incubated at 32 ⁄ 26°C did not exhibit shoot necrosis, and young leaf symptoms were milder. Virus titre estimated by ELISA and by northern and dot blot hybridization paralleled symptom intensity, with significantly higher virus accumulation in plants incubated at 26 ⁄ 18°C. The amount of CPsV-derived small RNAs (CPsV-sRNAs) slightly increased at 32 ⁄ 26°C, with the ratio of CPsV-sRNA ⁄ vRNA being higher at 32 ⁄ 26°C than at 26 ⁄ 18°C. These results suggest that (i) CPsV infection induces RNA silencing in citrus plants, (ii) symptom intensity is associated with virus accumulation, and (iii) temperature increase enhances the RNA silencing response of citrus plants and decreases virus accumulation.

Resistance to Citrus psorosis virus in transgenic sweet orange plants is triggered by coat protein–RNA silencing

“…Virus induced gene silencing mechanism (VIGS) is evidenced by the presence of specific siRNA for RNA1, RNA2, and RNA3 of CPsV in infected plants (Velázquez et al, 2010). We also observed VIGS induction through cp specific siRNA accumulation in the inoculated NTi plants (Fig.…”

Recent advances in Citrus psorosis virus

“…The amount of CPsVderived small RNAs (CPsV-sRNAs) slightly increased at 32/26°C, with the ratio of CPsV-sRNA/vRNA being higher at 32/26°C than at 26/18°C. These results suggest that CPsV infection induces RNA silencing in citrus plants, that symptom intensity is associated with virus accumulation, and temperature increase enhances the RNA silencing response of citrus plants and decreases virus accumulation [76].…”

“…The study reported that the observed CPsV resistance was due to preactivated RNA silencing rather than the siRNA accumulation levels in the ihp-CP transgenic sweet orange plants prior to virus challenge [49]. Virus induced gene silencing (VIGS) is evidenced by the presence of specific siRNA molecules for RNA1, RNA2, and RNA3 of CPsV in infected plants [76]. Reyes et al [49] observed also VIGS induction through CP specific siRNA accumulation in the inoculated plants.…”

“…It is important to state that sweet orange varieties will differ in their ability to show shock or leaf symptoms [53]. Psorosis symptom expression is affected by temperature, with cool temperatures favouring appearance of the shock reaction in the first flush after inoculation, while warm temperatures often inhibit shock and mask leaf symptoms [42,76]. Virus titre estimated by ELISA and by northern and dot blot hybridization paralleled symptom intensity, with significantly higher virus accumulation in plants incubated at 26/18°C [76].…”

Virus–Plant Interactions

“…Citrus plants infected with the ophiovirus CPsV have more severe symptoms in cooler greenhouses (16/18°C) (day/night) than in warmer greenhouses (32/26°C) (Velázquez et al, 2010), and virus titers parallel the symptom intensity. Outbreaks of virus diseases are often associated with low temperatures, while at high temperatures viral symptoms are often attenuated and plants can recover from virus infection (see Chapter 14, Section III, A, 3, b, ii for heat therapy).…”