Gene silencing exists in eukaryotic organisms as a conserved regulation of the gene expression mechanism. In general, small RNAs (sRNAs) are produced within the eukaryotic cells and incorporated into an RNA‐induced silencing complex (RISC) within cells. However, exogenous sRNAs, once delivered into cells, can also silence target genes via the same RISC. Here, we explored this concept by targeting the Cellulose synthase A3 (CesA3) gene of Hyaloperonospora arabidopsidis (Hpa), the downy mildew pathogen of Arabidopsis thaliana. Hpa spore suspensions were mixed with sense or antisense sRNAs and inoculated onto susceptible Arabidopsis seedlings. While sense sRNAs had no obvious effect on Hpa pathogenicity, antisense sRNAs inhibited spore germination and hence infection. Such inhibition of infection was not race‐specific, but dependent on the length and capping of sRNAs. Inhibition of infection by double stranded sRNA was more efficient than that observed with antisense sRNA. Thus, exogenous sRNA targeting conserved CesA3 could suppress Hpa infection in Arabidopsis, indicating the potential of this simple and efficient sRNA‐based approach for deciphering gene functions in obligate biotrophic pathogens as well as for R‐gene independent control of diseases in plants.

中文翻译：

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小RNA抑制霜霉病原体透明假单胞菌拟南芥的感染。

基因沉默存在于真核生物中，作为基因表达机制的保守调控。通常，小RNA（sRNA）在真核细胞内产生，并整合入细胞内的RNA诱导沉默复合体（RISC）中。但是，外源sRNA一旦传递到细胞中，也可以通过相同的RISC使靶基因沉默。在这里，我们通过针对拟南芥霜霉病菌透明质酸菌（Hpa）的纤维素合酶A3（CesA3）基因进行了研究。将Hpa孢子悬浮液与有义或反义sRNA混合，并接种到易感的拟南芥幼苗上。虽然有义sRNA对Hpa没有明显影响致病性，反义sRNA抑制孢子萌发并因此感染。这种对感染的抑制作用不是种族特异性的，而是取决于sRNA的长度和上限。双链sRNA对感染的抑制作用比反义sRNA更为有效。因此，靶向保守CesA3的外源sRNA可以抑制拟南芥中的Hpa感染，这表明这种简单有效的基于sRNA的方法有可能破译专性生物营养性病原体的基因功能以及R基因独立控制植物的疾病。