Julius Kühn Institute (JKI)-Federal Research Centre for Cultivated Plants, Institute for Biological Control, Dossenheim, Germany.
J Virol. 2024 Jul 23;98(7):e0053724. doi: 10.1128/jvi.00537-24. Epub 2024 Jun 27.
Various isolates of the Cydia pomonella granulovirus (CpGV) are used as insect pest control agents against codling moth (CM, L.), a predominant pest in apple orchards. Three different types (I-III) of dominantly inherited field resistance of CM larvae to CpGV have been recently identified. In this study, transcription of virus genes in midgut cells of type II-resistant CM larvae infected with different CpGV isolates, i.e., CpGV-M and CpGV-S (both prone to type II resistance) as well as CpGV-E2 (breaking type II resistance) was determined by strand-specific RNA sequencing (RNA-Seq) at an early infection stage (72 h post infection). Based on principal component analysis of read counts and the quantitative distribution of single nucleotide polymorphisms (SNPs) in the RNA-Seq data, a bioinformatics analysis pipeline was developed for an identification of the infective agents. We report that (i) identification of infective agent is crucial, especially in infection experiments, when activation of covert virus infections is a possibility, (ii) no substantial difference between CpGV-M and CpGV-S transcription was found in type II-resistant CM larvae despite a different resistance mechanism, (iii) the transcription level of CpGV-M and CpGV-S was much lower than that of CpGV-E2, and (iv) (), () (), and () were identified as significantly downregulated genes in resistance-prone isolates CpGV-M and CpGV-S. For type II resistance of CM larvae, we conclude that CpGV-M and CpGV-S are both able to enter midgut cells, but viral transcription is significantly impaired at an early stage of infection compared to the resistance-breaking isolate CpGV-E2.
CpGV is a highly virulent pathogen of codling moth, and it has been developed into one of the most successful commercial baculovirus biocontrol agents for pome fruit production worldwide. The emergence of field resistance in codling moth to commercial CpGV products is a threat toward the sustainable use of CpGV. In recent years, different types of resistance (type I-III) were identified. For type II resistance, very little is known regarding the infection process. By studying the virus gene expression patterns of different CpGV isolates in midguts of type II-resistant codling moth larvae, we found that the type II resistance mechanism is most likely based on intracellular factors rather than a receptor component. By applying SNP mapping of the RNA-Seq data, we further emphasize the importance of identifying the infective agents in experiments when activation of a covert infection cannot be excluded.
各种卷叶蛾颗粒体病毒（CpGV）分离株被用作防治苹果园中主要害虫苹果蠹蛾（CM）的害虫防治剂。最近已经确定了 CM 幼虫对 CpGV 的三种不同类型（I-III）显性遗传田间抗性。在这项研究中，通过在早期感染阶段（感染后 72 小时）通过特异性 RNA 测序（RNA-Seq）测定了感染不同 CpGV 分离株（CpGV-M 和 CpGV-S（均易感染 II 型抗性）以及 CpGV-E2（破坏 II 型抗性）的 II 型抗性 CM 幼虫中病毒基因的转录。基于 RNA-Seq 数据中读计数的主成分分析和单核苷酸多态性（SNP）的定量分布，开发了一种生物信息学分析管道，用于鉴定感染剂。我们报告（i）鉴定感染剂至关重要，尤其是在感染实验中，当可能激活隐蔽性感染时，（ii）尽管抗性机制不同，但在 II 型抗性 CM 幼虫中未发现 CpGV-M 和 CpGV-S 的转录存在实质性差异，（iii）CpGV-M 和 CpGV-S 的转录水平远低于 CpGV-E2，以及（iv）（），（）（）和（）（）被鉴定为易感染分离株 CpGV-M 和 CpGV-S 中显著下调的基因。对于 CM 幼虫的 II 型抗性，我们得出结论，CpGV-M 和 CpGV-S 均能够进入中肠细胞，但与抗药性破坏分离株 CpGV-E2 相比，病毒转录在感染的早期阶段受到严重损害。
CpGV 是苹果蠹蛾的高度致病病原体，已被开发为全球苹果生产中最成功的商业杆状病毒生物防治剂之一。苹果蠹蛾对商业 CpGV 产品的田间抗性的出现对 CpGV 的可持续利用构成了威胁。近年来，已经确定了不同类型的抗性（I-III 型）。对于 II 型抗性，关于感染过程知之甚少。通过研究不同 CpGV 分离株在 II 型抗性 CM 幼虫中肠中的病毒基因表达模式，我们发现 II 型抗性机制很可能基于细胞内因素，而不是受体成分。通过应用 RNA-Seq 数据的 SNP 映射，我们进一步强调了在无法排除隐蔽感染激活的情况下，在感染实验中鉴定感染剂的重要性。
