The H1 histone variant of tomato, H1-S, is targeted to the nucleus and accumulates in chromatin in response to water-deficit stress

Water deficit has a significant impact on patterns of gene expression. Base d on the deduced amino acid sequence, it has been proposed that the drought and abscisic acid-induced gene (his1-s) of tomato (Lycopersicon esculentum Mill.) encodes an H1 histone variant. To study the role of H1-S it is impo rtant to understand the expression characteristics of the protein. To ident ify the his1-s product in vivo the his1-s cDNA was fused to a (His)(6) tag and overexpressed in Escherichia coli. The H1-S fusion protein was used to generate an antibody that recognized a protein with an apparent molecular w eight of 31 kDa that accumulates in response to water deficit in the whole plant and detached leaves. A time course of his1-s expression showed that p rotein accumulation is delayed compared to the mRNA accumulation in both th e whole plant and detached leaves. Cellular fractionation, immunofluorescen ce and H1-S::beta-glucuronidase fusion analyses in transgenic tissues were used to determine the cellular localization of H1-S. The results showed tha t H1-S accumulates in nuclei and is associated with chromatin of wilted tom ato leaves. The drought- and abscisic acid-induced gene his1-s encodes a li nker-histone subtype specifically accumulated in the nuclei and chromatin o f tomato leaves subjected to water-deficit conditions. Although the molecul ar mechanism of H1-S function is still unclear, the expression characterist ics of H1-S are consistent with a potential role of this protein in the reg ulation of gene expression in response to water deficit.