Poster: Photosynthesis (carbon)
Abs #
236: Molecular characterization and expression of Rubisco activase from thermally contrasting ecotypes of Acer rubrum L.
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Presenter: |
Weston, David J., djwesto@clemson.edu |
Authors | Weston, David J. (A) Bauerle, William L. (A) Swire-Clark, Ginger A. (A) Baird, Wm. Vance (A) | | Affiliations: |
(A): Clemson University
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We are interested in the role of Rubisco activase in thermal adaptation of two divergent ecotypes of Acer rubrum (L.). Florida and Minnesota lines have respective photosynthetic temperature optima of 28-36oC and 25-31oC. Using probes from partial cDNA clones, Southern blot analysis indicates the presence of a single activase (rca) gene in the A. rubrum genome. However, Western analysis probed with anti-tobacco activase revealed the presence of two activase polypeptides designated RCAI and RCAII. Using RT-PCR and DNA sequencing, we found that rca mRNA had two different 3’ ends due to an alternative splicing event at the last intron, resulting in a 39 bp insertion encoding an inframe stop codon. Thus, the longer transcript encodes the smaller RCAI polypeptide, while the smaller transcript encodes the larger RCAII polypeptide. The activase sequences displayed 97% nucleotide homology and 98% amino acid identity. Both the Florida and Minnesota lines were exposed to control 25oC/25oC (day/night) and elevated 35oC/25oC (day/night) air temperatures, and their activase transcript and protein levels were examined. Leaf rca mRNA accumulated but rcaI and rcaII transcript abundance did not directly relate to treatment. Interestingly, the Minnesota line showed increased levels of both RCAI and RCAII polypeptides after three days of treatment at elevated temperature. Previous research has identified activase as a heat labile component of the photosynthetic apparatus. These results show that activase from the heat sensitive ecotype increases at elevated temperature, suggesting a possible adaptive role in photosynthetic thermal acclimation.
