Poster: Photosynthesis

Abs # 371: Functional analysis of CtpA in transgenic arabidopsis plants

Presenter:	Chen, Sophia Y, sophia.y.chen@monsanto.com
Authors	Chen, Sophia Y (A)   Duff, Stephen M (A)   Fabbri, Bradon J (A)   Anderson, John C (A)   Oliver, Robyn  (B)   CaJacob, Claire A (A)
Affiliations:	(A): Monsanto Company (B): Tyco Health Care

Photosystem II (PSII) is an essential part of the photosynthetic apparatus in plants that uses light energy to split water, releasing oxygen, protons and electrons. CtpA (carboxyl-terminal processing protease) catalyzes the conversion of pre-D1 (pD1) protein into the active form of D1, which is an integral part of PSII. Since the D1 protein is continuously removed from the PSII and replaced, the active CtpA is constantly required under light conditions. By over-expressing CtpA sense and antisense mRNAs in Arabidopsis plants, we have generated transgenic Arabidopsis plants with reduced level of CtpA protein and plants with elevated level of CtpA protein. Transgenic plants with severely reduced levels of CtpA protein exhibit a bleached/chlorotic phenotype and stunted growth. The mutant phenotypes can be further enhanced by bright illumination. However, plants with a slight reduction of CtpA protein do not exhibit the mutant phenotype and cannot be distinguished from wild-type plants under normal growth conditions. Several CtpA enzyme inhibitors were shown to have herbicidal activity in planta. Interestingly, plants that produce excessive amount of CtpA protein were shown to be resistant to these inhibitors. Our results suggest that CtpA is essential for plant growth and development due to its critical role in photosynthesis. A reduced amount of CtpA, however, is sufficient to carry out its essential function.