CaRDR1, an RNA-Dependent RNA Polymerase Plays a Positive Role in Pepper Resistance against TMV

Abstract

RNA silencing functions as a major natural antiviral defense mechanism in plants. RNA-dependent RNA polymerases (RDRs) that catalyze the synthesis of double-stranded RNAs, are considered as a fundamental element in RNA silencing pathways. In Arabidopsis thaliana, RDR1, 2 and 6 play important roles in anti-viral RNA silencing. Expression of RDR1 can be elevated following plant treatment with defense hormones and virus infection. RDR1 has been studied in several crop species, but not in pepper (Capsicum annuum L.). Here, a RDR1 gene was isolated from Capsicum annuum L., designated as CaRDR1. The full-length cDNA of CaRDR1 was 3,351 bp, encoding a 1,116-amino acid protein, which contains conserved regions, such as the most remarkable motif DLDGD. The transcripts of CaRDR1 could be induced by salicylic acid (SA), abscisic acid (ABA), H2O2, and tobacco mosaic virus (TMV). Silencing of CaRDR1 in pepper resulted in increased susceptibility to TMV as evident by severe symptom, increased of TMV-CP transcript, higher malondialdehyde (MDA) content and lower antioxidant enzymes activities compared with that of control plants. CaRDR1-overexpressing in Nicotiana benthamiana showed mild disease symptom and reduced TMV-CP transcripts than that of empty vector (EV) following TMV inoculation. The RNA silencing related genes, including NbAGO2, NbDCL2, NbDCL3, and NbDCL4 elevated expression in overexpressed plants. Alternative oxidase (AOX), the terminal oxidase of the cyanide (CN)-resistant alternative respiratory pathway, catalyze oxygen-dependent oxidation of ubiquinol in plants. It has an important function in plant defense against TMV. In addition, CaRDR1 overexpression promoted the expression of NbAOX1a and NbAOX1b. In conclusion, these results suggest that CaRDR1 plays a positive role in TMV resistance by regulating antioxidant enzymes activities and RNA silencing-related genes expression to suppress the replication and movement of TMV.

Plant defense against virus diseases; growth hormones in highlights

“…119,120 Furthermore, ABA exogenous application increases the resistance of plants against viruses such as TMV and Tobacco necrosis virus (TNV) by hindering the virus movement. [121][122][123] Another phytohormone which is closely linked to the closure of PD is SA. Specifically, SA exogenous application results in the deposition of callose within PD.…”

RNA Interference: A Natural Immune System of Plants to Counteract Biotic Stressors

“…Recently, it was found that Tobacco mosaic virus-coat protein (TMV-CP) accumulation was less in the CaRDR1 overexpressing tobacco lines following TMV infection. Furthermore, TMV inoculation enhanced transcript levels of AGOs and DCls genes in the RDR1 expressing lines [136]. Similarly, MdRDR1 transgenic tobacco plants enhanced resistance against TMV, Sunn hemp mosaic virus and Turnip vein-clearing virus [137,138].…”

“…In the case of CMV, the siRNAs production depends on the RDR1, and these secondary vsiRNAs are important for antiviral silencing [88]. Silencing of RDR1 or knockout rdr1 mutants result in a higher level of virus RNA and reduces resistance in pepper, Arabidopsis , maize, and tomato plants [136,139,140,141], however, the resistance of potato to PVX and PVY is not compromised [142]. As we mentioned, RDR2 protein along with DCL3 is involved in the production of 24 nt siRNAs, and loss of RDR2 function causes extensive changes in the expression of genes, transposons and 24 nt sRNAs [61].…”

Genome-Wide Analysis of DCL, AGO, and RDR Gene Families in Pepper (Capsicum Annuum L.)

“…In previous study, we cloned CaRDR1 from pepper, which was induced by salicylic acid (SA) and tobacco mosaic virus (TMV). CaRDR1 played a positive role in pepper TMV resistance by regulating antioxidant enzymes’ activities and the expression of RNA silencing-related genes [ 18 ]. In this study, the expression pattern of pepper AGO , DCL and RDR gene families were examined in response to biotic/abiotic stress.…”