An ELIP-like gene in the freshwater green alga, Spirogyra varians (Zygnematales), is regulated by cold stress and CO2 influx

A cold-stress responsive protein was isolated from the freshwater alga Spirogyra varians and named SVCR1 (S. varians cold responsive protein). The protein was detected by comparing the protein profiles of plants grown at two different temperatures, 4 A degrees C and 20 A degrees C. Two-dimensional gel electrophoresis (2-DE) showed that expression of the protein was reversibly regulated by cold stress. The full cDNA sequence of the protein was obtained using degenerate primers. The deduced amino acid sequence showed high similarity with early light-inducible proteins (ELIPs), a group of nuclear-encoded chloroplast proteins that are induced by high light stress in higher plants. The expression of svcr1 (S. varians cold responsive gene) responded more sensitively to cold than to high light. At temperatures over 10 A degrees C, svcr1 was seldom expressed until light intensity reached 1,200 mu mol photons m(-2) s(-1). At 4 A degrees C, it was greatly up-regulated even in the dark. A sharp increase of svcr1 expression was observed when the algae were exposed to UV-A light for 1 h regardless of temperature. The addition of 5 % CO2 to the algal culture medium suppressed the expression of svcr1. The transcripts of svcr1 began to disappear as soon as 5 % CO2 was introduced to plants grown in the cold. The photosynthetic efficiency (F (v)/F (m) and non-photochemical quenching induction) was measured at 4 A degrees C and 20 A degrees C using PAM. The decreased photosynthetic efficiency at 4 A degrees C was recovered close to that of 20 A degrees C when the 5 % CO2 was provided. These results suggest that the elevated carbon level in the solution may mitigate oxidative stress in photosystem caused by cold stress. The recovered photosynthetic efficiency with CO2 influx at 4 A degrees C supported this hypothesis.