Hily Jean-Michel, Scorza Ralph, Webb Kevin, Ravelonandro Michel
USDA-ARS Appalachian Fruit Research Station, 2217 Wiltshire Rd, Kearneysville, WV 25430, USA.
Mol Plant Microbe Interact. 2005 Aug;18(8):794-9. doi: 10.1094/MPMI-18-0794.
We investigated the hallmarks of posttranscription gene silencing (PTGS) in mature plants, embryos, and seedlings of the transgenic plum trees (Prunus sp.) that are resistant to Plum pox virus (PPV). We previously demonstrated that the transgene insert and resistance to PPV were mutually inherited in progeny of line C5. We show here that C5 constitutively produces a short (22 nt) and a long (25 to 26 nt) species of short interfering (si)RNA from embryo to mature plant in the absence of PPV inoculation. Unlike siRNA, methylation and transcription of the PPV-coat protein transgene were 're-set' following seed germination. Uninoculated transgenic susceptible clones did not display DNA methylation, nor did they produce detectable levels of siRNA. Upon infection, susceptible clones, transgenic or untransformed, did produce siRNA but only the short 22-nt species. These findings show that plum trees respond to virus infection by initiating PTGS-like mechanisms that involve the production of siRNA. We further suggest that high-level virus resistance in transgenic Prunus species requires the production of the long-size class of siRNA. The research adds new insights into PTGS silencing in woody perennial plant species.
我们研究了对李痘病毒（PPV）具有抗性的转基因李树（李属）成熟植株、胚胎和幼苗中转录后基因沉默（PTGS）的特征。我们之前证明，转基因插入片段与对PPV的抗性在C5系的后代中是相互遗传的。我们在此表明，在未接种PPV的情况下，C5从胚胎到成熟植株都组成性地产生短（22 nt）和长（25至26 nt）两种小干扰（si）RNA。与siRNA不同，PPV外壳蛋白转基因的甲基化和转录在种子萌发后被“重置”。未接种的转基因敏感克隆既不显示DNA甲基化，也不产生可检测水平的siRNA。感染后，敏感克隆，无论是转基因的还是未转化的，确实产生了siRNA，但只有短的22 nt种类。这些发现表明，李树通过启动涉及siRNA产生的类似PTGS的机制来应对病毒感染。我们进一步表明，转基因李属物种中的高水平病毒抗性需要产生长链类siRNA。该研究为木本多年生植物物种中的PTGS沉默提供了新的见解。
