The Role Of RNA-binding Protein Gene Rbp3 In Cold Acclimation Of The Cyanobacterium Synechocystis Sp. Strain PCC6803

Synechocystis sp. PCC6803, a unicellular cyanobacterium, is able to grow both photoautotrophically on CO2 and heterotrophically on glucose, and naturally transformable by exogenous DNA. It is one of the model species used in studies of the biology of cyanobacteria. As a unicellular mesophillic cyanobacterium, it grows in a range of favorable temperature from 25 to 40℃with optimal growth temperature at 30℃. In this study, transcriptional profiles at 15℃were analyzed using DNA microarrays, and the RNA-binding protein gene rpb3 was investigated for its role in cold acclimation.The experimentation and results are described in two parts:(1) Genome-wide transcriptional analyses of Synechocystis sp. PCC6803. Using DNA microarrays, differences of genome-wide transcriptional profiles were analyzed in cells grown at 30℃and treated at 15℃. At 15oC in the light, 282 out of 2950 genes were up-regulated compared with 30oC, and 223 genes down-regulated. At 15oC in the dark, 154 genes were up-regulated compared with 30oC, and 212 genes down-regulated. Among these genes, 25 were up-regulated at 15oC both in the light and dark compared with 30oC, including 16 genes of known functions and 9 genes of unknown functions. These genes encode proteins involved in transcription, translation, electron transfer and photosystems. We also identified 49 genes that were down-regulated by temperature down-shift both in the light and in the dark. These genes are involved in photosynthesis, protein folding and so on.(2) The role of rpb3 in cold acclimation. There is no difference in the growth of rbp3::? mutant and WT at 30oC and 15oC. However, the low temperature enhancement percentage of rbp3::? mutant is 41.6±4.2, which suggests that rbp3 plays an important role in chill-light tolerance. Because the unsaturation degree of membrane fatty acids is an important factor involved in cold acclimation of Synechocystis sp. PCC6803, we analyzed the expression of fatty acid desaturase genes desA, desB and desD and fatty acid compositions in the rbp3::? mutant and the wild type. The expression of fatty acid desaturase genes and the unsaturation degree of fatty acids are both remarkably decreased in the rbp3 mutant. rbp3 is transcribed as a monocistron and slightly up-regulated by low temperature.The main conclusions of this study are as follows:(1) rbp3 plays an important role in cold acclimation in Synechocystis sp. PCC6803;(2) rbp3 is transcribed as a monocistron and slightly up-regulated by low temperature;(3) rbp3 greatly influences the expression level of desA, desB and desD.