Full sequence of the coat protein gene is required for the induction of pathogen-derived resistance against sugarcane mosaic virus in transgenic sugarcane.

Sugarcane mosaic virus (SCMV) is a plant pathogenic virus of the family Potyviridae that causes chlorosis, stunting and significantly reduced sugar productivity in sugarcane. Pathogen-derived resistance is a method used to develop SCMV-resistant sugarcane by overexpression of viral DNA. In this study, the gene encoding the coat protein (CP) of SCMV was amplified by reverse transcriptase PCR from symptomatic sugarcane leaves and used to generate transgenic sugarcane. Nucleotide sequence analysis of amplified cDNA indicated that the 998-bp-long cDNA, termed ScMVCp cDNA, codes for the CP of SCMV from the PS881 isolate. The ScMVCp cDNA was inserted into the binary vector pRI101-ON with two constructs, a full nucleotide sequence (p927) and a sequence coding for N-terminally truncated protein (p702). The constructs were then introduced into sugarcane using Agrobacterium-mediated transformation. Southern blot analysis showed a single hybridized DNA copy inserted into the genome of transgenic sugarcane lines. The inserted genes were expressed at both the RNA transcript and protein levels in the transgenic sugarcane. The highest expression was found in transgenic lines 10, 11 and 13 from the p927 construct. Artificial infection by the virus showed that p927 generated a higher resistance to virus compared with p702. This resistance was passed on to the second generation of transgenic sugarcane with 100 and 20-40% levels of resistance in the p927 and p702 transgenic lines, respectively. This report shows that the full sequence of the CP gene is required to disrupt viral assembly and packaging, thereby generating resistance to SCMV infection.