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<p>Helper-component proteinase (HC-Pro), encoded by potyviruses, function as viral suppressors of RNA silencing (VSRs). Despite their conserved role, HC-Pros share approximately 40% similarity, implying potential differences in VSR efficiency, particularly in their ability to inhibit HEN1 methyltransferase activity. This study investigated the inhibitory potential of HC-Pros from different potyviruses in transgenic plants. P1/HC-Pro from turnip mosaic virus (P1/HC-Pro<sup>Tu</sup>) exhibited the most potent inhibition of HEN1, followed by P1/HC-Pro from zucchini yellow mosaic virus (P1/HC-Pro<sup>Zy</sup>), while P1/HC-Pro from tobacco etch virus (P1/HC-Pro<sup>Te</sup>) showed the weakest inhibitory effect. These differential effectual effects corresponded to variations in unmethylated microRNAs (unMet-miRNAs) accumulation across the transgenic lines. Fluorescence resonance energy transfer (FRET) analysis indicated that HC-Pro<sup>Tu</sup> recruits HEN1 and ATG8a to HC-Pro bodies (H-bodies) and indirectly associates with AGO1, potentially influencing the assembly of the RNA-induced silencing complex (RISC) and leading to the accumulation of free-form miRNA duplexes. The ability of HC-Pro<sup>Tu</sup> to sequester HEN1 and AGO1 in H-bodies may, therefore, modulate miRNA loading. This observation aligns with the finding that <i>P1/HC-Pro</i><sup><i>Tu</i></sup> plants harbored approximately 50% unMet-miRNAs and exhibited the lowest AGO1 levels, suggesting a positive correlation between HEN1 inhibition and autophagic degradation of AGO1. Interestingly, unMet-miRNAs are absent in the AGO1 of <i>P1/HC-Pro</i><sup><i>Tu</i></sup> plants but reappeared in <i>P1/HC-Pro</i><sup><i>Tu</i></sup><i>/hen1-8/heso1-1</i> plants, accompanied by signs of AGO1 recovery. These findings highlight the functional diversity of HC-Pro VSRs and provide new insights into their differential effects on miRNA methylation, RISC assembly, and the regulation of RNA silencing pathways.</p>

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HC-Pro inhibits HEN1 methyltransferase activity, leading to autophagic degradation of AGO1

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年3月13日

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  • Zhao-Jun Pan,
  • Wei-Lun Wei,
  • Phuong-Anh Tran,
  • Ru-Ying Fang,
  • Thanh Ha Pham,
  • John L. Bowman,
  • Chao-Tzu Chung,
  • Bing-Nan Shen,
  • Ju-Ting Yang,
  • Han-Han Chang,
  • Wann-Neng Jane,
  • Chiung-Hsiang Cheng,
  • Chia-Chi Wang,
  • Hsin-Yi Wu,
  • Syuan-Fei Hong,
  • Qian-Wen Shang,
  • Sin-Fen Hu,
  • Pin-Chun Lin,
  • Fu-Hui Wu,
  • Choun-Sea Lin,
  • Yu-Ling Hung,
  • Tang-Long Shen,
  • Shih-Shun Lin

摘要

Helper-component proteinase (HC-Pro), encoded by potyviruses, function as viral suppressors of RNA silencing (VSRs). Despite their conserved role, HC-Pros share approximately 40% similarity, implying potential differences in VSR efficiency, particularly in their ability to inhibit HEN1 methyltransferase activity. This study investigated the inhibitory potential of HC-Pros from different potyviruses in transgenic plants. P1/HC-Pro from turnip mosaic virus (P1/HC-ProTu) exhibited the most potent inhibition of HEN1, followed by P1/HC-Pro from zucchini yellow mosaic virus (P1/HC-ProZy), while P1/HC-Pro from tobacco etch virus (P1/HC-ProTe) showed the weakest inhibitory effect. These differential effectual effects corresponded to variations in unmethylated microRNAs (unMet-miRNAs) accumulation across the transgenic lines. Fluorescence resonance energy transfer (FRET) analysis indicated that HC-ProTu recruits HEN1 and ATG8a to HC-Pro bodies (H-bodies) and indirectly associates with AGO1, potentially influencing the assembly of the RNA-induced silencing complex (RISC) and leading to the accumulation of free-form miRNA duplexes. The ability of HC-ProTu to sequester HEN1 and AGO1 in H-bodies may, therefore, modulate miRNA loading. This observation aligns with the finding that P1/HC-ProTu plants harbored approximately 50% unMet-miRNAs and exhibited the lowest AGO1 levels, suggesting a positive correlation between HEN1 inhibition and autophagic degradation of AGO1. Interestingly, unMet-miRNAs are absent in the AGO1 of P1/HC-ProTu plants but reappeared in P1/HC-ProTu/hen1-8/heso1-1 plants, accompanied by signs of AGO1 recovery. These findings highlight the functional diversity of HC-Pro VSRs and provide new insights into their differential effects on miRNA methylation, RISC assembly, and the regulation of RNA silencing pathways.