Browsing by Author "Zhao, Hongwei"

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Arabidopsis Argonaute 2 Regulates Innate Immunity via miRNA393*-Mediated Silencing of a Golgi-Localized SNARE Gene, MEMB12
(2011-05-06)
Zhang, Xiaoming
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Zhao, Hongwei
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Gao, Shang
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Wang, Wei-Chi
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Katiyar-Agarwal, Surekha
Argonaute (AGO) proteins are critical components of RNA silencing pathways that bind small RNAs and mediate gene silencing at their target sites. We found that Arabidopsis AGO2 is highly induced by the bacterial pathogen Pseudomonas syringae pv. tomato (Pst). Further genetic analysis demonstrated that AGO2 functions in antibacterial immunity. One abundant species of AGO2-bound small RNA is miR393b*, which targets a Golgi-localized SNARE gene, MEMB12. Pst infection downregulates MEMB12 in a miR393b*-dependent manner. Loss of function of MEMB12, but not SYP61, another intracellular SNARE, leads to increased exocytosis of an antimicrobial pathogenesis-related protein, PR1. Overexpression of miR393b* resembles memb12 mutant in resistance responses. Thus, AGO2 functions in antibacterial immunity by binding miR393b* to modulate exocytosis of antimicrobial PR proteins via MEMB12. Since miR393 also contributes to antibacterial responses, miR393*/miR393 represent an example of a miRNA*/miRNA pair that functions in immunity through two distinct AGOs: miR393* through AGO2 and miR393 through AGO1.
Fungal Small RNAs Suppress Plant Immunity by Hijacking Host RNA Interference Pathways
(2013-10-04)
Weiberg, Arne
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Wang, Ming
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Lin, Feng-Mao
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Zhao, Hongwei
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Zhang, Zhihong
Botrytis cinerea, the causative agent of gray mold disease, is an aggressive fungal pathogen that infects more than 200 plant species. Here, we show that some B. cinerea small RNAs (Bc-sRNAs) can silence Arabidopsis and tomato genes involved in immunity. These Bc-sRNAs hijack the host RNA interference (RNAi) machinery by binding to Arabidopsis Argonaute 1 (AGO1) and selectively silencing host immunity genes. The Arabidopsis ago1 mutant exhibits reduced susceptibility to B. cinerea, and the B. cinerea dcl1 dcl2 double mutant that can no longer produce these Bc-sRNAs displays reduced pathogenicity on Arabidopsis and tomato. Thus, this fungal pathogen transfers "virulent" sRNA effectors into host plant cells to suppress host immunity and achieve infection, which demonstrates a naturally occurring cross-kingdom RNAi as an advanced virulence mechanism.
Hypoxia-responsive miRNAs target argonaute 1 to promote angiogenesis
(2013-03-01)
Chen, Zhen
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Lai, Tsung-Ching
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Jan, Yi-Hua
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Lin, Feng-Mao
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Wang, Wei-Chi
Despite a general repression of translation under hypoxia, cells selectively upregulate a set of hypoxia-inducible genes. Results from deep sequencing revealed that Let-7 and miR-103/107 are hypoxia-responsive microRNAs (HRMs) that are strongly induced in vascular endothelial cells. In silico bioinformatics and in vitro validation showed that these HRMs are induced by HIF1 alpha and target argonaute 1 (AGO1), which anchors the microRNA-induced silencing complex (miRISC). HRM targeting of AGO1 resulted in the translational desuppression of VEGF mRNA. Inhibition of HRM or overexpression of AGO1 without the 3' untranslated region decreased hypoxia-induced angiogenesis. Conversely, AGO1 knockdown increased angiogenesis under normoxia in vivo. In addition, data from tumor xenografts and human cancer specimens indicate that AGO1-mediated translational desuppression of VEGF may be associated with tumor angiogenesis and poor prognosis. These fmdings provide evidence for an angiogenic pathway involving HRMs that target AGO1 and suggest that this pathway may be a suitable target for anti- or proangiogenesis strategies.