Transgenic resistance to Citrus tristeza virus in grapefruit.
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 whether 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 to citrus. The genetics of CTV, host response or other factors may be responsible for this variability.
Febres
Vicente J
VJ
Horticultural Sciences Department, University of Florida, PO BOX 110690, Gainesville, FL, 32611, USA. vjfebres@ifas.ufl.edu
Lee
Richard F
RF
Moore
Gloria A
GA
D001483:Base Sequence; D015139:Blotting, Southern; D032083:Citrus paradisi / Q000235:genetics* / Q000821:virology; D007113:Immunity, Innate / Q000235:genetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000235:genetics* / Q000821:virology; D010942:Plant Viruses / Q000235:genetics / Q000254:growth & development*; D030821:Plants, Genetically Modified / Q000235:genetics* / Q000821:virology; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014170:Transformation, Genetic / Q000235:genetics
D012333:RNA, Messenger; D034741:RNA, Small Interfering