Chen Zhu https://orcid.org/0000-0003-0007-2189, Jia-Hui Liu https://orcid.org/0000-0003-0682-8602, Jian-Hua Zhao https://orcid.org/0000-0003-2554-1930, +5 , Ting Liu https://orcid.org/0000-0003-1632-2808, Yun-Ya Chen https://orcid.org/0000-0001-9958-5245, Chun-Han Wang https://orcid.org/0000-0003-4984-3845, Zhong-Hui Zhang https://orcid.org/0000-0003-3732-8010, Hui-Shan Guo https://orcid.org/0000-0002-3057-9303, and Cheng-Guo Duan

PNAS March 15, 2022 | 119 (12) e2114583119

Significance

Increasing evidence demonstrates that small RNAs can serve as trafficking effectors to mediate bidirectional transkingdom RNA interference (RNAi) in interacting organisms, including plant–pathogenic fungi systems. Previous findings demonstrated that plants can send microRNAs (miRNAs) to fungal pathogen Verticillium dahliae to trigger antifungal RNAi. Here we report that V. dahliae is able to secret an effector to the plant nucleus to interfere with the nuclear export of AGO1–miRNA complexes, leading to an inhibition in antifungal RNAi and increased virulence in plants. Thus, we reveal an antagonistic mechanism that can be exploited by fungal pathogens to counteract antifungal RNAi immunity via manipulation of plant small RNA function.

Abstract

Communication between interacting organisms via bioactive molecules is widespread in nature and plays key roles in diverse biological processes. Small RNAs (sRNAs) can travel between host plants and filamentous pathogens to trigger transkingdom RNA interference (RNAi) in recipient cells and modulate plant defense and pathogen virulence. However, how fungal pathogens counteract transkingdom antifungal RNAi has rarely been reported. Here we show that a secretory protein VdSSR1 (secretory silencing repressor 1) from Verticillium dahliae, a soil-borne phytopathogenic fungus that causes wilt diseases in a wide range of plant hosts, is required for fungal virulence in plants. VdSSR1 can translocate to plant nucleus and serve as a general suppressor of sRNA nucleocytoplasmic shuttling. We further reveal that VdSSR1 sequesters ALY family proteins, adaptors of the TREX complex, to interfere with nuclear export of the AGO1–microRNA (AGO1–miRNA) complex, leading to a great attenuation in cytoplasmic AGO1 protein and sRNA levels. With this mechanism, V. dahliae can suppress the accumulation of mobile plant miRNAs in fungal cells and succedent transkingdom silencing of virulence genes, thereby increasing its virulence in plants. Our findings reveal a mechanism by which phytopathogenic fungi antagonize antifungal RNAi-dependent plant immunity and expand the understanding on the complex interaction between host and filamentous pathogens.

See https://www.pnas.org/doi/10.1073/pnas.2114583119