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Summary: Cross‐kingdom RNA interference (RNAi) is a crucial mechanism in host–pathogen interactions, with RNA‐dependent RNA polymerase (RdRP) playing a vital role in signal amplification during RNAi. However, the role of pathogenic fungal RdRP in siRNAs generation and the regulation of plant–pathogen interactions remains elusive.Using deep sequencing, molecular, genetic, and biochemical approaches, this study revealed that VmRDR2 of Valsa mali regulates VmR2‐siR1 to suppress the disease resistance‐related gene MdLRP14 in apple.Both VmRDR1 and VmRDR2 are essential for the pathogenicity of V. mali in apple, with VmRDR2 mediating the generation of endogenous siRNAs, including an infection‐related siRNA, VmR2‐siR1. This siRNA specifically degrades the apple intracellular LRR‐RI protein gene MdLRP14 in a sequence‐specific manner, and overexpression of MdLRP14 enhances apple resistance against V. mali, which can be suppressed by VmR2‐siR1. Conversely, MdLRP14 knockdown reduces resistance.In summary, this study demonstrates that VmRDR2 contributes to the generation of VmR2‐siR1, which silences the host's intracellular LRR protein gene, thereby inhibiting host resistance. These findings offer novel insights into the fungi‐mediated pathogenicity mechanism through RNAi. [ABSTRACT FROM AUTHOR]

Summary: Root‐knot nematodes (RKNs) induce giant cells (GCs) within galls which are characterized by large‐scale gene repression at early stages. However, the epigenetic mechanism(s) underlying gene silencing is (are) still poorly characterized.DNA methylation in Arabidopsis galls induced by Meloidogyne javanica was studied at crucial infection stages (3 d post‐infection (dpi) and 14 dpi) using enzymatic, cytological, and sequencing approaches. DNA methyltransferase mutants (met1, cmt2, cmt3, cmt2/3, drm1/2, ddc) and a DNA demethylase mutant (ros1), were analyzed for RKN resistance/tolerance, and galls were characterized by confocal microscopy and RNA‐seq.Early galls were hypermethylated, and the GCs were found to be the major contributors to this hypermethylation, consistent with the very high degree of gene repression they exhibit. By contrast, medium/late galls showed no global increase in DNA methylation compared to uninfected roots, but exhibited large‐scale redistribution of differentially methylated regions (DMRs). In line with these findings, it was also shown that DNA methylation and demethylation mutants showed impaired nematode reproduction and gall/GC‐development. Moreover, siRNAs that were exclusively present in early galls accumulated at hypermethylated DMRs, overlapping mostly with retrotransposons in the CHG/CG contexts that might be involved in their repression, contributing to their stability/genome integrity. Promoter/gene methylation correlated with differentially expressed genes encoding proteins with basic cell functions. Both mechanisms are consistent with reprogramming host tissues for gall/GC formation.In conclusion, RNA‐directed DNA methylation (RdDM; DRM2/1) pathways, maintenance methyltransferases (MET1/CMT3) and demethylation (ROS1) appear to be prominent mechanisms driving a dynamic regulation of the epigenetic landscape during RKN infection. [ABSTRACT FROM AUTHOR]

Summary: In the plant male germline, transposable elements (TEs) are reactivated in the companion vegetative nucleus, resulting in siRNA production and the intercellular movement of these siRNAs to reinforce TE silencing in sperm. However, the mechanism by which siRNA movement is regulated remains unexplored.Here we show that ARID1, a transcription factor which is constitutively expressed in the vegetative nucleus but dynamically accumulates in the generative cell (the progenitor of sperm) to promote the second pollen mitosis, mediates siRNA movement to reinforce heterochromatic silencing in the male germline.We looked for regulators involved in the accumulation of ARID1 in the generative cell, and found that AGO9, a germline‐specific AGO in Arabidopsis, is required for the accumulation of ARID1 in the generative cell. Mutations in either ARID1 or AGO9 lead to the interruption of not only the second pollen mitosis but also the movement of siRNA from the vegetative nucleus to the male germline, resulting in the release of heterochromatic silencing in the male germline. Moreover, conditional knockdown of ARID1 in the generative cell causes reduced heterochromatic silencing in both bicellular and mature pollen.This study provides insights into how a spatiotemporal transcription factor coordinates heterochromatic silencing and male germline maturation. [ABSTRACT FROM AUTHOR]