Molecular Characterization of a Nicotiana tabacum NtRDR6 Gene

Abstract

RNA-dependent RNA polymerases (RDRs) play key roles in RNA silencing, developmental regulation, antiviral defense and the maintenance of genome integrity. In this work, we isolated an RDR gene (NtRDR6) from Nicotiana tabacum using reverse-transcription PCR (RT-PCR) and rapid amplification of cDNA ends PCR (RACE-PCR) technology. The full-length cDNA of NtRDR6 encodes a protein of 1,197 amino acids, which contains all of the five highly conserved regions in plant RDRs and the DxDGD signature motif. An amino acid sequence alignment revealed that NtRDR6 shares a high level of similarity with other known RDRs. The genomic sequence of NtRDR6 contains two introns and a group of putative cis-acting elements in the 5′-flanking region. Expression analysis performed using 6-week-old seedlings revealed that the transcript level of NtRDR6 is up-regulated by diverse signalling molecules, including jasmonate (JA), abscisic acid (ABA), gibberellin A (GA) and salicylic acid (SA). The expression of NtRDR6 is also elevated markedly by Cucumber mosaic virus (CMV) and Potato virus X (PVX) but not by Potato virus Y (PVY) and Tobacco mosaic virus (TMV). Notably, abiotic stresses have alternative effects on the transcription of NtRDR6, with heat (37°C) significantly increasing the expression of NtRDR6, whereas low temperature (15°C) does not affect expression. These results indicated that NtRDR6 may be involved in several signal transduction pathways to defend against plant virus attack and in the response to abiotic stresses.