AUTHOR=Kim Yeon-Ok , Gwon Yonghyun , Kim Jangho 

TITLE=Exogenous Cysteine Improves Mercury Uptake and Tolerance in Arabidopsis by Regulating the Expression of Heavy Metal Chelators and Antioxidative Enzymes

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.898247

DOI=10.3389/fpls.2022.898247

ISSN=1664-462X

ABSTRACT=<p>Cysteine (Cys) is an essential amino acid component of the major heavy metal chelators, such as glutathione (GSH), metallothioneins (MTs), and phytochelatins (PCs), which are involved in the pathways of mercury (Hg) tolerance in plants. However, the mechanism through which Cys facilitates Hg tolerance in plants remains largely unclear. In this study, we investigated the effects of exogenous Cys on Hg uptake in the seedlings, roots, and shoots of <italic>Arabidopsis</italic> throughout 6 and 36 h of Hg exposure and on the regulation of Hg detoxification by heavy metal chelators and antioxidative enzymes. The results showed that exogenous Cys significantly improved Hg tolerance during the germination and seedling growth stages in <italic>Arabidopsis</italic>. Exogenous Cys significantly promoted Hg uptake in <italic>Arabidopsis</italic> roots by upregulating the expression of the Cys transporter gene <italic>AtLHT1</italic>, resulting in increased Hg accumulation in the roots and seedlings. In <italic>Arabidopsis</italic> seedlings, exogenous Cys further increased the Hg-induced glutathione synthase (<italic>GS1</italic> and <italic>GS2</italic>) transcript levels, and the Hg and Hg + Cys treatments greatly upregulated <italic>MT3</italic> expression after 36 h exposure. In the roots, <italic>MT3</italic> was also significantly upregulated by treatment of 36 h of Hg or Hg + Cys. Notably, in the shoots, <italic>MT2a</italic> expression was rapidly induced (10-fold) in Hg presence and further markedly increased (20-fold) by exogenous Cys. Moreover, in the seedlings, exogenous Cys upregulated the transcripts of all superoxide dismutase (<italic>CuSOD1</italic>, <italic>CuSOD2</italic>, <italic>MnSOD1</italic>, <italic>FeSOD1</italic>, <italic>FeSOD2</italic>, and <italic>FeSOD3</italic>) within 6 h and subsequently increased the Hg-induced <italic>GR1</italic> and <italic>GR2</italic> transcript levels at 36 h, all of which could eliminate the promotion of reactive oxygen species production and cell damage caused by Hg. Additionally, exogenous Cys upregulated all the antioxidative genes rapidly in the roots and subsequently increased the expression of <italic>CuSOD1</italic>, <italic>CuSOD2</italic>, and <italic>MnSOD1</italic> in the shoots. These results indicate that exogenous Cys regulates the transcript levels of heavy metal chelators and antioxidative enzymes differently in a time- and organ-specific manner under Hg stress. Taken together, our study elucidates the positive functional roles of exogenous Cys in the Hg uptake and tolerance mechanisms of <italic>Arabidopsis</italic>.</p>