Reference "Characterization of the gene for pyruvate,orthophosphate dikinase from rice, a C3 plant, and a comparison of structure and expression between C3 and C4 genes for this protein"

Reference ID

1605

Title

Characterization of the gene for pyruvate,orthophosphate dikinase from rice, a C3 plant, and a comparison of structure and expression between C3 and C4 genes for this protein

Source

Plant molecular biology, 1997, vol. 34, pp. 701-716

Authors (6)

Imaizumi-N	Ku-M-S
Ishihara-K	Samejima-M
Kaneko-S	Matsuoka-M

Abstract

To investigate the molecular changes that might have occurred in genes for
pyruvate,orthophosphate dikinase (PPDK) during the evolution of C4 plants from
C3 plants, we isolated a full-length cDNA and the corresponding gene for a C4-
like PPDK from rice, a C3 gramineous plant and compared their structures and
promoter activities to those of the corresponding gene from maize, a C4
gramineous plant. As in maize, there are at least two ppdk genes in rice and one
of them was very similar to the maize C4-type ppdk. The deduced amino acid
sequence of the rice PPDK was 88% homologous to the maize C4-type PPDK in the
mature peptide region and 56% homologous in the transit peptide region. The C4-
like ppdk in rice contained 21 exons, which were interrupted by twenty introns,
and the positions of the introns were essentially the same as those in the gene
from maize, with the except in that the gene from rice had two extra introns.
Such extra introns were also found in the C4-type ppdk from a dicot, Flaveria,
at the same positions. These results strongly suggest that the two introns were
present in an ancestral gene before the divergence of monocot and dicot plants.
The C4-like ppdk in rice contained two functionally independent promoters had
generated a larger transcript with the transit peptide region and a smaller
transcript without this region. The unusual dual-promoter system for
transcription has been conserved in the C4-type ppdk gene from maize, indicating
that the dual-promoter system is a common feature of ppdk genes in both C3 and
C4 plants. The patterns of expression of the two transcripts in rice were
different: the larger transcript was expressed exclusively in green leaves at a
low level whereas the smaller transcript was expressed in some reproductive
organs at a high level. Essentially the same patterns of expression were
observed in maize, but the level of expression of the larger transcript in maize
green leaves was much higher than that in green leaves of rice. The promoter
activities of the rice and maize genes for PPDK were examined directly in a
transient expression assay in maize mesophyll protoplasts after electroporation
with promoter::beta- glucuronidase chimeric genes. The rice promoter for the
smaller transcript was very active in the protoplasts but the rice promoter for
the larger transcript had relatively low activity. By contrast, both promoters
of the maize gene had high activity. Taken together, these results demonstrate
that the rice C4-like ppdk is very similar to the maize C4-type ppdk, not only
in terms of primary structure but also in terms of the regulation of expression,
with the exception that the strength of the maize promoter for the larger
transcript is higher. The results strongly suggest that the genetic alterations
required to give rise to the C4-type ppdk gene were relatively limited.