PLANT PHYSIOLOGY , Vol 106, Issue 2 673-678, Copyright © 1994 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
Nuclear Mutation Inhibits Expression of the Chloroplast Gene That Encodes the Large Subunit of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase
S. Hong and R. J. Spreitzer
Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68583-0718
Chlamydomonas reinhardtii mutant 76-5EN was recovered as a light-sensitive,
acetate-requiring strain that failed to complement a chloroplast structural
gene mutant of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC
4.1.1.39). Further genetic analysis revealed that the new mutation was
inherited in a mendelian pattern, indicating that it resides within the
nucleus. The 76-5EN mutant lacks Rubisco holoenzyme but has wild-type
levels of whole-chain electron transport activity and chlorophyll. During a
1-min pulse labeling with 35SO42-, little or no Rubisco large-subunit
synthesis occurred in the mutant. Nuclear-encoded small subunits were
synthesized to a normal level and were subsequently degraded. When analyzed
by northern hybridization, the 76-5EN mutant was found to have a decreased
level of large-subunit mRNA. Large-subunit mRNA synthesis also appeared to
be reduced during a 10-min pulse labeling with [32P]orthophosphate, but the
labeled mRNA was stable during a 1-h chase. These results indicate that a
nuclear gene mutation specifically disrupts the accumulation of
large-subunit mRNA within the chloroplast. A deeper understanding of the
nature of the 76-5EN gene may be useful for manipulating the expression of
the agronomically important Rubisco enzyme.
