Complexity of Hsp90 in organelle targeting
ABSTRACT Heat shock protein 90 (Hsp90) is an abundant and highly conserved molecular chaperone. In Arabidopsis, the Hsp90 gene family consists of seven members. Here, we report that the AtHsp90-6 gene gives rise to two mRNA populations, termed AtHsp90-6L and AtHsp90-6S due to alternative initiation of transcription. The AtHsp90-6L and AtHsp90-6S transcription start sites are located 228 nucleotides upstream and 124 nucleotides downstream of the annotated translation start site, respectively. Both transcripts are detected under normal or heat-shock conditions. The inducibility of AtHsp90-6 mRNAs by heat shock implies a potential role of both isoforms in stress management. Stable transformation experiments with fusion constructs between the N-terminal part of each AtHsp90-6 isoform and green fluorescent protein indicated import of both fusion proteins into mitochondria. In planta investigation confirmed that fusion of the AtHsp90-5 N-terminus to green fluorescent protein (GFP) did result in specific chloroplastic localization. The mechanisms of regulation for mitochondria- and plastid-localized chaperone-encoding genes are not well understood. Future work is needed to address the possible roles of harsh environmental conditions and developmental processes on fine-tuning and compartmentalization of the AtHsp90-6L, AtHsp90-6S, and AtHsp90-5 proteins in Arabidopsis.
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ABSTRACT: Heat shock protein 90 (HSP90), a highly conserved molecular chaperone, plays essential roles in folding, keeping structural integrity, and regulating the subset of cytosolic proteins. We cloned the cDNA of Chlorella vulgaris HSP90 (named CvHSP90) by combining homology cloning with rapid amplification of cDNA ends (RACE). Sequence analysis indicated that CvHSP90 is a cytosolic member of the HSP90 family. Quantitative RT-PCR was applied to determine the expression level of messenger RNA (mRNA) in CvHSP90 under different stress conditions. C. vulgaris was kept in different temperatures (5-45°C) for 1 h. The mRNA expression level of CvHSP90 increased with temperature from 5 to 10°C, went further from 35 to 40°C, and reached the maximum at 40°C. On the other hand, for C. vulgaris kept at 35°C for different durations, the mRNA expression level of CvHSP90 increased gradually and reached the peak at 7 h and then declined progressively. In addition, the expression level of CvHSP90 at 40 or 45 in salinity (‰) was almost fourfold of that at 25 in salinity (‰) for 2 h. Therefore, CvHSP90 may be a potential biomarker to monitor environment changes.03/2014; 2014:487050. DOI:10.1155/2014/487050
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ABSTRACT: Plant roots play an important role in uptake of water and nutrients, support of above-ground part and environmental sensing, but the molecular mechanisms underlying the root development are poorly understood in rice. We found that a gene (OsASL1) encoding argininosuccinate lyase is involved in normal root development of rice. OsASL1 cleaves argininosuccinate to arginine and fumarate reversibly, the last step in the arginine biosynthetic pathway. Here, we further characterized OsASL1 in terms of expression pattern, subcellular localization, and arginine effect on the root growth. A detailed expression analysis revealed that 2 transcripts of OsASL1, OsASL1.1 and OsASL1.2, showed different expression patterns; OsASL1.1 was expressed in most organs throughout the whole growth period, whereas OsASL1.2 was mainly expressed in the roots. In contrast to plastid-localized OsASL1.1, OsASL1.2 was localized to the cytosol and nucleus. The short-root phenotype of the mutant was not rescued by exogenous addition of the sodium nitroprusside, a nitric oxide donor, but rescued by an appropriate concentration of Arg. Our results indicate that the subcellular localization was determined by the N terminus of OsASL1 and that appropriate concentration of Arg is required for normal root elongation in rice.Plant signaling & behavior 04/2014; 9(3). DOI:10.4161/psb.28717
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ABSTRACT: Background and Aims: Heat shock protein 90 (Hsp90) proteins constitute an important gene family of molecular chaperons. High-temperature stress, which is often combined with drought stress, may exert major constraints to grapevine growth and development. The aim of this study was to characterise the Vitis vinifera Hsp90 gene family.Methods and Results: Using the complete grapevine genome sequences, four cytoplasmic and three organelle-specific V. vinifera Hsp90 (VvHsp90) proteins were identified. Phylogenetic analysis revealed that they share high sequence similarity with their Arabidopsis counterparts, while the cytosolic isoforms are clustered into two distinct groups (VvHsp90.1 and VvHsp90.2). Transcriptional analysis showed that a representative gene from the first group (VvHsp90.1a), in contrast to VvHsp90.2a, is induced by heat shock in all vegetative tissues/organs tested. Interestingly, it was also expressed in tendrils in the absence of stress. The severity and duration of heat stress influenced in a complex manner the expression profile of VvHsp90.1a, while the other VvHsp90s tested were rather constitutively regulated. However, the endoplasmic reticulum-specific VvHsp90.7 was mildly and transiently induced by a relatively prolonged heat stress. Combined drought with heat stress resulted in a delay in VvHsp90.1a induction.Conclusions: Gene structure organisation and expression characteristics of VvHsp90s resemble those of their Arabidopsis orthologs, although species-specific differences also exist. Differential regulation of genes suggests functional diversification among isoforms.Significance of the Study: This is the first report on the characterisation of Hsp90s in grapevine. The present study contributes to a deeper understanding of the complex molecular responses of grapevine to stress.Australian Journal of Grape and Wine Research 02/2012; 18(1). DOI:10.1111/j.1755-0238.2011.00166.x · 2.78 Impact Factor