Cell-specific expression of plant histone H2A genes.

Abstract

Histone H2A is a component of eukaryotic chromatin whose expression has not been studied in plants. We isolated and characterized a tomato and a pea cDNA encoding histone H2A. We found that in tomato H2A is encoded by a small gene family and that both the pea and the tomato mRNAs are polyadenylated. Tomato H2A has 82% amino acid residue identity to pea H2A, 83% to wheat, and 65% to human and yeast H2A. Plant H2As differ from fungal and animal H2As in their amino-terminal and carboxy-terminal regions. Carboxy-terminal plant H2A regions contain the motif SPKK, a peptide implicated in binding of A/T-rich DNA regions. By using RNA gel blot analysis, we determined that the steady-state mRNA level of these genes was abundant in apices and early developing fruit and very low in mature tissues. In situ RNA hybridization showed strong spatial regulation because the mRNA was abundant in some cells and not detectable in others. In tomato shoot tips, H2A-expressing cells were distributed irregularly in or near meristems. In tomato or pea root tips, expressing cells were concentrated near the apex, and their distribution was consistent with that expected of cycling cells. Other H2A transcripts were found in nondividing cortical cells that are known to undergo endoduplication during the late maturation phase of primary development.

A meristem-related gene from tomato encodes a dUTPase: analysis of expression in vegetative and floral meristems.

“…This may be accomplished by This pattern deviates sharply from that of other genes whose expression was found to be associated with meristems. Histone H2A, the only other identified gene with high expression levels in shoot meristems, is expressed in single scattered cells of the shoot apex and derived tissues in a pattern that is consistent with that expected of cycling cells (Koning et al, 1991). Other, as yet unidentified, "apexspecific" genes in tobacco (Kelly et al, 1990) or cauliflowercurd-specific genes (Medford et al, 1991) are expressed only in subdomains of meristematic zones rather than in the homogeneous pattern exhibited by dUTPase.…”

Molecular cloning, sequence analysis and differential expression of an intron‐containing gene encoding tomato histone H1

“…The expression of the maize H1 mRNA also follows this pattern [21], but in the only other case reported (Arubidopsis), no difference in steadystate mRNA levels was found [lo]. Koning et al [19] have shown that histone H2A mRNA levels in both tomato and pea vary with the tissue origin of the RNA sample and/or stage of development, with a greater abundance of mRNA in apices and early developing fruit. Thus, there seems to be a general correlation between the amount of histone mRNA and the meristem component of the tissues and/or the degree to which cells are actively cycling in the tissues.…”

“…In contrast, the Volvox [20] and most animal cell histone H1 mRNAs are non-polyadenylated, and those which are generally fit into the category of developmental variants or replication-independent variants. Messenger RNAs encoding core histones in plants have also been shown to be polyadenylated [4,19,27,281, again in contrast to the animal core histone mRNAs.…”

Constitutive Expression Exposes Functional Redundancy between the Arabidopsis Histone H2A Gene HTA1 and Other H2A Gene Family Members

“…Although several plant histone H2A genes have been identified and their expression patterns analyzed (Koning et al, 1991;Callard and Mazzolini, 1997;Huh et al, 1997;van den Heuvel et al, 1999;Xu et al, 1999), their functions have not yet been well defined. We have identified an Arabidopsis thaliana mutant, rat5, in which the histone H2A gene HTA1 is disrupted.…”