Downy mildew, caused by biotrophic oomycetes such as Hyaloperonospora parasitica, can severely reduce the yield and quality of Brassica crops, especially under cool and humid conditions. Although resistant germplasm and disease-resistance loci have been identified in Brassica rapa, the cellular mechanisms that determine compatible and incompatible host–pathogen interactions are still not fully understood. Autophagy, a conserved cellular recycling process, has emerged as an important regulator of plant immunity, but how oomycete effectors influence autophagy in Brassica crops remains unclear. Due to these challenges, deeper research is needed into how pathogen effectors regulate plant autophagy and disease resistance.
Researchers from the State Key Laboratory of Vegetable Biobreeding, Beijing Vegetable Research Center (BVRC), Beijing Academy of Agriculture and Forestry Science (BAAFS), and collaborating institutions published (DOI: 10.1093/hr/uhaf358) the study on December 31, 2025, in Horticulture Research. The work focuses on the Brassica rapa–Hyaloperonospora parasitica pathosystem and identifies DM459 as a functional reveals that an Arg–x–Leu–Arg (RXLR) effector that interacts with BraATG8i, activates autophagy, stimulates salicylic acid (SA) signaling, and enhances resistance to downy mildew.
The team first confirmed that DM459 is a secreted effector protein and found that its transient expression induced a hypersensitive response and reduced downy mildew symptoms in B. rapa cotyledons. To search for its plant target, they constructed a yeast two-hybrid (Y2H) library from infected leaves and identified BraATG8i, an autophagy-related 8 (ATG8) family protein, as a major DM459-interacting candidate. This interaction was validated through co-immunoprecipitation (Co-IP), luciferase complementation imaging (LCI), bimolecular fluorescence complementation (BiFC), and AlphaFold3-based structural prediction. Functional assays showed that overexpression of the gene BraATG8i increased resistance to H. parasitica, while RNA interference (RNAi)-mediated silencing weakened resistance and increased pathogen growth. The study further showed that DM459 interacts with BraATG4, BraATG3, and BraATG7, proteins required for autophagosome assembly. When autophagy was inhibited by 3-methyladenine (3-MA), plants became more susceptible, while monodansylcadaverine (MDC) staining and transmission electron microscopy (TEM) confirmed that DM459 promotes autophagic activity. The researchers also found that pathogen infection or DM459 expression increased SA accumulation, which in turn activated BraATG8i expression and further strengthened autophagy-associated defense.
The authors said the study offers a different view of oomycete effectors: some are not only tools used by pathogens, but can also become signals that plants convert into defense. In this case, DM459 appears to help assemble the plant's own autophagy machinery, allowing infected cells to mount a stronger immune response. They said this pathway helps explain why resistant B. rapa lines activate stronger defense than susceptible ones, and why autophagy should be viewed as a central layer of crop immunity rather than a background cellular process.
These findings provide both mechanistic insight and practical value for vegetable disease-resistance research. The DM459–BraATG8i module highlights autophagy as a promising target for improving downy mildew resistance in Brassica crops without relying only on chemical control. Because the gene BraATG8i acts as a positive regulator of immunity, it may serve as a useful marker or engineering target in molecular breeding. More broadly, the study suggests that defense-activating effectors can be used to uncover hidden immune pathways in crops. Future work identifying upstream immune receptors, natural promoter variation, and field-level resistance performance could help translate this mechanism into durable disease-control strategies.
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References
DOI
10.1093/hr/uhaf358
Original Source URL
https://doi.org/10.1093/hr/uhaf358
Funding information
This work was supported by the National Natural Science Foundation of China (32102400, 32002045), the Exploratory Research Program (TSXM202505), the Scientist Training Program (JKZX202406) of Beijing Academy of Agriculture and Forestry Science, the earmarked fund for China Agriculture Research System (CARS-23-A03), and the Foundation for Reform and Development of BVRC (KYCX202502).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.