Jiayue Ji, Chendong Yue, Zengli Hu, Bingnan Chen, Longlong Zhao
B. bassiana exhibited significantly higher virulence against summer-form nymphs than winter-form nymphs across all concentrations; at the highest concentration, only 8% of summer-form survived to day 5, compared with approximately 40% survival in winter-form, representing an approximately 79-fold difference in LC50 between the two morphs. Transcriptome analysis revealed that winter-form nymphs triggered a much broader transcriptional response with 1,673 differentially expressed genes (1,344 upregulated), accompanied by coordinated induction of immune genes including phenoloxidase, lysozyme and catalase, alongside full activation of energy metabolism pathways such as oxidative phosphorylation and the TCA cycle. In contrast, summer-form nymphs showed weak immune and metabolic activation. qRT-PCR and enzyme activity assays further verified that key immune-related transcripts and enzyme activities were markedly more induced in winter-form nymphs.
INTRODUCTION: The pear psylla Cacopsylla chinensis is a destructive pear pest whose nymphs exhibit seasonal polymorphism between summer-form and winter-form morphs. Whether the two morphs differ in susceptibility to Beauveria bassiana and the underlying mechanisms have not been characterized.
METHODS: Bioassays at three spore concentrations (2.5×106, 2.5×107, and 2.5×108 spores/mL) were conducted to compare fungal virulence against fourth-instar nymphs of both morphs. Hemocyte counts and transcriptome sequencing were performed at 24 h and 36 h post-infection, respectively. qRT-PCR and enzymatic activity assays were used to further validate immune-related gene expression and enzyme activities.
RESULTS: B. bassiana exhibited significantly higher virulence against summer-form nymphs than winter-form nymphs across all concentrations; at the highest concentration, only 8% of summer-form survived to day 5, compared with approximately 40% survival in winter-form, representing an approximately 79-fold difference in LC50 between the two morphs. Transcriptome analysis revealed that winter-form nymphs triggered a much broader transcriptional response with 1,673 differentially expressed genes (1,344 upregulated), accompanied by coordinated induction of immune genes including phenoloxidase, lysozyme and catalase, alongside full activation of energy metabolism pathways such as oxidative phosphorylation and the TCA cycle. In contrast, summer-form nymphs showed weak immune and metabolic activation. qRT-PCR and enzyme activity assays further verified that key immune-related transcripts and enzyme activities were markedly more induced in winter-form nymphs.
DISCUSSION: These findings demonstrate that winter-form nymphs possess a more robust immune-metabolic defense network against B. bassiana, whereas summer-form nymphs are immune-suppressed and highly susceptible, revealing the molecular basis of morph-specific pathogen resistance shaped by seasonal polyphenism and providing a mechanistic basis for seasonally optimized biocontrol strategies.