PLANT PHYSIOLOGY , Vol 114, Issue 3 801-815, Copyright © 1997 by American Society of Plant Biologists
|
GENE REGULATION AND MOLECULAR GENETICS |
C4 Gene Expression in Photosynthetic and Nonphotosynthetic Leaf Regions of Amaranthus tricolor
D. McCormac, J. J. Boinski, V. C. Ramsperger and J. O. Berry
Department of Biological Sciences, State University of New York, Buffalo, New York 14260
Throughout most of its growth and development, Amaranthus tricolor produces
fully green leaves. However, near the onset of flowering, unique leaves
emerge that consist of three distinct color regions: green apices, yellow
middle regions, and red basal regions. The green apices are identical to
fully green leaves in terms of pigment composition, photosynthetic
function, and C4 gene expression. The yellow and red regions possess
greatly reduced levels of chlorophyll and they lack photosynthetic
activity. The absence of photosynthetic capacity in the nongreen leaf
regions was associated with three distinct alterations in C4 gene
expression. First, there was a reduction in the translation of C4
polypeptides, and in the yellow regions synthesis of the
ribulose-1,5-bisphosphate carboxylase small subunit occurred in the absence
of large subunit synthesis. Second, there was a reduction in the relative
transcription rates of two plastid-encoded photosynthetic genes, rbcL and
psbA. Third, there was a loss of bundle-sheath cell-specific accumulation
of the rbcL and RbcS mRNAs (but not the polypeptides, which remained
bundle-sheath-specific). This study indicates that alterations in
photosynthetic activity or developmental processes responsible for the loss
of activity can influence C4 gene expression at multiple regulatory levels.
