Abstract：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 bioinformatic analyses were conducted with the promoters of Ath-miR858 and Ath-miR399b. Our results provide the foundation of microRNAs in the role of oxalic acid stress.
