HSC70-3 in the Gut Regurgitant of Diamondback Moth, Plutella xylostella: A Candidate Effector for Host Plant Adaptation

The co-evolution between plants and herbivorous insects has led to a continuous arms race on defense and anti-defense mechanisms. In this process, insect-derived effectors are crucial for suppressing plant defense. Despite considerable progress in plant-insect interaction studies, the functional role of heat shock cognate protein 70 (HSC70) as an effector in herbivorous insects remains poorly characterized. This study provides evidence that HSC70-3 functions as an effector in interactions between the cruciferous specialist diamondback moth (<i>Plutella xylostella</i>) and its host plant radish (<i>Raphanus sativus</i> 'Nanpan Prefecture'). Using immunofluorescence labeling and in situ Western blot (WB), we demonstrated that HSC70-3 is secreted into plant wound sites through larval gut regurgitant during feeding. Short-term host transfer experiments revealed tissue-specific <i>hsc70-3</i> expression changes, indicating a dynamic response to plant-derived challenges. These findings suggest <i>hsc70-3</i> is differentially regulated at transcriptional and translational levels to facilitate insect adaptation to host plant shifts. Knockout of <i>hsc70-3</i> using CRISPR/Cas9 technology significantly impaired larval growth, prolonged development duration, and reduced pupal weight on host plants, indicating its involvement in host adaptation. However, knockout mutants exhibited no significant developmental defects when reared on an artificial diet, suggesting that <i>hsc70-3</i> primarily functions in modulating plant-induced defense responses rather than directly affecting insect physiology. Collectively, these findings provide evidence for the functional roles of HSC70-3 in <i>P. xylostella</i> and plant interactions, laying a foundation for further investigations into insect effectors and their mechanisms in modulating plant defense responses.