Plant Physiol, May 2000, Vol. 123, pp. 215-222
The BtpA Protein Stabilizes the Reaction Center Proteins of
Photosystem I in the Cyanobacterium Synechocystis sp. PCC
6803 at Low Temperature1
Elena
Zak and
Himadri B.
Pakrasi*
Department of Biology, Washington University, St. Louis, Missouri
63130
Specific inhibition of photosystem I (PSI) was observed under
low-temperature conditions in the cyanobacterium
Synechocystis sp. strain PCC 6803. Growth at 20°C
caused inhibition of PSI activity and increased degradation of the PSI
reaction center proteins PsaA and PsaB, while no significant changes
were found in the level and activity of photosystem II (PSII). BtpA, a
recently identified extrinsic thylakoid membrane protein, was found to be a necessary regulatory factor for stabilization of the PsaA and PsaB
proteins under such low-temperature conditions. At normal growth
temperature (30°C), the BtpA protein was present in the cell, and its
genetic deletion caused an increase in the degradation of the PSI
reaction center proteins. However, growth of
Synechocystis cells at 20°C or shifting of cultures
grown at 30°C to 20°C led to a rapid accumulation of the BtpA
protein, presumably to stabilize the PSI complex, by lowering the rates
of degradation of the PsaA and PsaB proteins. A btpA
deletion mutant strain could not grow photoautotrophically at low
temperature, and exhibited rapid degradation of the PSI complex after
transfer of the cells from normal to low temperature.
1
This work was supported by grants from the
National Science Foundation (no. MCB 96-32162) and the International
Human Frontier Science Program (to H.B.P.).
*
Corresponding author; e-mail Pakrasi{at}biology.wustl.edu; fax
314-935-6803.
© 2000 American Society of Plant Physiologists
