Identification of the catalase gene promoter region involved in superinduction in Schizosaccharomyces pombe caused by cycloheximide and hydrogen peroxide

Cycloheximide-mediated superinduction of genes involves both native and foreign transcripts in rice (Oryza sativa L.)

Rice seedlings subjected to heat shock show rapid and transient induction of Oshsp17.4-CI, Oshsp17.9A-CI and OsClpB-cyt/hsp100 transcripts. When the seedlings were pre-treated with protein synthesis inhibitor cycloheximide, levels of the above transcripts during heat shock were more elevated than those seen with heat shock alone. Heat stress and cycloheximide co-treatment resulted in higher transcript accumulation in comparison to cycloheximide pre-treatment followed by heat stress. In transgenic plants raised with OsClpB-cyt/hsp100 promoter driving expression of the reporter gus gene, expression of the gus transcript was subjected to similar superinduction event as was seen with native OsClpB-cyt/hsp100 transcripts in untransformed plants. Yeast cells transformed with variably-sized rice ClpB-cyt/hsp100 promoter driving expression of the lacZ reporter transcript showed that specific sequences of the promoter region may be implicated in superinduction.

Osmotic stress signaling and osmoadaptation in yeasts

The ability to adapt to altered availability of free water is a fundamental property of living cells. The principles underlying osmoadaptation are well conserved. The yeast Saccharomyces cerevisiae is an excellent model system with which to study the molecular biology and physiology of osmoadaptation. Upon a shift to high osmolarity, yeast cells rapidly stimulate a mitogen-activated protein (MAP) kinase cascade, the high-osmolarity glycerol (HOG) pathway, which orchestrates part of the transcriptional response. The dynamic operation of the HOG pathway has been well studied, and similar osmosensing pathways exist in other eukaryotes. Protein kinase A, which seems to mediate a response to diverse stress conditions, is also involved in the transcriptional response program. Expression changes after a shift to high osmolarity aim at adjusting metabolism and the production of cellular protectants. Accumulation of the osmolyte glycerol, which is also controlled by altering transmembrane glycerol transport, is of central importance. Upon a shift from high to low osmolarity, yeast cells stimulate a different MAP kinase cascade, the cell integrity pathway. The transcriptional program upon hypo-osmotic shock seems to aim at adjusting cell surface properties. Rapid export of glycerol is an important event in adaptation to low osmolarity. Osmoadaptation, adjustment of cell surface properties, and the control of cell morphogenesis, growth, and proliferation are highly coordinated processes. The Skn7p response regulator may be involved in coordinating these events. An integrated understanding of osmoadaptation requires not only knowledge of the function of many uncharacterized genes but also further insight into the time line of events, their interdependence, their dynamics, and their spatial organization as well as the importance of subtle effects.