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Abstract The identification effector targets and characterization of their functions are crucial for understanding pathogen infection mechanisms and components of plant immunity. Here, we identify the effector UgsL, a ustilaginoidin synthetase with a key role in regulating virulence of the rice false smut fungus Ustilaginoidea virens. Heterologous expression of UgsL in rice (Oryza sativa) enhances plant susceptibility to multiple pathogens, and host-induced gene silencing of UgsL enhances plant resistance to U. virens, indicating that UgsL inhibits rice immunity. UgsL interacts with STRUBBELIG RECEPTOR KINASE 3 (OsSRF3). Genome editing and overexpression of OsSRF3 demonstrate that OsSRF3 plays a pivotal role in the resistance of rice to multiple pathogens. Remarkably, overexpressing OsSRF3 enhances resistance without adversely affecting plant growth or yield. We show that BRASSINOSTEROID RECEPTOR-ASSOCIATED KINASE 1 (OsBAK1) interacts with and phosphorylates OsSRF3 to activate pathogen-triggered immunity, inducing the mitogen-activated protein kinase cascade, a reactive oxygen species burst, callose deposition, and expression of defense-related genes. UgsL interferes with the phosphorylation of OsSRF3 by OsBAK1. Furthermore, UgsL mediates OsSRF3 degradation by facilitating its association with the ubiquitin-26S proteasome. Our results reveal that OsSRF3 positively regulates immunity in rice and that UgsL mediates its degradation, thereby inhibiting the activation of OsBAK1–OsSRF3-mediated immune pathways.

The harlequin ladybird, Harmonia axyridis, is a valuable asset in integrated pest management (IPM); however, issues related to low-temperature storage and transportation have resulted in low hatching rate, while the use of pesticides may lead to non-target effects against this natural enemy during field application. Fluctuating thermal regimes (FTR) have been shown to be beneficial during the low-temperature storage, and the type and concentration of insecticides used are crucial for field application of H. axyridis. Despite this, little research has been conducted on the effects of FTR on the hatching rate of ladybird eggs, and the impact of pesticides on their egg viability remains unclear. To address these gaps, we investigated the effects of different thermal temperatures, recovery frequencies (the number of changes in temperature conditions per unit time), and recovery durations (the duration of the treated temperature condition) on egg hatching under constant low-temperature conditions. We also examined the toxicity and safety of seven commonly used insecticides on egg hatching. Our results indicate that the temperature during FTR application did not significantly affect egg hatching, but the interaction between temperature and recovery frequency can significantly affect egg hatching. Moreover, the recovery frequency and recovery duration had a significant impact on hatching. Under specific conditions, the hatching rate of eggs subjected to FTR was similar to that of eggs stored at 25 °C. Furthermore, we found that matrine (a kind of alkaloid pesticide isolated from Sophora flavescens) had low toxicity to ladybird eggs and is a safe pesticide for use in conjunction with this natural enemy. The study provides valuable information on effectively managing H. axyridis by taking into account both storage temperature and pesticide exposure.

Rice false smut caused by Ustilaginoidea virens is a serious disease of rice (Oryza sativa), severely reducing plant mass and yields worldwide. We performed genome-wide analysis of the CCHC-type zinc-finger transcription factor family in this pathogen. We identified and functionally characterized seven UvCCHC genes in U. virens. The deletion of various UvCCHC genes affected the stress responses, vegetative growth, conidiation, and virulence of U. virens. ∆UvCCHC5 mutants infected rice spikelets normally but could not form smut balls. Sugar utilization experiments showed that the ∆UvCCHC5 mutants were defective in the utilization of glucose, sucrose, lactose, stachyose, and trehalose. Deletion of UvCCHC5 did not affect the expression of rice genes associated with grain filling, as revealed by RT-qPCR. We propose that the ∆UvCCHC5 mutants are impaired in transmembrane transport, and the resulting nutrient deficiencies prevent them from using nutrients from rice to form smut balls. RNA-seq data analysis indicated that UvCCHC4 affects the expression of genes involved in mitochondrial biogenesis, ribosomes, transporters, and ribosome biogenesis. These findings improve our understanding of the molecular mechanism underlying smut ball formation in rice by U. virens.