Comparative analysis of cadmium responsive microRNAs in roots of two Ipomoea aquatica Forsk. cultivars with different cadmium accumulation capacities.

In plants, microRNAs (miRNAs) play regulatory roles in response to various environmental stresses. In order to illustrate the regulation mechanisms of miRNAs involving the different Cd accumulation abilities between a low-shoot-Cd cultivar (QLQ) and a high-shoot-Cd cultivar (T308) of water spinach (Ipomoea aquatic Forsk.), six sRNA libraries at 3 different time points were constructed. Only 5 miRNAs were exclusively regulated in QLQ, among them, miRNA395 was up-regulated, which was supposed to enhance the Cd retention and detoxification in root. Also, the alterations of miRNA5139, miRNA1511 and miRNA8155 contributed to the attenuation of Cd translocation into the shoot of QLQ. More differentially expressed miRNAs were observed in T308, indicating more complex response was adopted by T308 under Cd stress. miRNA397 exclusively regulated in T308 has enhanced the Cd influx of T308 under Cd treatments. Besides, the Cd translocation of T308 was strengthened due to the up-regulation of MATE efflux family, which was targeted by miRNA3627. Our results unraveled the effects of the cultivar-dependent expression of these specific miRNAs on the different Cd accumulation and translocation abilities of QLQ and T308. These findings provide a new perspective for the molecular assisted breeding of low-Cd cultivars for leaf-vegetables.