MsYSL6, A Metal Transporter Gene of Alfalfa, Increases Iron Accumulation and Benefits Cadmium Resistance.

Iron (Fe) is necessary for plant growth and development. The mechanism of uptake and translocation in Cadmium (Cd) is similar to iron, which shares iron transporters. Yellow stripe-like transporter (YSL) plays a pivotal role in transporting iron and other metal ions in plants. In this study, MsYSL6 and its promoter were cloned from leguminous forage alfalfa. The transient expression of MsYSL6-GFP indicated that MsYSL6 was localized to the plasma membrane and cytoplasm. The expression of MsYSL6 was induced in alfalfa by iron deficiency and Cd stress, which was further proved by GUS activity driven by the MsYSL6 promoter. To further identify the function of MsYSL6, it was heterologously overexpressed in tobacco. MsYSL6-overexpressed tobacco showed better growth and less oxidative damage than WT under Cd stress. MsYSL6 overexpression elevated Fe and Cd contents and induced a relatively high Fe translocation rate in tobacco under Cd stress. The results suggest that MsYSL6 might have a dual function in the absorption of Fe and Cd, playing a role in the competitive absorption between Fe and Cd. MsYSL6 might be a regulatory factor in plants to counter Cd stress. This study provides a novel gene for application in heavy metal enrichment or phytoremediation and new insights into plant tolerance to toxic metals.

MsNRAMP2 Enhances Tolerance to Iron Excess Stress in Nicotiana tabacum and MsMYB Binds to Its Promoter.

Iron(Fe) is a trace metal element necessary for plant growth, but excess iron is harmful to plants. Natural resistance-associated macrophage proteins (NRAMPs) are important for divalent metal transport in plants. In this study, we isolated the MsNRAMP2 (MN_547960) gene from alfalfa, the perennial legume forage. The expression of MsNRAMP2 is specifically induced by iron excess. Overexpression of MsNRAMP2 conferred transgenic tobacco tolerance to iron excess, while it conferred yeast sensitivity to excess iron. Together with the MsNRAMP2 gene, MsMYB (MN_547959) expression is induced by excess iron. Y1H indicated that the MsMYB protein could bind to the "CTGTTG" cis element of the MsNRAMP2 promoter. The results indicated that MsNRAMP2 has a function in iron transport and its expression might be regulated by MsMYB. The excess iron tolerance ability enhancement of MsNRAMP2 may be involved in iron transport, sequestration, or redistribution.