Poster: Photosynthesis
Abs #
382: Characterization of NADP-ME in a C4 system that lacks Kranz anatomy
|
|
Presenter: |
Estavillo, Gonzalo M, monsa@ufl.edu |
Authors | Estavillo, Gonzalo M (A) Rao, Srinath k (A) Bowes, George (A) | | Affiliations: |
(A): Department of Botany, University of Florida, Gainesville FL 32611 USA
|
|
|
Hydrilla verticillata typically exists as a C3 plant, but growth at low [CO2] induces a C4 photosynthetic system that lacks Kranz anatomy. In this system, NADP malic enzyme (NADP-ME) provides rubisco with a high [CO2] specifically in the chloroplasts. We have shown that NADP-ME activity and protein amount increase as C4 photosynthesis is induced, and this NADP-ME is localized in the chloroplasts. We have cloned and partially characterized an NADP-ME isoform that was expressed only in C3 Hydrilla leaves. The complete cDNA sequence (HvMe1) was 2631 bp long with an ORF of 1964 bp that encoded a protein of 654 amino acids. The putative transit peptide was comprised of 75 amino acids. A predicted molecular mass of 72 kD correlated with Western blot data. This isoform showed 82% homology with an Aloe arborescens CAM isoform. Expression studies suggested that transcription of HvMe1 was subject to diel regulation. The first signal appeared 2 h before the light period, but had a half-life of about 90 min, and completely disappeared by the end of the light period. HvMe1 transcripts were detected in leaves of C3 plants, but not in those of C4, or roots. In preliminary phylogenetic analyses this isoform grouped with the monocots and was closest to a maize embryonic form. From the expression studies, it appears unlikely that HvMe1 is the C4 photosynthetic isoform. However, light extracts from both C3 and C4 leaves exhibit NADP-ME activity, but when the pH is raised to 8.3 only the C4 extracts exhibit activity, which suggests that a yet to be cloned isoform, with distinct kinetics, is present in C4 leaves. The isolation of two different genomic NADP-ME clones is consistent with this notion. Supported by USDA NRICGP 98-35306-6449.
