We performed genome-wide expression analysis to determine genetic responses in Saccharomyces cerevisiae to a low temperature environment using a cDNA microarray. Approximately 25% of the genes in the yeast genome were found to be involved in the response of yeast to low temperature. This finding of a large number of genes being involved in the response to low temperature enabled us to give a functional interpretation to the genetic responses to the stimulus. Functional and clustering analyses of temporal changes in gene expression revealed that global states of the expressions of up-regulated genes could be characterized as having three phases (the early, middle, and late phases). In each phase, genes related to rRNA synthesis, ribosomal proteins, or several stress responses are time-dependently up-regulated, respectively. Through these phases, yeast cells may improve reduced efficiency of translation and enhance cell protection mechanisms to survive under a low temperature condition. Furthermore, these time-dependent regulations of these genes would be controlled by the cAMP-protein kinase A pathway. The results of our study provide a global description of transcriptional response for adaptation to low temperature in yeast cells.Low temperatures are known to have several effects on biochemical and physiological properties in various cells (e.g. low efficiency of protein translation, low fluidity of cellular membrane, stabilization of double helix or secondary structure of DNA or RNA molecule, slow folding of protein, and decrease of enzymatic activities) (1-3). Most organisms would have developed adaptive mechanisms to cope with these phenomena. The mechanisms underlying low temperature-dependent gene expression and responses to low temperature have been studied in few organisms (4 -6).In prokaryotes, especially Escherichia coli, when cells grown at 37°C are exposed to a low temperature, such as 15°C, a set of proteins called cold shock proteins are transiently induced (7). CspA has been identified as a major cold shock protein (8) and has been suggested to act as an RNA chaperone to increase efficiency of translation under a low temperature condition (9). It has been reported that Bacillus and Synechococcus species increase synthesis and stability of desaturases, which catalyze unsaturation of fatty acids in the membrane phopholipids under a low temperature condition (4, 10). Induction of desaturases by low temperature has also been found in eukaryotic species, such as plants (5, 6), protozoan (12), dimorphic fungus (13), fish (14), and yeast (15). These findings suggest that cellular responses to low temperature, such as improvement of reduced translation and decreased membrane fluidity, and their mechanisms are common in various organisms.In yeast, Saccharomyces cerevisiae, several cold-inducible genes have been identified. NSR1, one of the cold-inducible genes, encodes a nucleolin-like protein related to rRNA processing and ribosomal biosynthesis (16 -18). TIP1 (temperatureinducible protein) and the other m...

eThe vertical transmission of symbiotic microorganisms is omnipresent in insects, while the evolutionary process remains totally unclear. The oriental chinch bug, Cavelerius saccharivorus (Heteroptera: Blissidae), is a serious sugarcane pest, in which symbiotic bacteria densely populate the lumen of the numerous tubule-like midgut crypts that the chinch bug develops. Cloning and sequence analyses of the 16S rRNA genes revealed that the crypts were dominated by a specific group of bacteria belonging to the genus Burkholderia of the Betaproteobacteria. The Burkholderia sequences were distributed into three distinct clades: the Burkholderia cepacia complex (BCC), the plant-associated beneficial and environmental (PBE) group, and the stinkbug-associated beneficial and environmental group (SBE). Diagnostic PCR revealed that only one of the three groups of Burkholderia was present in ϳ89% of the chinch bug field populations tested, while infections with multiple Burkholderia groups within one insect were observed in only ϳ10%. Deep sequencing of the 16S rRNA gene confirmed that the Burkholderia bacteria specifically colonized the crypts and were dominated by one of three Burkholderia groups. The lack of phylogenetic congruence between the symbiont and the host population strongly suggested host-symbiont promiscuity, which is probably caused by environmental acquisition of the symbionts by some hosts. Meanwhile, inspections of eggs and hatchlings by diagnostic PCR and egg surface sterilization demonstrated that almost 30% of the hatchlings vertically acquire symbiotic Burkholderia via symbiont-contaminated egg surfaces. The mixed strategy of symbiont transmission found in the oriental chinch bug might be an intermediate stage in evolution from environmental acquisition to strict vertical transmission in insects.

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The psychrophilic fungi Coprinus psychromorbidus and Typhula ishikariensis produced unique antifreeze proteins (AFPs) in the extracellular space. Molecular masses of purified fungal AFPs of C. psychromorbidus and T. ishikariensis were approximately 22 and 23 kDa, respectively. Cloned genes of AFPs from T. ishikariensis do not have any similarity with known proteins. Purified fungal AFPs from cultural filtrate of T. ishikariensis and recombinant fungal AFP from methylotrophic yeast formed specific ice crystals resembling "Stone Age knives". These observations indicate that fungal AFPs do not form proper hexagonal ice crystals to inhibit their growth and that fungal AFPs can probably bind to surfaces of ice crystals in an irregular manner.Key words: antifreeze protein, snow mold fungi, Coprinus psychromorbidus, Typhula ishikariensis.