Up-regulation of stress-inducible genes in tobacco and <Emphasis Type="Italic">Arabidopsis</Emphasis> cells in response to abiotic stresses and ABA treatment correlates with dynamic changes in histone H3 and H4 modifications

Animal cells react to mitogenic or stress stimuli by rapid up-regulation of immediate-early (IE) genes and a parallel increase in characteristic modifications of core histones: chromatin changes, collectively termed the nucleosomal response. With regard to plants little is known about the accompanying changes at the chromatin level. We have used tobacco BY-2 and Arabidopsis T87 cell lines to study the nucleosomal response of plant cells to high salinity, cold and exogenous abscisic acid (ABA). When in quiescent stage, both tobacco and Arabidopsis cells show the typical nucleosomal response to high salinity and cold stress, manifested by rapid transient up-regulation of histone H3 Ser-10 phosphorylation, immediately followed by transient up-regulation of H3 phosphoacetylation and histone H4 acetylation. For each of the studied stresses the observed nucleosomal response was strictly correlated with the induction of stress-type specific genes. The dynamics of histone modifications in BY-2 cells in response to exogenous ABA exhibited a more complex pattern than that evoked by the two abiotic stresses, probably due to superposition of the primary and secondary effects of ABA. A rapid increase in H3 Ser-10 phosphorylation was also observed in whole leaves subjected to high salinity; however, the rate of change in this modification was much slower than in cultured cells. Together, these results indicate that the quiescent BY-2 and T87 cell lines show a typical nucleosomal response to abiotic stresses and ABA treatment and may represent suitable models for the study of chromatin-mediated mechanisms of stress tolerance in plants.