Plant Physiol, August 2002, Vol. 129, pp. 1600-1606
Overexpression of the clpP 5'-Untranslated Region in
a Chimeric Context Causes a Mutant Phenotype, Suggesting Competition
for a clpP-Specific RNA Maturation Factor in Tobacco
Chloroplasts1
Hiroshi
Kuroda and
Pal
Maliga*
Waksman Institute, 190 Frelinghuysen Road, Rutgers, The State
University of New Jersey, Piscataway, New Jersey
08854-8020
The plastid ribosomal RNA (rrn) operon
promoter was fused with DNA segments encoding the leader sequence
(5'-untranslated region [UTR]) of plastid mRNAs to compare their
efficiency in mediating translation of a bacterial protein neomycin
phosphotransferase (NPTII) in tobacco (Nicotiana
tabacum) chloroplasts. In young leaves, NPTII accumulated at
0.26% and 0.8% of the total soluble leaf protein from genes with the
clpP and atpB 5'-UTR, respectively. Interestingly, expression of NPTII from the promoter with the clpP 5'-UTR (0.26% NPTII) caused a mutant (chlorotic)
phenotype, whereas plants accumulating approximately 0.8% NPTII from
the atpB 5'-UTR were normal green, indicating that the
mutant phenotype was independent of NPTII accumulation. Low levels of
monocistronic clpP mRNA and accumulation of
intron-containing clpP transcripts in the chlorotic
leaves suggest competition between the clpP 5'-UTR in
the chimeric transcript and the native clpP pre-mRNA
(ratio 16:1) for an mRNA maturation factor. Because maturation of 11 other intron-containing mRNAs was unaffected in the chlorotic leaves,
it appears that the factor is clpP specific. The mutant phenotype is correlated with reduced levels (approximately 2 times) of
the ClpP1 protease subunit, supporting an important role for ClpP1 in
chloroplast development.
1
This work was supported by the National Science
Foundation (grant nos. MCB 96-30763 and MCB 99-05043) and by Monsanto
Co. (to P.M.).
*
Corresponding author; e-mail maliga{at}waksman.rutgers.edu; fax
732-445-5735.
© 2002 American Society of Plant Physiologists
