Estresse osmótico e do retículo endoplasmático induzem morte celular programada de maneira dependente das proteínas NRPs / Osmotic- and ER-stress induce NRPs-dependent programed cell death

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The identification of cell signaling pathways in response to different stresses and the interactions among these pathways have become major focus for understanding the molecular bases of plant cell-environment interactions. Recently, a novel integrative pathway between ER- and osmotic-stress has been described by our group. Among the target genes of the integrative pathway, N-rich1 and N-rich2 genes, which exhibit the strongest synergistic induction by the combination of both stresses, are homolog of NRP, here designated NRP-A, that has been shown to be specifically associated with programmed cell death. In this investigation, we demonstrated that the N-rich1 and N-rich2 ESTs correspond to the same NRP-A homolog gene, and hence designated NRP-B. Using transgenic plants defective for the unfolded protein response (UPR) activation, we demonstrated that activation of the integrative target genes, NAM, NRP-A and NRP-B, occurs via an ER-stress signaling pathway distinct from the UPR. Likewise, the expression of the three genes is not altered by ABA treatment, indicating that their osmotic induction is ABAindependent. Consistent with an involvement in cell death programs, all three genes are up-regulated by cell death inducers and repressed by senescence inhibitors. Furthermore, the transient expression of NRP-A and NRP-B promoted caspase-3-like activation in soybean protoplasts and accelerated senescence in tobacco leaves. These results revealed the involvement of these proteins in cell death programs. We also demonstrated that NRP-B is located to the plasma membrane, most likely associated to signaling systems, and is capable to promote NAM and NRP-A up-regulation when expressed in soybean protoplasts. Collectively, these results describe a novel branch of the ER stress signaling that integrates with the osmotic signal through a NRP-dependent apoptotic response. As a strategy for engineering stress tolerance in plants, we demonstrated that enhanced accumulation of the molecular chaperone BiP confers abiotic stress tolerance in soybean seedlings in addition to preventing cell death. Ectopic expression of BiP in transgenic soybean plants decreased tunicamycin-induced leaf necrosis and kept leaf turgor under PEG-induced dehydration conditions, resulting in dead cell content lower than that in untransformed plants. The BiP involvement in preventing cell death was further demonstrated by transient expression of NRP-A and NRP-B in sense and antisense BiP- overexpressing tobacco leaves. While in sense leaves senescence was clearly delayed, in antisense leaves the NRP-induced senescence was accelerated as compared to wilt-type leaves. Further experiments are necessary to elucidate the mechanisms by which BiP prevents cell death in plants.

ASSUNTO(S)

nrp upr upr pcd biologia molecular estresse osmótico estresse no retículo er-stress pcd osmotic stress nrp

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