Dataset Information

Small chloroplast-targeted DnaJ proteins are involved in optimization of photosynthetic reactions in Arabidopsis thaliana.

ABSTRACT:

Background

DnaJ proteins participate in many metabolic pathways through dynamic interactions with various components of these processes. The role of three small chloroplast-targeted DnaJ proteins, AtJ8 (At1 g80920), AtJ11 (At4 g36040) and AtJ20 (At4 g13830), was investigated here using knock-out mutants of Arabidopsis thaliana. Photochemical efficiency, capacity of CO2 assimilation, stabilization of Photosystem (PS) II dimers and supercomplexes under high light illumination, energy distribution between PSI and PSII and phosphorylation of PSII-LHCII proteins, global gene expression profiles and oxidative stress responses of these DnaJ mutants were analyzed.

Results

Knockout of one of these proteins caused a series of events including a decrease in photosynthetic efficiency, destabilization of PSII complexes and loss of control for balancing the redox reactions in chloroplasts. Data obtained with DNA microarray analysis demonstrated that the lack of one of these DnaJ proteins triggers a global stress response and therefore confers the plants greater tolerance to oxidative stress induced by high light or methyl viologen treatments. Expression of a set of genes encoding enzymes that detoxify reactive oxygen species (ROS) as well as a number of stress-related transcription factors behaved in the mutants at growth light similarly to that when wild-type (WT) plants were transferred to high light. Also a set of genes related to redox regulation were upregulated in the mutants. On the other hand, although the three DnaJ proteins reside in chloroplasts, the expression of most genes encoding thylakoid membrane proteins was not changed in the mutants.

Conclusion

It is proposed that the tolerance of the DnaJ protein knockout plants to oxidative stress occurs at the expense of the flexibility of photosynthetic reactions. Despite the fact that the effects of the individual protein knockout on the response of plants to high light treatment are quite similar, it is conceivable that both specific- and cross-talk functions exist between the three small chloroplast-targeted DnaJ proteins, AtJ8, AtJ11 and AtJ20.

SUBMITTER: Chen KM

PROVIDER: S-EPMC2844072 | biostudies-literature | 2010 Mar

REPOSITORIES: biostudies-literature

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Publications

Small chloroplast-targeted DnaJ proteins are involved in optimization of photosynthetic reactions in Arabidopsis thaliana.

Chen Kun-Ming KM Holmström Maija M Raksajit Wuttinun W Suorsa Marjaana M Piippo Mirva M Aro Eva-Mari EM

BMC plant biology 20100307

<h4>Background</h4>DnaJ proteins participate in many metabolic pathways through dynamic interactions with various components of these processes. The role of three small chloroplast-targeted DnaJ proteins, AtJ8 (At1 g80920), AtJ11 (At4 g36040) and AtJ20 (At4 g13830), was investigated here using knock-out mutants of Arabidopsis thaliana. Photochemical efficiency, capacity of CO2 assimilation, stabilization of Photosystem (PS) II dimers and supercomplexes under high light illumination, energy distr ...[more]

PMID: 20205940

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Project description:Glucosinolates are plant secondary metabolites present in Brassicaceae plants such as the model plant Arabidopsis thaliana. Intact glucosinolates are believed to be biologically inactive, whereas degradation products after hydrolysis have multiple roles in growth regulation and defense. The degradation of glucosinolates is catalyzed by thioglucosidases called myrosinases and leads by default to the formation of isothiocyanates. The interaction of a protein called epithiospecifier protein (ESP) with myrosinase diverts the reaction toward the production of epithionitriles or nitriles depending on the glucosinolate structure. Here we report the identification of a new group of nitrile-specifier proteins (AtNSPs) in A. thaliana able to generate nitriles in conjunction with myrosinase and a more detailed characterization of one member (AtNSP2). Recombinant AtNSP2 expressed in Escherichia coli was used to test its impact on the outcome of glucosinolate hydrolysis using a gas chromatography-mass spectrometry approach. AtNSP proteins share 30-45% sequence homology with A. thaliana ESP. Although AtESP and AtNSP proteins can switch myrosinase-catalyzed degradation of 2-propenylglucosinolate from isothiocyanate to nitrile, only AtESP generates the corresponding epithionitrile. Using the aromatic benzylglucosinolate, recombinant AtNSP2 is also able to direct product formation to the nitrile. Analysis of glucosinolate hydrolysis profiles of transgenic A. thaliana plants overexpressing AtNSP2 confirms its nitrile-specifier activity in planta. In silico expression analysis reveals distinctive expression patterns of AtNSPs, which supports a biological role for these proteins. In conclusion, we show that AtNSPs belonging to a new family of A. thaliana proteins structurally related to AtESP divert product formation from myrosinase-catalyzed glucosinolate hydrolysis and, thereby, likely affect the biological consequences of glucosinolate degradation. We discuss similarities and properties of AtNSPs and related proteins and the biological implications.

Dataset Information

Small chloroplast-targeted DnaJ proteins are involved in optimization of photosynthetic reactions in Arabidopsis thaliana.

Background

Results

Conclusion

Publications

Small chloroplast-targeted DnaJ proteins are involved in optimization of photosynthetic reactions in Arabidopsis thaliana.

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