Plant and Cell Physiology, 2002, Vol. 43, No. 2 217-223
© 2002 Oxford University Press
A High Temperature-Sensitive Mutant of Synechococcus sp. PCC 7002 with Modifications in the Endogenous Plasmid, pAQ1
1 Graduate School of Science and Engineering, Ehime University, Matsuyama, Ehime, 790-8577 Japan 2 Department of Chemistry, Faculty of Science, Ehime University, Matsuyama, Ehime, 790-8577 Japan 3 Satellite Venture Business Laboratory, Ehime University, Matsuyama, Ehime, 790-8577 Japan
To study thermal adaptations in the cyanobacterium, Synechococcus sp. PCC 7002, we screened about 3,000 mutants for their tolerance to high temperature, and found one, SHT1, that is sensitive to high-temperature stress. The mutant had a modified gene construct in the endogenous plasmid, pAQ1. One of the four ORFs, ORF93, was duplicated, and its mRNA level was higher than in the wild type. At 38°C, the growth of SHT1 was retarded as compared with the wild type, and above 38°C, almost all the cells of SHT1 died. This temperature is much lower than that required for induction of heat shock proteins. Interestingly, in both the wild type and SHT1, the thermal stability of oxygen-evolving machinery increased upon acclimation to high temperatures. These findings indicate that the lack of thermal tolerance in the SHT1 strain is likely independent of the adaptation of the PSII complex and heat shock responses, whereas there are essential contributions of genes in the endogenous plasmid to the adaptation to high temperature. Thus, understanding the role of pAQ1 in the adaptation of Synechococcus sp. PCC 7002 to high-temperature environments is the first step in elucidating the function of this plasmid.
4 Present address: Center for Gene Research, Ehime University, Matsuyama, Ehime, 790-8566 Japan.
5 Corresponding author: E-mail, hhayashi@dpc.ehime-u.ac.jp; Fax, +81-89-927-9611.