PLANT PHYSIOLOGY , Vol 103, Issue 4 1291-1297, Copyright © 1993 by American Society of Plant Biologists
|
MOLECULAR BIOLOGY AND GENE REGULATION |
DNA Replication-Dependent Histone H2A mRNA Expression in Pea Root Tips
E. Y. Tanimoto, T. L. Rost and L. Comai
Section of Plant Biology, Division of Biological Sciences, University of California, Davis, California 95616-8537 (E.Y.T., T.L.R.)
Histone H2A mRNA is selectively expressed in scattered subpopulations of
cells in the pea (Pisum sativum) root apical meristem. To study whether
this specific expression was associated with the cell cycle, a
double-labeling technique was used to identify cells replicating DNA during
S phase and those expressing H2A mRNA. Cells in S phase were detected by
[3H]thymidine incorporation and autoradiography, whereas cells containing
H2A mRNA were identified by in situ hybridization using digoxigenin-labeled
probes. Approximately 92% of the [3H]thymidine-labeled S-phase cells
expressed H2A mRNA and 85% of cells that expressed H2A mRNA were in S
phase. In root tissue located basal to the promeristem, synchronous
co-located expression was observed in scattered packets of proliferating
cells. Furthermore, neither H2A mRNA nor S-phase cells could be detected
within the quiescent center or mature root cap. When DNA synthesis was
inhibited with hydroxyurea, a commensurate and specific decrease in
steady-state levels of H2A mRNA was found. We conclude that cell-specific
expression of pea histone H2A mRNA is replication dependent and that H2A
mRNA is transiently accumulated during a period of the cell cycle that
mostly overlaps the S phase. We propose that the overlap between H2A
expression and S phase could occur if H2A mRNA accumulation began in late
G1 and abated in late S.
