Development of an Efficient Virus Induced Gene Silencing Strategy in the Non-Model Wild Ginger-Zingiber zerumbet and Investigation of Associated Proteome Changes.

Zingiber zerumbet (Zingiberaceae) is a wild, tropical medicinal herb that shows a high degree of resistance to diseases affecting cultivated ginger. Barley stripe mosaic virus (BSMV) silencing vectors containing an endogenous phytoene desaturase (PDS) gene fragment were agroinfiltrated into young leaves of Z. zerumbet under controlled growth conditions to effect virus-induced gene silencing (VIGS). Infiltrated leaves as well as newly emerged leaves and tillers showed visual signs of PDS silencing after 30 days. Replication and systemic movement of the viral vectors in silenced plants were confirmed by RT-PCR. Real-time quantitative PCR analysis verified significant down-regulation of PDS transcripts in the silenced tissues. Label-free proteomic analysis was conducted in leaves with established PDS transcript down regulation and buffer-infiltrated (mock) leaves. A total of 474 proteins were obtained, which were up-regulated, down-regulated or modulated de novo during VIGS. Most of these proteins were localized to the chloroplast, as revealed by UniprotKB analysis, and among the up-regulated proteins there were abiotic stress responsive, photosynthetic, metabolic and membrane proteins. Moreover, the demonstration of viral proteins together with host proteins proved successful viral infection. We report for the first time the establishment of a high-throughput gene functional analysis platform using BSMV-mediated VIGS in Z. zerumbet, as well as proteomic changes associated with VIGS.

Mutational analysis of the putative catalytic triad of the cowpea mosaic virus 24K protease.

To investigate the mechanism of action of the cowpea mosaic virus (CPMV) 24K protease, a full-length cDNA clone of bottom component (B) RNA has been constructed from which RNA can be transcribed in vitro using T7 RNA polymerase. Translation of the resulting RNA in rabbit reticulocyte lysate leads to the synthesis of a 200 kDa product (the 200K protein) which cleaves itself in a manner identical to that of the product translated from B RNA isolated from virions. Site-directed mutagenesis of the full-length clone was used to examine the effects of altering individual amino acids in the 24K protease on its activity. The results obtained are consistent with the prediction that the 24K protease is structurally similar to the trypsin-like family of serine proteases and suggest that His40, Glu76, and Cys166 comprise the active site. Substitution of Cys166 by a serine residue results in an enzyme with reduced catalytic activity.