Effect of Temperature on Geminivirus-Induced RNA Silencing in Plants

Abstract

Short-interfering RNAs (siRNAs), the molecular markers of posttranscriptional gene silencing (PTGS), are powerful tools that interfere with gene expression and counter virus infection both in plants and animals. Here, we report the effect of temperature on geminivirus-induced gene silencing by quantifying virus-derived siRNAs and by evaluating their distribution along the virus genome for isolates of five species of cassava geminiviruses in cassava (Manihot esculenta, Crantz) and Nicotiana benthamiana. Cassava geminivirus-induced RNA silencing increased by raising the temperature from 25°C to 30°C, with the appearance of less symptomatic newly developed leaves, irrespective of the nature of the virus. Consequently, nonrecoverytype geminiviruses behaved like recovery-type viruses under high temperature. Next, we evaluated the distribution of virusderived siRNAs on the respective virus genome at three temperatures (25°C, 25°C-30°C, and 30°C). For recovery-type viruses, siRNAs accumulated at moderately higher levels during virus-induced PTGS at higher temperatures, and there was no change in the distribution of the siRNA population along the virus genome. For nonrecovery-type viruses, siRNAs accumulated at strikingly higher levels than those observed for infections with recovery-type viruses at high temperature. As determined for an RNA virus, temperature influences gene silencing for single-stranded DNA geminiviruses. It is possible that other mechanisms besides gene silencing also control geminivirus accumulation at high temperatures. The findings presented here should be taken into consideration when implementing PTGS-based strategies to control plant virus accumulation.Posttranscriptional gene silencing (PTGS) involves sequence-specific suppression of gene expression in diverse eukaryotes. It was first discovered in plants (Napoli et al., 1990). A similar RNA-silencing phenomenon was observed in fungi, termed quelling (Cogoni and Macino, 1997), and in animals, termed RNA interference (Fire et al., 1998). In plants, PTGS serves as a natural antiviral defense response (Waterhouse et al., 2001). As a counter defense, viruses have evolved to encode a protein(s) that suppresses the host PTGS to establish infection in plants ( Vance and Vaucheret, 2001). Occasionally, certain viruses become targets of the induced PTGS, and, consequently, infected plants recover from virus infection (Ratcliff et al., 1997;Chellappan et al., 2004a). There are at least three different pathways in the gene-silencing mechanism: the cytoplasmic siRNA silencing, the endogenous mRNA silencing by microRNAs (miRNAs), and the transcriptional gene silencing by DNA methylation (Baulcombe, 2004). A unifying feature of RNA silencing is the cleavage of long double-stranded RNA (dsRNA) into short-interfering (21-24 nt) RNAs (siRNAs; Hamilton and Baulcombe, 1999) by a ribonuclease III-like enzyme termed DICER (Bernstein et al., 2001). Among the four Dicer-like (DCL) enzymes reported in plants (Schauer et al., 2002), DCL1 is involved in miRNA biogenesi...

Development and application of an efficient virus-induced gene silencing system in Nicotiana tabacum using geminivirus alphasatellite

“…It is possible that some enzymes in the pathway involved in virus-induced siRNA production might be passivated at extremely low temperatures, while some host factor(s) involved in geminivirus replication, transcription, and/or movement may be less effective at high temperature. Similar results were found previously with lower temperatures inhibiting silencing and higher temperatures eliminating virus replication (Szittya et al, 2003;Chellappan et al, 2005).…”

“…In virus-infected plants, high temperatures frequently result in attenuated symptoms and low virus accumulation (Chellappan et al, 2005). By contrast, low temperatures often induce a rapid spread of virus diseases by the control of small interfering RNA (siRNA) generation (Szittya et al, 2003).…”

Immunocapture-RT-PCR detection of Cassava common mosaic virus in cassava obtained from meristem-tip culture in Paraná state

“…Recently, it was shown that viral RNA replication of Raspberry bushy dwarf virus (RBDV), a virus that enters meristematic tissues, was disorganized in leaves and shoot tips of plants growing at a high temperature (38 o C). This was attributed to the enhancement of RNA silencing, the cellular defense mechanism of plants that acts against viral RNA (Wang et al, 2008) and is significantly more active at higher temperatures (Chellappan et al, 2005).…”

Arabidopsis DRB4, AGO1, AGO7, and RDR6 participate in a DCL4-initiated antiviral RNA silencing pathway negatively regulated by DCL1

“…It also remains to be determined whether any of the DRBs play a role in antiviral silencing. One factor that hinders the dissection of the antiviral RNA silencing machinery is that almost all plant viruses encode suppressors of RNA silencing that, depending on the growth conditions of the plants, could partially or completely disable virus-targeted RNA silencing by the plant host (6,(13)(14)(15).In this report, we implicate several more components of the plant RNA silencing machinery in antiviral defense by using mutant viruses devoid of their silencing suppressors. Specifically, we removed the silencing suppressor from our model virus, turnip crinkle virus (TCV) and used the resulting mutant viral RNAs to infect an array of Arabidopsis plants containing mutations in key silencing pathway genes.…”

“…It also remains to be determined whether any of the DRBs play a role in antiviral silencing. One factor that hinders the dissection of the antiviral RNA silencing machinery is that almost all plant viruses encode suppressors of RNA silencing that, depending on the growth conditions of the plants, could partially or completely disable virus-targeted RNA silencing by the plant host (6,(13)(14)(15).…”