THE PLANT CELL, Vol 3, Issue 7 737-744, Copyright © 1991 by American Society of Plant Biologists
Post-Transcriptional Regulation of Catalase Isozyme Expression in Cotton Seeds
W. Ni and R. N. Trelease
Department of Botany, Arizona State University, Tempe, Arizona 85287-1601
We reported previously that expression of the five tetrameric catalase
isozymes during postgerminative growth of cotton seedings was a consequence
of interactions between two subunits (SU 1 and SU 2) temporally synthesized
from two distinct catalase genes. In this study, we focused on the
regulation of the expression of these two catalase subunits during the
changeover from glyoxysomal to leaf-type peroxisomal metabolism. The
steady-state level of glyoxysomal SU 1 protein (present in 12-hour-old
seeds) increased through day 3 and then declined linearly through day 6,
whereas SU 2 protein (first detected in 24-hour-old seeds) increased
continuously through day 6. The time courses for steady-state levels of the
mRNAs encoding these two subunits revealed two clearly separated peaks: the
first at day 1 (SU 1) and the other at day 4 (SU 2). Accumulation of these
mRNAs preceded the accumulation of their corresponding proteins by at least
24 hours, suggesting temporal, pretranslational regulation of synthesis of
both subunits. Results from run-on transcriptional assays with isolated
nuclei, however, revealed that transcripts encoding both subunits were
synthesized together on days 1 through 5. Hence, it appears that the
accumulations of SU 1 and SU 2 mRNAs are controlled primarily at the
post-transcriptional level, which has not been reported for catalase or any
other eukaryotic peroxisomal enzymes. The accumulation of SU 1 mRNA is not
light dependent, whereas the accumulation of SU 2 mRNA, which directs
synthesis of the predominant subunit comprising the leaf-type peroxisomal
isozyme, occurs only after exposure of seedlings to light.
