Constitutive and light-induced DNAseI hypersensitive sites in the rbcS genes of pea (Pisum sativum)

Permeabilized Arabidopsis protoplasts provide new insight into the chromatin structure of plant alcohol dehydrogenase genes

New data from permeabilized protoplasts have expanded our view of the 5'DNase I hypersensitive area of the Arabidopsis Adh gene derived from nuclei. DNase I hypersensitivity analyses conducted with permeabilized protoplasts from Arabidopsis cell cultures indicates that there are four distinct sites of hypersensitivity centered around positions -425, -325, -200, and -60. The hypersensitive site at -200 coincides with an in vitro hypersensitive site created by purified transcription factors bound to a G-box element. The G-box is a functional cis element that plays a role in the signal transduction of hypoxia and other stresses in Adh. The data presented in this paper support the notion that G-box-related elements may also play a role in defining chromatin structure. The new Arabidopsis data are discussed within the context of what is known about the chromatin structures and regulation of two other plant Adh genes; maize Adh1 and Adh2. The chromatin of the maize Adh1 promoter is divided into a region that is constitutively hypersensitive to DNase I (-700 to -160) and an inducibly hypersensitive region (-140 and -40). There are several sequence elements within the hypersensitive regions bound by proteins in vivo. The anaerobic response element is the most well characterized and functions in the detection of hypoxia. The maize Adh2 gene promoter is constitutively hypersensitive to DNase I, with the exception of a small region that extends to include the TATA box as the gene becomes active. Several cis elements in the Adh2 promoter are bound by factors in vivo. One, at -160, is a functional element that acts as an activator in vascular tissue. The overall goal of our research with the Adh genes from maize and Arabidopsis is to gain further insight into the relationships between the regulation of gene transcription and chromatin structure in plants as it is clear that all the necessary components that characterize regulated gene activity may not be found simply by elucidating the linear sequence of nucleotides that lie 5' to the protein coding regions and finding proteins capable of binding the promoter in vitro.

Cell-specific accumulation of maize phosphoenolpyruvate carboxylase is correlated with demethylation at a specific site greater than 3 kb upstream of the gene

Development of the C4 photosynthetic pathway relies upon the cell-specific accumulation of photosynthetic enzymes. Although the molecular basis of this cell-specific gene expression is not known, regulation appears to be exerted at the level of transcript accumulation. We have investigated the relationship between gene expression patterns and DNA methylation for genes of two of the C4 photosynthetic enzymes, ribulose bisphosphate carboxylase (RuBPCase) and phosphoenolpyruvate carboxylase (PEPCase). We found no correlation between methylation state and gene expression for either the large subunit or a small subunit gene of RuBPCase. In contrast, demethylation of a specific site 5' to the PEPCase gene was correlated with the light-induced, cell-specific accumulation of PEPCase mRNA. This differentially methylated site is positioned at great distance (greater than 3 kb) from the start of transcription. This observation is made more interesting by the fact that the immediate 5' region of the gene, and some of the coding region, represents an unmethylated CpG island. Such islands are normally associated with constitutively expressed genes.