Mobile microRNAs (miRNAs) responsive to excess nickel in pumpkin (Cucurbita maxima L.)

Abstract

Nickel (Ni) is a toxic heavy metal that inhibits plant growth, development, and reproduction. MicroRNAs (miRNA) travel from cell to cell or organ to carry messages to regulate gene expression. The objective of this study is to find mobile miRNAs that are Ni-responsive and are present in pumpkin (Cucurbita maxima L.) phloem sap. For this purpose, pumpkin seedlings were exposed to Ni (100 μM, NiCl2), and root, shoot, and phloem-sap specimens were collected at 0 (control), 24, and 48 hours of the treatment. The stem-loop RT-qPCR and stem-loop semi-quantitative RT-PCR methods were used to determine the abundance of 14 miRNAs in the phloem sap. Compared to the control, the abundance of miR160, miR167, miR393, miR397, and miR398 are suppressed in Ni-treated seedlings. The reduction was verified by grafting experiments, revealing that miR167 and miR393 are Ni-responsive and move/travel from the leaf-to-root direction. Those phloem-residential miRNAs potentially play a role in the Ni-response mechanism. This study can help to understand the early response mechanism of plants against excess Ni and lead to identifying miRNA-mediated long-distance communication of plants.