Hibiscus chlorotic ringspot virus coat protein inhibits trans-acting small interfering RNA biogenesis in Arabidopsis

Abstract

Many plant and animal viruses have evolved suppressor proteins to block host RNA silencing at various stages of the RNA silencing pathways. Hibiscus chlorotic ringspot virus (HCRSV) coat protein (CP) is capable of suppressing the transiently expressed sense-RNA-induced posttranscriptional gene silencing (PTGS) in Nicotiana benthamiana. Here, constitutively expressed HCRSV CP from transgenic Arabidopsis was found to be able to rescue expression of the silenced GUS transgene. The HCRSV CP-transgenic Arabidopsis (line CP6) displayed several developmental abnormalities: elongated, downwardly curled leaves and a lack of coordination between stamen and carpel, resulting in reduced seed set. These abnormalities are similar to those observed in mutations of the genes of Arabidopsis RNA-dependent polymerase 6 (rdr6), suppressor of gene silencing 3 (sgs3), ZIPPY (zip) and dicer-like 4 (dcl4). The accumulation of microRNA (miRNA) miR173 remained stable; however, the downstream trans-acting small interfering RNA (ta-siRNA) siR255 was greatly reduced. Real-time PCR analysis showed that expression of the ta-siRNA-targeted At4g29770, At5g18040, PPR and ARF3 genes increased significantly, especially in the inflorescences. Genetic crossing of CP6 with an amplicon-silenced line (containing a potato virus X-green fluorescent protein transgene under the control of the 35S cauliflower mosaic virus promoter) suggested that HCRSV CP probably interfered with gene silencing at a step after RDR6. The reduced accumulation of ta-siRNA might result from the interference of HCRSV CP with Dicer-like protein(s), responsible for the generation of dsRNA in ta-siRNA biogenesis. INTRODUCTIONSmall-RNA-mediated silencing pathways play important roles in a variety of processes, including defence against viruses. Viruses in turn evolve mechanisms to interfere with the host silencing responses for successful infection, which usually results in differential developmental defects. The molecular basis of gene-silencing-related abnormal development is mediated by a group of small RNAs, including microRNAs (miRNAs) and small interfering RNAs (siRNAs) (Bartel, 2004;Baulcombe, 2004; JonesRhoades et al., 2006). The miRNAs are a class of small RNAs similar to siRNAs that are key components of the complex networks of gene regulatory pathways. As most plant miRNAs contain near-perfect complementarities with target sequences, they are thought to function like siRNAs in guiding target RNA for cleavage (Rhoades et al., 2002). In Arabidopsis thaliana, there are four Dicer-like proteins (DCLs) that are responsible for the production of miRNAs and siRNAs of different sizes. All four DCLs act in combination to help mediate plant responses to diverse viral infections (Blevins et al., 2006;Deleris et al., 2006).The plant miRNAs target a series of genes/gene families that are important for normal plant development (Kidner & Martienssen, 2005). Interference in miRNA biogenesis or miRNA-target interactions lead to developmental abnormalities (Bartel & Bartel, 2003;Dugas & Ba...

tasiRNA-ARF Pathway Moderates Floral Architecture inArabidopsisPlants Subjected to Drought Stress

“…155 genes coexpressed with ARF3 and ARF4 involved twenty-five abiotic stress response-related genes, such as DREB2C [44], DWD ( DDB1-binding WD40 protein ) [45], ascorbate peroxidase 1 [46], glutathione S-transferase [47], and RD21B [48] (Supplemental Table 4). Thegenes also included ta-siRNA pathway-related genes, such as RDR6 , TAS3 , other TAS genes, and ta-siRNA target genes [49]. Sixty-four of the 155 genes possessed an ARF binding motif (tgtctc) [50] in the promoter region within 1kb upstream of the start codon (Supplemental Table 4).…”

p2 of Rice stripe virus (RSV) interacts with OsSGS3 and is a silencing suppressor

“…The alteration of the ta‐siRNA pathway has been reported in many plant–virus combinations and has been suggested to be involved in symptom development (Lacombe et al ., 2010; Meng et al ., 2008; Shivaprasad et al ., 2008). In this study, we found that the ta‐siRNA pathway may be affected in RSV‐infected rice.…”

Basic Amino Acid Mutations in the Nuclear Localization Signal of Hibiscus Chlorotic Ringspot Virus p23 Inhibit Virus Long Distance Movement

“…A biologically active cDNA clone of HCRSV p223 has been obtained previously [3]. The HCRSV CP (p38) [3] is a gene silencing suppressor [12]. In addition, p27 and its other in-frame isoforms (p25 and p22.5) affect symptom expression and potentiate Carmoviruses movement in kenaf ( Hibiscus cannabinus L.) [13].…”