▪ Abstract Plant responses to salinity stress are reviewed with emphasis on molecular mechanisms of signal transduction and on the physiological consequences of altered gene expression that affect biochemical reactions downstream of stress sensing. We make extensive use of comparisons with model organisms, halophytic plants, and yeast, which provide a paradigm for many responses to salinity exhibited by stress-sensitive plants. Among biochemical responses, we emphasize osmolyte biosynthesis and function, water flux control, and membrane transport of ions for maintenance and re-establishment of homeostasis. The advances in understanding the effectiveness of stress responses, and distinctions between pathology and adaptive advantage, are increasingly based on transgenic plant and mutant analyses, in particular the analysis of Arabidopsis mutants defective in elements of stress signal transduction pathways. We summarize evidence for plant stress signaling systems, some of which have components analogous to t...

Plant cellular and molecular responses to high salinity.

Plant salt tolerance

The onset of M-phase is regulated by a mechanism common to all eukaryotic cells. Entry into M-phase is determined by activation of the p34cdc2 protein kinase which requires p34cdc2 dephosphorylation and association with cyclin.

Universal control mechanism regulating onset of M-phase

Alternative pre-mRNA splicing is a central mode of genetic regulation in higher eukaryotes. Variability in splicing patterns is a major source of protein diversity from the genome. In this review, I describe what is currently known of the molecular mechanisms that control changes in splice site choice. I start with the best-characterized systems from the Drosophila sex determination pathway, and then describe the regulators of other systems about whose mechanisms there is some data. How these regulators are combined into complex systems of tissue-specific splicing is discussed. In conclusion, very recent studies are presented that point to new directions for understanding alternative splicing and its mechanisms.

/pdf/mechanisms-of-alternative-pre-messenger-rna-splicing-3d5lzfbjvj.pdf

Mechanisms of Alternative Pre-Messenger RNA Splicing

The identification of untranslated regions, introns, and coding regions within an organism remains challenging. We developed a quantitative sequencing-based method called RNA-Seq for mapping transcribed regions, in which complementary DNA fragments are subjected to high-throughput sequencing and mapped to the genome. We applied RNA-Seq to generate a high-resolution transcriptome map of the yeast genome and demonstrated that most (74.5%) of the nonrepetitive sequence of the yeast genome is transcribed. We confirmed many known and predicted introns and demonstrated that others are not actively used. Alternative initiation codons and upstream open reading frames also were identified for many yeast genes. We also found unexpected 3'-end heterogeneity and the presence of many overlapping genes. These results indicate that the yeast transcriptome is more complex than previously appreciated.

/pdf/the-transcriptional-landscape-of-the-yeast-genome-defined-by-p354u8wkq4.pdf

The Transcriptional Landscape of the Yeast Genome Defined by RNA Sequencing

Mapping Pathways and Phenotypes by Systematic Gene Overexpression

Calcineurin is a conserved Ca^(2+)/calmodulin-dependent protein phosphatase that plays a critical role in Ca^(2+) signaling. We describe new components of a calcineurin-mediated response in yeast, the Ca^(2+)-induced transcriptional activation ofFKS2, which encodes a β-1,3 glucan synthase. A 24-bp region of the FKS2 promoter was defined as sufficient to confer calcineurin-dependent transcriptional induction on a minimal promoter in response to Ca^(2+) and was named CDRE (forcalcineurin-dependentresponse element). The product ofCRZ1 (YNL027w) was identified as an activator of CDRE-driven transcription. Crz1p contains zinc finger motifs and binds specifically to the CDRE. Genetic analysis revealed that crz1Δ mutant cells exhibit several phenotypes similar to those of calcineurin mutants and that overexpression of CRZ1 in calcineurin mutants suppressed these phenotypes. These results suggest that Crz1p functions downstream of calcineurin to effect multiple calcineurin-dependent responses. Moreover, the calcineurin-dependent transcriptional induction of FKS2 in response to Ca^(2+), α-factor, and Na^+ was found to require CRZ1. In addition, we found that the calcineurin-dependent transcriptional regulation ofPMR2 and PMC1 required CRZ1. However, transcription of PMR2 and PMC1 was activated by only a subset of the treatments that activated FKS2 transcription. Thus, in response to multiple signals, calcineurin acts through the Crz1p transcription factor to differentially regulate the expression of several target genes in yeast.

/pdf/calcineurin-acts-through-the-crz1-tcn1-encoded-transcription-438rp1j8wf.pdf

Calcineurin acts through the CRZ1/TCN1-encoded transcription factor to regulate gene expression in yeast

http://www.jbc.org/content/277/34/31079.full.pdf

Genome-wide Analysis of Gene Expression Regulated by the Calcineurin/Crz1p Signaling Pathway in Saccharomyces cerevisiae

Calcineurin signaling in Saccharomyces cerevisiae: how yeast go crazy in response to stress

Calcium ions, present inside all eukaryotic cells, are important second messengers in the transduction of biological signals. In mammalian cells, the release of Ca2+ from intracellular compartments is required for signaling and involves the regulated opening of ryanodine and inositol-1,4,5-trisphosphate (IP3) receptors. However, in budding yeast, no signaling pathway has been shown to involve Ca2+ release from internal stores, and no homologues of ryanodine or IP3 receptors exist in the genome. Here we show that hyperosmotic shock provokes a transient increase in cytosolic Ca2+ in vivo. Vacuolar Ca2+, which is the major intracellular Ca2+ store in yeast, is required for this response, whereas extracellular Ca2+ is not. We aimed to identify the channel responsible for this regulated vacuolar Ca2+ release. Here we report that Yvc1p, a vacuolar membrane protein with homology to transient receptor potential (TRP) channels, mediates the hyperosmolarity induced Ca2+ release. After this release, low cytosolic Ca2+ is restored and vacuolar Ca2+ is replenished through the activity of Vcx1p, a Ca2+/H+ exchanger. These studies reveal a novel mechanism of internal Ca2+ release and establish a new function for TRP channels.

/pdf/internal-ca2-release-in-yeast-is-triggered-by-hypertonic-3w7wld2fl0.pdf

Martha S. Cyert

Papers

Mapping Pathways and Phenotypes by Systematic Gene Overexpression

Calcineurin acts through the CRZ1/TCN1-encoded transcription factor to regulate gene expression in yeast

Genome-wide Analysis of Gene Expression Regulated by the Calcineurin/Crz1p Signaling Pathway in Saccharomyces cerevisiae

Calcineurin signaling in Saccharomyces cerevisiae: how yeast go crazy in response to stress

Internal Ca2+ release in yeast is triggered by hypertonic shock and mediated by a TRP channel homologue