Presence of polyadenylated 3' tail in RNA of Pepper mild mottle virus allows the Oligo(dT)18 in Priming cDNA Synthesis of its genomic RNA template

The PCR amplification of majority of the ssRNA of both genomic and non-genomic mRNA is accomplished by RT-PCR. The mRNA is subjected to cDNA synthesis using reverse transcriptase and either Oligo(dT)18, or random or gene specific reverse primers based priming strategies. The choice of primer largely depends on the nature of 3 prime terminus of mRNA and length of cDNA synthesized. In general, oligo(dT)18 is the preferred choice for mRNAs having poly(A) tail at 3 prime terminus. In general, tobamoviruses lack any poly(A) tail at their 3 prime untranslated region (UTR) which forms a tRNA like structure and upstream pseudoknot domain except tow viruses viz., Hibiscus latent Fort Pierce virus (HLFPV) and Hibiscus latent Singapore virus (HLSV) which accommodate internal poly(A) sequences of 46 and 87 nucleotides long, respectively in their 3 prime UTR. However, determination of full nucleotide sequence of Pepper mild mottle virus (PMMoV) using an oligo(dT)18 primed cDNA as template indicated the libertinism of oligo(dT)18 in priming cDNA synthesis of RNA template which are known to lack poly(A) tail. at the end or internally at its 3 prime end. Moreover, coat protein (CP) gene of PMMoV and bean common mosaic virus (BCMV) (Potyvirus with a poly(A) tract at its 3 prime end) was amplified using cDNA primed with random primer as well as oligo(dT)18 was successfully amplified but with significant variation in the intensity of the amplification band in case of PMMoV but not in BCMV. This clearly indicated the presence of PMMoV mRNA with polyadenylated 3 prime tail in total RNA isolated from PMMoV infected capsicum leaves with abundance of non-polyadenylated PMMoV genomic RNA (gRNA). Hence, we hypothesize that the generation of polyadenylated RNA population during the infection cycle of PMMoV in pepper may be possible reason for libertinism of oligo(dT)18 in priming cDNA synthesis of RNA template isolated from PMMoV infected leaves followed by amplification of entire PMMoV genome through RT-PCR. This is first study indicating the presence of polyadenylated or polyadenylated rich regions in PMMoV gRNA acquired during the infection cycle in pepper.