The brown planthopper (BPH) impacts both rice yield and quality. The exogenous application of abscisic acid (ABA) and jasmonic acid (JA) has been previously shown to induce rice resistance to BPH; however, the regulation of rice-mediated defense by these plant growth regulators is unclear. We applied exogenous JA and ABA to rice and analyzed molecular responses to BPH infestation. Nine RNA libraries were sequenced, and 6218 differentially expressed genes (DEGs) were generated and annotated. After ABA + BPH and JA + BPH treatments, 3491 and 2727 DEGs, respectively, were identified when compared with the control (BPH alone). GO enrichment and KEGG pathway analysis showed that the expression of several JA pathway genes (OsAOS2, encoding allene oxide synthase; OsOPR, 12-oxo-phytodienoic acid reductase; and OsACOX, acy1-CoA oxidase) were significantly up-regulated after ABA + BPH treatment. Furthermore, exogenous JA increased the expression of genes involved in ABA synthesis. Meanwhile, the expression levels of genes encoding WRKY transcription factors, myelocytomatosis protein 2 (MYC2) and basic leucine zippers (bZIPs) were up-regulated significantly, indicating that ABA and JA might function together to increase the expression of transcription factors during the rice defense response. The DEGs identified in this study provide vital insights into the synergism between ABA and JA and further contribute to the mechanistic basis of rice resistance to BPH.

Drought stress greatly impacts insect development and population growth. Some studies have demonstrated increased reproductive capacity in drought-stressed insects; however, physiological changes in the brown planthopper (BPH), Nilaparvata lugens (Stål), during periods of drought are unclear. In this study, BPH fed on drought- stressed rice had lower population numbers than BPH feeding on non-stressed rice. Water content, osmotic pressure of hemolymph and total amino acid content of BPH were significantly lower when BPH fed on drought-stressed rice compared to the non-stressed control; however, glucose content and glutathione S-transferase (GST) activity were significantly higher in BPH fed on drought-stressed rice. The expression of Vitellogenin and Exuperantia in BPH fed on drought-stressed rice was higher than that in BPH feeding on non-stressed control plants. The size of myofibrils and the abundance of mitochondria in BPH flight muscles were significantly lower in BPH fed on drought-stressed rice compared to non-stressed plants. These results indicate that water management impacts the physiology of BPH, which may be useful in understanding the relationship between drought stress and this damaging herbivore.

Serotonin is a well-known secondary metabolite that plays an important role in many growth and developmental processes, as well as biotic and abiotic stress responses of plants. Yet, whether serotonin biosynthesis regulates the resistance of rice to the brown planthopper (BPH) Nilaparvata lugens and its underling mechanisms have not been entirely investigated. In this study, we found that expression levels of four serotonin biosynthesis gene, OsTDC1, OsTDC2, OsTDC3, and OsT5H, and the serotonin content were significantly induced by BPH nymph infestation. The rice seedlings pretreated with serotonin were more attractive to BPH nymphs and promoted their feeding behavior as indicated by increased honeydew excretion. In addition, serotonin application to artificial diets increased the survival rates of BPH nymphs in a dose-dependent manner compared to the controls. Moreover, the exogenous serotonin application to rice seedlings increased the average injury scale and functional plant loss indices caused by BPH nymph infestation. Moreover, supplemented serotonin enhanced soluble sugar and free amino acid contents, as well as the activities of SOD, POD, and PPO, but repressed the production of flavonoids. Our findings illustrated that serotonin plays a negative role in the regulation of rice resistance to BPH nymphs probably by modulating contents of soluble sugars, free amino acids, and flavonoids.

Volatile organic compounds (VOCs) have garnered substantial research interest in recent years due to their biodegradability, low toxicity, and potent antimicrobial properties against various plant pathogens. As a typical herbivore-induced plant volatile (HIPV) elicited by Nilaparvata lugens (Brown planthopper, BPH), (E)-2-hexenal has been identified as a promising natural antimicrobial agent. In this study, we investigated the protective potential of (E)-2-hexenal against Rhizoctonia solani (R. solani) in rice, focusing on both its direct antifungal activity and host-mediated defense mechanisms. In vitro antifungal assays demonstrated that treatment with 100 μL/mL (E)-2-hexenal resulted in a 91.07% inhibition of R. solani mycelial growth after 48 h. Scanning electron microscopy (SEM) observation and chitinase activity analysis revealed that (E)-2-hexenal suppressed fungal growth by disrupting the structural integrity of the pathogen cell wall. Furthermore, 100 μL/mL (E)-2-hexenal effectively conferred protection to detached rice leaves. Whole-plant inoculation assays confirmed that (E)-2-hexenal pretreatment significantly alleviated disease symptoms and triggered systemic resistance in rice plants. Physiological and biochemical analyses showed that (E)-2-hexenal treatment enhanced the activities of defense-related enzymes, elevated hydrogen peroxide (H₂O₂) levels, and promoted the accumulation of defensive metabolites in rice leaves. HPLC-MS quantification further revealed significant increases in the endogenous levels of jasmonic acid (JA) and salicylic acid (SA). Transcriptomic KEGG pathway enrichment analysis indicated that differentially expressed genes (DEGs) were mainly involved in alpha-linolenic acid metabolism, diterpenoid biosynthesis, phenylpropanoid biosynthesis, plant–pathogen interaction, and plant hormone signal transduction. Collectively, these results suggest that (E)-2-hexenal enhances rice resistance to sheath blight disease via a dual-action mechanism: direct inhibition of fungal development and activation of host immune responses. Our findings highlight the potential application of (E)-2-hexenal and other VOCs in developing eco-friendly strategies for sustainable rice disease management.

Due to their role as the main pollinators in agricultural environments, honeybees help improve crop quality and yield and also help maintain global and ecosystem biodiversity. However, pesticide exposure during foraging has resulted in declining honeybee populations, and there are increasing concerns about the potential adverse effects of the herbicide glyphosate (Gly) on honeybees. In this study, we show that exogenous melatonin (Mel) alleviated Gly toxicity in honeybees, and we investigated the mechanisms underlying Mel’s effects using RNA-seq and 16S rRNA sequencing. We show that the survival rate of honeybees exposed to Gly increased significantly after pretreatment with 10 mg/L exogenous Mel in the laboratory. RNA-seq showed that genes involved in immunity, digestion, the nervous system, carbohydrate and amino acid metabolism, and development were altered after Gly treatment; interestingly, pretreatment with Mel had a compensatory effect on transcription in response to Gly. 16S rRNA sequencing revealed that Mel treatment dramatically improved the abundance of lactic acid bacteria in honeybees. These findings reveal how melatonin protects honeybee intestines from glyphosate-induced damage, offering practical strategies for honeybee conservation.