Illumina sequencing revealed roles of microRNAs in different aluminum tolerance of two citrus species.

Self-germinated seedlings of and were supplied with nutrient solution with 0 mM AlCl·6HO (control, -Al) or 1 mM AlCl·6HO (+Al) for 18 weeks. The DW (Dry weights) of leaf, stem, shoot and the whole plant of were decreased and the ratio of root DW to shoot DW in were increased by Al, whereas these parameters of were not changed by Al. Al treatment dramatically decreased the sulfur (S) content in roots and the phosphorus (P) content in both and roots. More Al was transported to shoots and leaves in than in under Al treatment. Al treatment has more adverse effects on than on , as revealed by the higher production of superoxide anion (O ), HO and thiobarbituric acid reactive substace (TBARS) content in roots. Via the Illumina sequencing technique, we successfully identified and quantified 12 and 16 differentially expressed miRNAs responding to Al stress in and roots, respectively. The possible mechanism underlying different Al tolerance of and were summarized as having following aspects: (a) enhancement of adventitious and lateral root development (miR160); (b) up-regulation of stress and signaling transduction related genes, such as , and (miR477, miR397 and miR398); (c) enhancement of citrate secretion (miR3627); (d) more flexible control of alternative glycolysis pathway and TCA cycle (miR3627 and miR482); (e) up-regulation of S-metabolism (miR172); (f) more flexible control of miRNA metabolism. For the first time, we showed that root development (miR160) and cell wall components (cas-miR5139, csi-miR12105) may play crucial roles in Al tolerance in citrus plants. In conclusion, our study provided a comprehensive profile of differentially expressed miRNAs in response to Al stress between two citrus plants differing in Al tolerance which further enriched our understanding of the molecular mechanism underlying Al tolerance in plants.