PARENT SESSION

Symposium S1C Photosynthate transport and transporters
Monday August 30th, 2004 10:20 AM-12:20 PM Room 510A
Chair: Andreas Weber
Co-Chair: Marinus Pilon

Investigations on the mechanism of ATP transport across the chloroplast thylakoid membrane in Arabidopsis thaliana. Sophie Thuswaldner^*,1, Cornelia Spetea¹, ¹ Division of Cell Biology, Linköping, Sweden

ABSTRACT- The chloroplast thylakoid membrane is the site for the light-driven reactions of photosynthesis, supplying energy in the form of ATP for CO₂-fixation in the soluble stroma. The utilization of ATP in the lumenal space of the thylakoid has not been considered in the past. Recent results of our research group indicate the presence of nucleotide-dependent enzymes in the lumen, as well as the presence of a membrane protein that transports ATP across the thylakoid membrane into the lumen [Spetea et al. (2004) Proc. Natl. Acad. Sci. USA. 101:1409-1414]. The transporter belongs to the mitochondrial carrier family and has the working name Thylakoid Nucleotide Carrier (TNC). Homology searches with the sequence of the mitochondrial ATP/ADP carrier in the Arabidopsis database combined with prediction for chloroplast transit peptides revealed one protein as a likely candidate for TNC. The endogenous TNC protein has been detected in thylakoid membrane fractions of A. thaliana by specific antibodies. Topology studies have shown that it is an integral membrane protein. Transport of ATP across the membrane readily occurs in the dark and is stimulated by the light-dependent electron transport. The pH component of the proton motif force is most likely the driving force for transport. Knock-out plants lacking the putative TNC (shown on protein level by specific antibodies) are growing and will be tested for transport of nucleotides across the thylakoid membrane.

KEY WORDS: ATP transport, thylakoid membrane, mitochondrial carrier