Poster: Organelle biogenesis

Abs # 635: Genetic analysis of SecY function in Arabidopsis

Presenter:	Fernandez, Donna E., dfernand@wisc.edu
Authors	Skalitzky, Courtney A. (A)   Hankinson, Jessica A. (A)   Heck, Gregory R. (A)   Fernandez, Donna E. (A)
Affiliations:	(A): University of Wisconsin-Madison

The Arabidopsis genome contains two SecY genes, which encode related, but distinct proteins. We have isolated and characterized Arabidopsis mutants with T-DNA insertions in the SECY loci (At2g18710 and At2g31530). SECY1 has been previously characterized as a component of the translocation channel for the Sec pathway in the thylakoids. Homozygous Arabidopsis secY1 embryos are pale rather than green during seed development, and give rise to pale seedlings that arrest before making leaves. SECY2 also appears to be directed to plastids; however, based on sequence comparisons, the mature AtSECY2 protein is more closely related to bacterial SecY proteins than to AtSECY1. Homozygous secY2 mutants arrest at the globular stage of embryogenesis. Therefore both SECY1 and SECY2 are essential genes and the gene products act non-redundantly in Arabidopsis. Non-redundant activity can be based on expression differences rather than differences in gene product function. To investigate this issue, we performed promoter swapping experiments. These results of these experiments indicate that expression differences cannot account for the difference in the mutant phenotypes. Instead, we conclude that SECY1 and SECY2 perform different functions in plant cells. Supported by UW-Madison Graduate School.