SpHMA1 is a chloroplast cadmium exporter protecting photochemical reactions in the Cd hyperaccumulator Sedum plumbizincicola

• Published in: Plant, cell and environment Vol. 42; no. 4; pp. 1112 - 1124
• Main Authors: Zhao, Haixia, Wang, Liangsheng, Zhao, Fang‐Jie, Wu, Longhua, Liu, Anna, Xu, Wenzhong
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.04.2019
• Subjects: Accumulation; Adenosine triphosphatase; Adenosine Triphosphatases - metabolism; Baking yeast; Blotting, Southern; Cadmium; cadmium (Cd); Cadmium - metabolism; Chlorophyll; chloroplast; Chloroplasts; Chloroplasts - metabolism; CRISPR; CRISPR/Cas9; Detoxification; Fluorescence; heavy metal ATPase 1 (HMA1); Heavy metals; hyperaccumulator; Leaves; Membrane Transport Proteins - metabolism; Organisms, Genetically Modified; Photochemical reactions; Photochemicals; Photosynthesis; Photosystem II; Plant Leaves - metabolism; Plant Proteins - metabolism; Proteins; Real-Time Polymerase Chain Reaction; Ribonucleic acid; RNA; RNA-mediated interference; Saccharomyces cerevisiae; Sedum - metabolism; Sedum - physiology; Sedum plumbizincicola; Toxicity; Transgenic plants; transporter; heavy metal ATPase 1 (HMA1); Sedum plumbizincicola; hyperaccumulator; CRISPR/Cas9; chloroplast; transporter; cadmium (Cd)
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.13456

Sedum plumbizincicola is able to hyperaccumulate cadmium (Cd), a nonessential and highly toxic metal, in the above‐ground tissues, but the mechanisms for its Cd hypertolerance are not fully understood. Here, we show that the heavy metal ATPase 1 (SpHMA1) of S. plumbizincicola plays an important role in chloroplast Cd detoxification. Compared with the HMA1 ortholog in the Cd nonhyperaccumulating ecotype of Sedum alfredii, the expression of SpHMA1 in the leaves of S. plumbizincicola was >200 times higher. Heterologous expression of SpHMA1 in Saccharomyces cerevisiae increased Cd sensitivity and Cd transport activity in the yeast cells. The SpHMA1 protein was localized to the chloroplast envelope. SpHMA1 RNA interference transgenic plants and CRISPR/Cas9‐induced mutant lines showed significantly increased Cd accumulation in the chloroplasts compared with wild‐type plants. Chlorophyll fluorescence imaging analysis revealed that the photosystem II of SpHMA1 knockdown and knockout lines suffered from a much higher degree of Cd toxicity than wild type. Taken together, these results suggest that SpHMA1 functions as a chloroplast Cd exporter and protects photosynthesis by preventing Cd accumulation in the chloroplast in S. plumbizincicola and hyperexpression of SpHMA1 is an important component contributing to Cd hypertolerance in S. plumbizincicola. Cadmium is a highly toxic metal and accumulates in the leaves to very high levels in Cd hyperaccumulators in Sedum plumbizincicola, posing a high risk of Cd toxicity to the chloroplasts. In this study, we demonstrate that SpHMA1 is a Cd exporter localized to the chloroplast envelope, functioning to detoxify Cd in the chloroplasts to protect photosynthetic reactions in S. plumbizincicola. The hyperexpression of SpHMA1 in the leaves of S. plumbizincicola, compared with SaHMA1n in a nonhyperaccumulating ecotype S. alfredii, likely confers an adaptive advantage under Cd stress conditions and contributes to Cd hypertolerance in S. plumbizincicola. These novel findings have important implications for the evolution of metal hyperaccumulation phenotype and the adaptation of plants to metal‐contaminated environments.