Expression of Brassica napus cell number regulator 6 (BnCNR6) in Arabidopsis thaliana confers tolerance to copper

Copper is an essential but potential toxic micro-nutrient in rapeseed. So far, little is known about the mechanism of rapeseed Cu transport and detoxification. Here, we determined the function of Cu transporter, Brassica napus cell number regulator 6 (BnCNR6), in regulating Cu homeostasis. BnCNR6 exhibited higher expression level in euphylla and root tips. It was found that in protoplasts and transgenic plants expressing Pro35S:BnCNR6-GFP, BnCNR6 was localized to the plasma membrane (PM). Expression of BnCNR6 in the yeast (Saccharomyces cerevisiae), compensated the Cu hypersensitivity of Δcup2 by promoting Cu²⁺ efflux. The overexpression of BnCNR6 in Arabidopsis athma5 mutant restored its growth, increased its photosynthesis, and reduced Cu²⁺ concentration in the roots. Furthermore, the roots of BnCNR6 overexpression lines had lower net Cu influx than in those of the athma5 mutant. These results revealed that BnCNR6 is a PM protein which is useful for detoxification to increase tolerance to Cu toxicity. Collectively, our study provides a theoretical basis for reducing Cu stress in rapeseed.