Chaperone function of Arabidopsis NPR1

To cope with diverse environmental stresses, the sessile organisms of plants have evolved diverse defense molecules and signaling systems to transfer the stress signals into downstream metabolic cascades and induce the expression of defense-associated genes. Among the defense systems, the Arabidopsis nonexpressor of pathogenesis-related protein 1 (AtNPR1) playing a key role in a plant systemic acquired immune responses has been shown to have multiple functions. The molecular structure of AtNPR1 has two domains, BTB/POZ and ANK repeat, that are involved in protein–protein interactions. Despite the function of its salicylic acid-induced defense activity in nucleus, the biochemical property of its cytosolic oligomers has not been elucidated. Based on the results that the reversible structural change of redox proteins is a typical property of molecular chaperones, we investigated the biochemical characteristics of AtNPR1 after expressing it in E. coli and purifying the protein. From the study, the recombinant AtNPR1 functions as a protein chaperone to protect plants from heat stress through its structural switching by its oligomer form. Under heat-induced (43 °C) condition, the AtNPR1 protein prevents from aggregation of substrate, MDH. And the structural change was regulated upon the redox changes, such as DTT treatment dissociated its structure to monomer and reduced its chaperone activity, suggesting that the heat-induced chaperone activity of AtNPR1 is dependent on its redox status. In summary, the cytosolic AtNPR1 oligomer performs the important function of molecular chaperone to protect plants from heat stress that can be applied to the preparation of heat shock-tolerant useful crops.