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Abstract
The molecular chaperone binding protein (BiP) participates in the constitutive function of the endoplasmic reticulum (ER) and protects the cell against stresses. In this study, we investigated the underlying mechanism by which BiP protects plant cells from stress-induced cell death. We found that enhanced expression of BiP in soybean (Glycine max) attenuated ER stress- and osmotic stress-mediated cell death. Ectopic expression of BiP in transgenic lines attenuated the leaf necrotic lesions that are caused by the ER stress inducer tunicamycin and also maintained shoot turgidity upon polyethylene glycol-induced dehydration. BiP-mediated attenuation of stress-induced cell death was confirmed by the decreased percentage of dead cell, the reduced induction of the senescence-associated marker gene GmCystP, and reduced DNA fragmentation in BiP-overexpressing lines. These phenotypes were accompanied by a delay in the induction of the cell death marker genes N-RICH PROTEIN-A (NRP-A), NRP-B, and GmNAC6, which are involved in transducing a cell death signal generated by ER stress and osmotic stress through the NRP-mediated signaling pathway. The prosurvival effect of BiP was associated with modulation of the ER stress- and osmotic stress-induced NRP-mediated cell death signaling, as determined in transgenic tobacco (Nicotiana tabacum) lines with enhanced (sense) and suppressed (antisense) BiP levels. Enhanced expression of BiP prevented NRP- and NAC6-mediated chlorosis and the appearance of senescence-associated markers, whereas silencing of endogenous BiP accelerated the onset of leaf senescence mediated by NRPs and GmNAC6. Collectively, these results implicate BiP as a negative regulator of the stress-induced NRP-mediated cell death response.
Highlights
The molecular chaperone binding protein (BiP) participates in the constitutive function of the endoplasmic reticulum (ER) and protects the cell against stresses
We directly addressed this issue by testing the effect of BiP overexpression on a typical ER stress-induced cell death event
Ectopic expression of BiP in transgenic lines attenuated the leaf necrotic lesions that are caused by tunicamycin, a potent inducer of ER stress and cell death in soybean, and promoted the maintenance of shoot turgidity under polyethylene glycol (PEG)-induced dehydration conditions, whereas untransformed control leaves wilted under similar PEG treatment conditions
Summary
The molecular chaperone binding protein (BiP) participates in the constitutive function of the endoplasmic reticulum (ER) and protects the cell against stresses. We recently identified a novel branch of the ER stress signaling pathway that diverges from the molecular chaperone-inducing branch of the UPR and transduces a programmed cell death (PCD) signal This pathway integrates the ER stress and osmotic stress signals to synergistically increase the expression of N-rich proteins (NRP-A and NRP-B) and a NAC domain-containing protein, GmNAC6, which are critical mediators of stress-induced cell death in plants (Irsigler et al, 2007; Costa et al, 2008; Pinheiro et al, 2009). Our results provide new insights into the protective properties of plant BiP against stresses and indicate that BIP may play an important role in protecting cells from cell death by modulating the NRP-mediated stress response
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