Conserved Regulation Is Involved in Abiotic Stress Responses in Pitaya ().

() is a conserved microRNA family that targets growth-regulating factors (GRFs), which play significant roles in plant growth and stress responses. Available evidence justifies the idea that -targeted GRFs have important functions in many plant species; however, no genome-wide analysis of the pitaya () gene has yet been reported. Further, its biological functions remain elusive. To uncover the regulatory roles of and its targets, the hairpin sequence of pitaya and the open reading frame (ORF) of its target, , were isolated from pitaya. Phylogenetic analysis showed that the precursor () gene of plants might be clustered into three major groups, and, generally, a more recent evolutionary relationship in the intra-family has been demonstrated. The sequence analysis indicated that the binding site of in is located at the conserved motif which codes the conserved "RSRKPVE" amino acid in the Trp-Arg-Cys (WRC) region. In addition, degradome sequencing analysis confirmed that four GRFs (, c56908.graph_c0; , c52862.graph_c0; , c39378.graph_c0 and , c54658.graph_c0) are targets that are regulated by specific cleavage at the binding site between the 10th and 11th nucleotides from the 5' terminus of . Furthermore, quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that is down-regulated when confronted with drought stress (15% polyethylene glycol, PEG), and its expression fluctuates under other abiotic stresses, i.e., low temperature (4 ± 1 °C), high temperature (42 ± 1 °C), NaCl (100 mM), and abscisic acid (ABA; 0.38 mM). Conversely, the expression of showed the opposite trend to exposure to these abiotic stresses. Taken together, plays a regulatory role in the control of , which might influence the abiotic stress response of pitaya. This is the first documentation of this role in pitaya and improves the understanding of the molecular mechanisms underlying the tolerance to drought stress in this fruit.