Transgenic resistance by N gene of a Peanut bud necrosis virus isolate of characteristic phylogeny

Abstract

The nucleocapsid protein (N) gene of a Tospovirus devastating tomato crop in the south Indian state of Tamil Nadu was cloned and characterized. The high identity of the cloned sequence to a Peanut bud necrosis virus (PBNV) tomato isolate (97.8/99.6% nucleotide/amino acid) and a PBNV peanut isolate (94.4/96.3% nucleotide/amino acid) identified the Tospovirus as an isolate of PBNV, designated PBNV Coimbatore tomato (PBNV CT) isolate. Phylogenetic analysis of PBNV CT N gene provided useful insights into the movement and evolution of PBNV within Indian Territory. The characteristic phylogeny of PBNV CT N gene implied its potential to be an efficient transgene to confer effective PBNV resistance on crop plants. The efficacy of PBNV CT N gene in conferring PBNV resistance was studied by generating tobacco (Nicotiana tabacum L. cv Wisconsin) lines transgenic to the sense or antisense version of the gene. Several transgenic lines showed transgenic mRNA and/or protein accumulation, ranging from very high to undetectable levels, accompanied by different degrees of PBNV resistance. The undetectable or very low levels of transgene transcripts in certain PBNV-resistant sense or antisense N gene transgenic lines suggested RNA-mediated resistance by post-transcriptional gene silencing (PTGS) mechanism. However, PBNV resistance of certain transgenic lines with high levels of N gene transcripts was suggestive of possible operation of RNA-mediated non-PTGS mechanism(s) of resistance in those lines. Moreover, the high levels of N protein in certain PBNV-resistant sense N gene transgenic lines suggested protein-mediated resistance. The results predict the potential of PBNV CT N gene to confer effective PBNV resistance on tomato and other economically important crops.