Citrus exocortis viroid (CEVd) and citrus bark cracking viroid (CBCVd) are two important viroids that infect citrus plants and frequently occur as mixed infections in orchards. However, the mechanism of antagonism between the two viroids in mixed infections remains unclear. The CEVd/CBCVd–citron system and small RNA sequencing (sRNA-seq) were used to study the antagonism. When CBCVd was inoculated before CEVd, the CEVd titre was significantly reduced and the symptoms were attenuated. Viroid-derived sRNAs (vd-sRNAs) from CEVd and CBCVd were predominantly 21-nucleotide (nt) and 22-nt in length and had similar 5′ base biases. Homologous sequences of the two viroids in the terminal right (TR) region are rich in vd-sRNAs, and the high frequency vd-sRNAs selected from the CBCVd TR region can be used to degrade the transcripts of CEVd in vivo directly. These results suggest that RNA silencing may play an important role in the antagonism of the two viroids, thus deepening our understanding of the molecular interaction of long noncoding RNAs in woody plants.

中文翻译：

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RNA沉默对柑橘外皮类病毒和柑橘皮裂类病毒拮抗作用的影响

柑橘外皮质类病毒（CEVd）和柑橘皮裂类病毒（CBCVd）是感染柑橘植物的两种重要类病毒，在果园中经常以混合感染的形式发生。然而，两种类病毒在混合感染中的拮抗机制仍不清楚。CEVd/CBCVd-citron 系统和小 RNA 测序 (sRNA-seq) 用于研究拮抗作用。当在CEVd之前接种CBCVd时，CEVd滴度显着降低并且症状减轻。来自 CEVd 和 CBCVd 的类病毒衍生 sRNA (vd-sRNA) 主要长度为 21 核苷酸 (nt) 和 22 nt，并且具有相似的 5' 碱基偏倚。两种类病毒的末端右端(TR)区的同源序列富含vd-sRNA，从CBCVd TR区中筛选出的高频vd-sRNA可用于在体内直接降解CEVd的转录本。这些结果表明RNA沉默可能在两种类病毒的拮抗作用中发挥重要作用，从而加深我们对木本植物中长链非编码RNA分子相互作用的理解。