PLANT PHYSIOLOGY , Vol 106, Issue 4 1261-1267, Copyright © 1994 by American Society of Plant Biologists
|
MOLECULAR BIOLOGY AND GENE REGULATION |
Expression of the Arabidopsis Gene Akr Coincides with Chloroplast Development
H. Zhang, J. Wang and H. M. Goodman
Department of Genetics, Harvard Medical School and Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114
Reduced expression of a nuclear gene of Arabidopsis thaliana, Akr, results
in the formation of chlorotic plants due to a block in the
proplastid-to-chloroplast development pathway (H. Zhang, D.C. Scheirer, W.
Fowle, H.M. Goodman [1992] Plant Cell 4: 1575-1588). In an effort to
discern the function of the Akr gene product in chloroplast development,
transgenic plants containing an Akr::[beta]-glucuronidase gene fusion were
constructed to monitor the spatial and temporal patterns of Akr expression.
Akr is expressed only in chloroplast-containing tissues and maximal
expression occurs during the seedling stage, coincident with chloroplast
development. This result is consistent with the hypothesis that Akr is
required at an early stage of chloroplast development. The effects of an
AKR deficiency on the expression of nuclear and plastid genes required for
photosynthetic activity were also examined. Within chloroplast-deficient
leaves of plants in which Akr expression is limited by the presence of Akr
antisense transgenes or truncated Akr sense transgenes, mRNAs for the
nuclear genes Cab2, Cab4, RbcS, and GapA are present at wild-type levels;
similarly, levels of mRNAs for the plastid genes rbcL and psbA are not
affected by the AKR deficiency. Thus, although expression of these
photosynthetic genes is tightly coordinated with the development and
maintenance of chloroplasts in wild-type plants, their expression is
unaffected in AKR-deficient chlorotic leaves. Therefore, we propose that
Akr functions in a pathway different from the one controlling the
expression and regulation of the photosynthetic genes during chloroplast
development, and at a specific developmental stage after the putative
plastid factor is made.