Expression of one of the members of the Arabidopsis chaperonin 60 beta gene family is developmentally regulated and wound-repressible

The complexity of chloroplast chaperonins

Type I chaperonins are large oligomeric protein ensembles that are involved in the folding and assembly of other proteins. Chloroplast chaperonins and co-chaperonins exist in multiple copies of two distinct isoforms that can combine to form a range of labile oligomeric structures. This complex system increases the potential number of chaperonin substrates and possibilities for regulation. The incorporation of unique subunits into the oligomer can modify substrate specificity. Some subunits are upregulated in response to heat shock and some show organ-specific expression, whereas others possess additional functions that are unrelated to their role in protein folding. Accumulating evidence suggests that specific subunits have distinct roles in biogenesis of ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco).

Comparative proteomic analysis of the short-term responses of rice roots and leaves to cadmium

Cadmium (Cd) is a non-essential heavy metal that is recognized as a major environmental pollutant. While Cd responses and toxicities in some plant species have been well established, there are few reports about the effects of short-term exposure to Cd on rice, a model monocotyledonous plant, at the proteome level. To investigate the effect of Cd in rice, we monitored the influence of Cd exposure on root and leaf proteomes. After Cd treatment, root and leaf tissues were separately collected and leaf proteins were fractionated with polyethylene glycol. Differentially regulated proteins were selected after image analysis and identified using MALDI-TOF MS. A total of 36 proteins were up- or down-regulated following Cd treatment. As expected, total glutathione levels were significantly decreased in Cd-treated roots, and approximately half of the up-regulated proteins in roots were involved in responses to oxidative stress. These results suggested that prompt antioxidative responses might be necessary for the reduction of Cd-induced oxidative stress in roots but not in leaves. In addition, RNA gel blot analysis showed that the proteins identified in the proteomic analysis were also differentially regulated at the transcriptional level. Collectively, our study provides insights into the integrated molecular mechanisms of early responses to Cd in rice.

Regulation of isoprene synthase promoter by environmental and internal factors

Isoprene synthase (ISPS) catalyzes the formation of isoprene, an important volatile terpenoid with strong effects on global atmospheric chemistry and protective physiological functions in plant leaves. Many terpene synthase genes including isoprene synthase, a member of the TPS-b cluster of this numerous gene family, were already functionally analysed but much less is known about regulation of their promoters. To study regulation of the PcISPS gene in detail we developed transgenic Grey poplar (Populus x canescens) and Arabidopsis thaliana plants in which the PcISPS promoter is fused to enhanced green fluorescent protein (E-GFP) and beta-glucuronidase (GUS) reporter genes. We analysed these reporters during plant development, for organ specificity and in plants subjected to different light and temperature regimes. We observed low promoter activity in non-isoprene emitting tissue like roots where ISPS gene is transcribed but no active enzyme is detectable. In leaves we demonstrate that light and temperature directly modulate ISPS promoter activity. Moreover, with confocal laser scanning microscopy we show a cell specific gradient of ISPS promoter activity within the leaf parenchyma depending on light direction. Our results indicate that ISPS promoter activity, which correlates with basal isoprene emission capacity, is not uniformly distributed within leaf tissue and that it can adapt rapidly towards internal as well as external environmental stimuli.

Arabidopsis thaliana type I and II chaperonins

An examination of the Arabidopsis thaliana genome sequence led to the identification of 29 predicted genes with the potential to encode members of the chaperonin family of chaperones (CPN60 and CCT), their associated cochaperonins, and the cytoplasmic chaperonin cofactor prefoldin. These comprise the first complete set of plant chaperonin protein sequences and indicate that the CPN family is more diverse than previously described. In addition to surprising sequence diversity within CPN subclasses, the genomic data also suggest the existence of previously undescribed family members, including a 10-kDa chloroplast cochaperonin. Consideration of the sequence data described in this review prompts questions about the complexities of plant CPN systems and the evolutionary relationships and functions of the component proteins, most of which have not been studied experimentally.

Chlamydomonas transcripts encoding three divergent plastid chaperonins are heat-inducible

Three cDNAs encoding plastid cpn60 chaperonin subunits have been isolated from the unicellular green alga Chlamydomonas reinhardtii. Based on comparisons of the predicted amino acid sequences, we conclude that Chlamydomonas, like higher plants, contains divergent plastid cpn60-alpha and cpn60-beta subunits. The predicted amino acid sequences of the two Chlamydomonas cpn60-beta subunits differ significantly (24% divergent), indicating that the two cpn60-beta subunits have been selectively maintained for a considerable period of time. Unlike plastid chaperonin transcripts in higher plants, heat shock conditions (42 degrees C) lead to a rapid increase (10- to 30-fold) in the level of each of the three plastid transcripts.