Haibo Bao

Rice (Oryza sativa) is a crucial staple for more than half of the global population, yet it faces significant pest pressures, notably from the striped stem borer, Chilo suppressalis. This insect deposits eggs on rice surfaces, and their hatched larvae bore into stems, causing substantial yield losses. Whereas the responses of rice to larval feeding are well-documented, less is known about its reaction to C. suppressalis oviposition at the molecular and biochemical levels, despite evidence that insect egg deposition triggers various defence mechanisms in plants. In this study, next-generation RNA sequencing and comprehensive metabolomics were utilised to analyse rice leaves with and without eggs, revealing shifts in gene expression and metabolite synthesis. The effects of egg-deposited rice to oviposition behaviour were also tested. The results indicated 1,350 differentially expressed genes and 234 differential metabolites 24 h after C. suppressalis oviposition. Up-regulated genes included those involved in defence, stress responses, and secondary metabolism. Furthermore, metabolomic studies indicated increased levels of lipids, flavonoids, terpenoids, and phenolic compounds in response to oviposition, mirroring the observed responses against pathogens. Oviposition behavioural test results suggested that C. suppressalis oviposition activity was deterred by egg-laden rice. These findings enhance our understanding of induced defence mechanisms in rice against C. suppressalis at the molecular and biochemical levels, potentially guiding the development of ovicidal substances, insect-resistant rice varieties, and rice-protection strategies.

Survival and adaptation to seasonal changes are challenging for insects. Many temperate insects such as the rice stem borer (Chilo suppressalis) overcome the adverse situation by entering diapause, wherein development changes dynamically occur and metabolic activity is suppressed. The photoperiod and temperature act as major environmental stimuli of diapause. However, the physiological and molecular mechanisms that interpret the ecologically relevant environmental cues in ontogenetic development during diapause termination are poorly understood. Here, we used genome-wide high-throughput RNA-sequencing to examine the patterns of gene expression during diapause termination in C. suppressalis. Major shifts in biological processes and pathways including metabolism, environmental information transmission, and endocrine signalling were observed across diapause termination based on over-representation analysis, short time-series expression miner, and gene set enrichment analysis. Many new pathways were identified in diapause termination including circadian rhythm, MAPK signalling, Wnt signalling, and Ras signalling, together with previously reported pathways including ecdysteroid, juvenile hormone, and insulin/insulin-like signalling. Our results show that convergent biological processes and molecular pathways of diapause termination were shared across different insect species and provided a comprehensive roadmap to better understand diapause termination in C. suppressalis.