The ER luminal binding protein (BiP) alleviates Cd(2+)-induced programmed cell death through endoplasmic reticulum stress-cell death signaling pathway in tobacco cells

Abstract

Cadmium (Cd) is very toxic to plant cells and Cd(2+) stress induces programmed cell death (PCD) in Nicotiana tabacum L. cv. bright yellow-2 (BY-2) cells. In plants, PCD can be regulated through the endoplasmic reticulum (ER) stress-cell death signaling pathway. However, the mechanism of Cd(2+)-induced PCD remains unclear. In this study, we found that Cd(2+) treatment induced ER stress in tobacco BY-2 cells. The expression of two ER stress markers NtBLP4 and NtPDI and an unfolded protein response related transcription factor NtbZIP60 were upregulated with Cd(2+) stress. Meanwhile, the PCD triggered by prolonged Cd(2+) stress could be relieved by two ER chemical chaperones, 4-phenylbutyric acid and tauroursodeoxycholic acid. These results demonstrate that the ER stress-cell death signaling pathway participates in the mediation of Cd(2+)-induced PCD. Furthermore, the ER chaperone AtBiP2 protein alleviated Cd(2+)-induced ER stress and PCD in BY-2 cells based on the fact that heterologous expression of AtBiP2 in tobacco BY-2 cells reduced the expression of NtBLP4 and a PCD-related gene NtHsr203J under Cd(2+) stress conditions. In summary, these results suggest that the ER stress-cell death signaling pathway regulates Cd(2+)-induced PCD in tobacco BY-2 cells, and that the AtBiP2 protein act as a negative regulator in this process.

Keywords: ATF/CREB homolog 1; ATF6; BY-2; BiP; BiP protein; Bright yellow-2 cells; Ca; Cadmium; Cd; ER; ER stress; GRP94; Hac1; IRE1; N-rich protein; NRP; PCD; PDI; PERK; PKR-like ER kinase; Programmed cell death; UPR; X-box binding protein 1; Xbp1; activating transcription factor 6; bZIP; basic-leucine zipper; bright yellow-2; cadmium; calcium; endoplasmic reticulum; glucose-regulated protein 94; inositol-requiring enzyme-1; luminal binding protein; programmed cell death; protein disulfide isomerase; unfolded protein response.