Suppression of bamboo mosaic virus accumulation by a putative methyltransferase in Nicotiana benthamiana.
Bamboo mosaic virus (BaMV) is a 6.4-kb positive-sense RNA virus belonging to the genus Potexvirus of the family Flexiviridae. The 155-kDa viral replicase, the product of ORF1, comprises an N-terminal S-adenosyl-l-methionine (AdoMet)-dependent guanylyltransferase, a nucleoside triphosphatase/RNA 5'-triphosphatase, and a C-terminal RNA-dependent RNA polymerase (RdRp). To search for cellular factors potentially involved in the regulation of replication and/or transcription of BaMV, the viral RdRp domain was targeted as bait to screen against a leaf cDNA library of Nicotiana benthamiana using a yeast two-hybrid system. A putative methyltransferase (PNbMTS1) of 617 amino acid residues without an established physiological function was identified. Cotransfection of N. benthamiana protoplasts with a BaMV infectious clone and the PNbMTS1-expressing plasmid showed a PNbMTS1 dosage-dependent inhibitory effect on the accumulation of BaMV coat protein. Deletion of the N-terminal 36 amino acids, deletion of a predicted signal peptide or transmembrane segment, or mutations in the putative AdoMet-binding motifs of PNbMTS1 abolished the inhibitory effect. In contrast, suppression of PNbMTS1 by virus-induced gene silencing in N. benthamiana increased accumulation of the viral coat protein as well as the viral genomic RNA. Collectively, PNbMTS1 may function as an innate defense protein against the accumulation of BaMV through an uncharacterized mechanism.
Cheng
Chun-Wei
CW
Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan.
Hsiao
Yi-Yuong
YY
Wu
Hui-Chuan
HC
Chuang
Chi-Mau
CM
Chen
Jao-Shien
JS
Tsai
Ching-Hsiu
CH
Hsu
Yau-Heiu
YH
Wu
Yao-Chu
YC
Lee
Cheng-Cheng
CC
Meng
Menghsiao
M
D000595:Amino Acid Sequence; D008780:Methyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D017863:Potexvirus / Q000201:enzymology* / Q000235:genetics; D011485:Protein Binding; D011523:Protoplasts / Q000378:metabolism; D013379:Substrate Specificity; D014026:Nicotiana / Q000821:virology*; D020798:Two-Hybrid System Techniques
D008780:Methyltransferases