Submitted to: Plant Cell Reports
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/3/2007
Publication Date: 9/20/2007
Citation: Lee, R.F., Febres, V.J., Moore, G.A. 2008. Transgenic Resistance to Citrus tristeza virus in Grapefruit. Plant Cell Reports, 27: 93-104 Interpretive Summary: Following the introduction of Toxoptera citricida, the brown citrus aphid and most efficient aphid vector of Citrus tristeza virus (CTV) into Florida in 1995, a team effort has been underway to develop transgenic resistance to CTV in Citrus, using grapefruit as a model system. We report here the results of long term greenhouse evaluations of 34 transgenic lines containing various constructs containing CTV genes. Most transgenic lines were susceptible to CTV, some (6 lines) were partially resistant, and one line, transformed with a construct containing the 3’ end of CTV, was resistant. The resistant line expressed the characteristics typical of transcriptional gene silencing. The results of this evaluation of transgenic lines should be useful for future research on development of transgenic resistance to CTV and other citrus viruses/pests.
Technical Abstract: Grapefruit (Citrus paradisi) transgenic plants transformed with a variety of constructs derived from the Citrus tristeza virus (CTV) genome were tested for their resistance to the virus. Most transgenic lines were susceptible (27 lines), a few were partially resistant (6 lines) and only one line, transformed with the 3’end of CTV was resistant. Transgene expression levels and siRNA accumulation were determined to identify if the resistance observed was RNA-mediated. The responses were varied. At least one resistant plant from a partially resistant line showed no steady state transgene mRNA, siRNA accumulation and no viral RNA, implicating posttranscriptional gene silencing (PTGS) as the mechanism of resistance. The most resistant line showed no transgene mRNA accumulation and promoter methylation of cytosines in all contexts, the hallmark of RNA-directed DNA methylation and transcriptional gene silencing (TGS). The variety of responses, even among clonally propagated plants, is unexplained but is not unique in perennial species. The genetics of CTV, longevity of the interaction or other factors may be responsible for this variability.