中文摘要：

草酸是多种植物病原真菌（如核盘菌，灰葡萄孢等）的重要致病因子，这些草酸产生菌在侵染植物时，会分泌草酸来酸化寄主组织，使得病原真菌的细胞壁降解酶能更迅速地协同发挥作用，加速细胞的降解，而且草酸可夺取寄主细胞壁的钙离子形成草酸钙结晶从而破坏寄主细胞壁。植物microRNA广泛参与植物生长发育各阶段的基因表达调控，在抗生物或非生物胁迫的应答中发挥着重要的作用。本研究基于植物microRNA芯片研究3周龄拟南芥（Arabidopsis thaliana）在30 mmol/L草酸胁迫下microRNA的表达。获得3个差异表达的microRNA：miRNA-2988 （Ptc-miR3911），miRNA-3090 （Ath-miR858），miRNA-3131（Ppt-miR1211）。根据psRNATarget，对下调表达的小立碗藓（Physcomitrella patens） Ppt-miR1211的同源物，找到一个最匹配的靶mRNA是At5g35753；另一下调表达的毛果杨（Populus trichocarpa）Ptc-miR3991（与Ath-miR399b同源）的同源物，对应的靶mRNA是一个泛素连接酶 （At2g33770）；上调表达的Ath-miR858有4个靶mRNA，分别为 At2g47460 （AtMYB12）、At5g49330 （AtMYB111）、At1g06180 （AtMYB13）和At1g66230 （AtMYB20）。草酸胁迫下，qRT-PCR对其中下调表达的两个Ppt-miR1211及Ptc-miR3991同源物的靶基因的表达情况分析表明，At5g35753及At2g33770在草酸胁迫2 h后被诱导表达，于12 h达到峰值，24 h后表达量下降；qRT-PCR还表明：在草酸胁迫1 h后，Ath-miR858确实被诱导表达，于12 h达到峰值，24 h后表达量下降，其靶基因MYB在草酸胁迫早期（2 h内）多数有下调的趋势，表明microRNA对其靶mRNA确有负调控。此外，还对Ath-miR858与Ath-miR399b的启动子进行了生物信息学分析。本研究结果为microRNA在拟南芥抗草酸胁迫中的作用提供了依据。

英文摘要：

Oxalic acid （OA） is an important virulence factor of many plant fungal pathogens, such as Sclerotinia sclerotiorum and Botrytis cinerea. These oxalic acid-producing pathogens can secrete OA to acidify the host organs, leading plant pathogenic cell-wall-degrading enzymes to degrade plant cells more quickly and synergistically. Moreover, oxalic acid can combine calcium to form calcium oxalate crystals, thus destroying the host cell walls. Plant microRNAs are involved in the regulation of plant growth and development and play important roles in the biotic and abiotic stresses. In this paper, the differentially expressed microRNAs of 3-week-old Arabidopsis thaliana under the stress of 30 mmol/L OA were uncovered based on plant microRNA microarray. Three differentially expressed microRNAs were obtained, that was miRNA-2988 （Ptc-miR3911）, miRNA-3090 （Ath-miR858） and miRNA-3131 （Ppt-miR1211）. Among them, one down-regulated microRNA was the homolog of Physcomitrella patens Ppt-miR1211, whose target mRNA was an unkown gene At5g35753 based on psRNATarget, the other down-regulated microRNA was the homolog of Populus trichocarpa Ptc-miR3911, which was identical to Ath-miR399b, and its target mRNA was a ubiquitin-conjugating E2 enzyme At2g33770, The only up-regulated differentially expressed microRNA was Ath-miR858, whose target mRNAs were transcription factors At2g47460 （AtMYB12）, At5g49330 （AtMYB111）, At1g06180 （AtMYB13） and At1g66230 （AtMYB20）. qRT-PCR analyzed the expression profiles of the target genes of the two down-regulated miRNAs, the expression of At5g35753 and At2g33770 was induced at 2 h, peaked at 12 h, and decreased at 24 h with the challenge of oxalic acid. qRT-PCR analysis also showed that Ath-miR858 was induced at 1 h, peaked at 12 h, and decreased at 24 h under the stress of oxalic acid, however, the expression of most of its target mRNAs were decreased at the early stage （within 2 h） of OA stress, indicating the negatively-regulated function of microRNAs. Moreover, the b