Expression of FlHMA3, a P _1B2-ATPase from Festulolium loliaceum, correlates with response to cadmium stress

Heavy metal ATPase 3 (HMA3), a P1B2-ATPase, is a key tonoplast transporter involved in mediating the vacuolar sequestration of cadmium (Cd) to detoxify the intake of this element by plants. HMA3 expression in response to Cd stress has not been previously examined in the grass hybrid species Festulolium loliaceum (Huds.) P. Fourn. In this study, FlHMA3 isolated from F. loliaceum was found to comprise 833 amino acid residues with 77% homology to the rice OsHMA3. Transient expression of FlHMA3 fused to enhanced green fluorescent protein in Arabidopsis protoplasts suggested its localization to vacuolar membranes. Quantitative real-time RT-PCR analysis of F. loliaceum revealed that FlHMA3 is expressed predominantly within roots and up-regulated by excess Cd. Over the 168 h treatment, Cd content of F. loliaceum roots was significantly higher than that of shoots, regardless of external CdCl2 concentrations. A significant positive correlation was found between FlHMA3 expression and Cd accumulation in roots of F. loliaceum seedlings subjected to 10–100 mg L-1 CdCl2 for 168 h or, in a separate experiment, to 25 or 100 mg L-1 CdCl2 for the same duration. These findings provide evidence that FlHMA3 encodes a vacuolar P1B2-ATPase that may play an important role in Cd2+ sequestration into root cell vacuoles, thereby limiting the entry of Cd2+ into the cytoplasm and reducing Cd2+ toxicity.