Functional Characterization Of Mir395in Regulation Of Tolerance Of Brassica Napus To Cadmium

MicroRNAs (miRNAs) are a new class of endogenous non-coding small RNAs which widely exist in eukaryotic organisms. They play important roles in biological processes, including development, cell proliferation and stressful responses. miR395plays a role in sulphate assimilation and allocation by controlling expressions of its target genes. Plants may regulate their adaptation to heavy mental stress, e.g. gene expression for sulfate and GSH assimilation. In order to elucidate the mechanism by which miR395regulates plant tolerance to Cd stress, we treated seedlings of Brassica napus with concentrations of Cd2+ranging from20to120μM CdCl2for7d. We found that two rapeseed transgenic lines overexpressing miR395d showed higher biomass, Cd content, and Cd translocation from roots to shoots relative to the wild type. Transgenic plants overexpressing miR395d had a lower content of TBARS than the wild type under40μM Cd stress. By contrast, chlorophyll, NPT and GSH contents were higher in transgenic plants than the wild type. These results suggest that transgenic plants overexpressing miR395can confer plant tolerance to Cd toxicity. We determined sulfate accumulation in plants under the Cd stress. Examination of physiological response reverled that sulfate-deficiency intensified Cd-induced oxidative stress in shoots and roo. However, the transgenic plants showed much higher sulfate content than the wild type. To validate the results, seedlings of transgenic lines and wide type were cultured in soils with CdCl2at20-200mg/kg for30d. The same result was found as described in the seedlings grown hydroponically. Meanwhile, expression of several genes coding for BnPCSl, BnHO1and other proteins was up-regulated under Cd stress, but the expression of the genes in transgenic plants was more pronounced in the wide type. From these results, we concluded that miR395plays an importance role in tolerance of brassica napus to Cd toxicity.