Rubisco Binding Protein Research Articles

Drought stress response in winter wheat varieties – changes in leaf proteins and proteolytic activities

Radiation mutagenesis has been used in sustainable agriculture as a tool for increasing plant variability and providing new lines for selection. This necessitates a comparison, by using suitable stress markers, of the newly created lines with some well-established varieties, which are stress tolerant or susceptible. Drought is one of the most frequently encountered stresses with deleterious effects on plant performance and crop yield. Winter wheat seedlings (soil cultures at 3–4th leaf stage) from one mutant line (M181/1338K), one drought-tolerant (Guinness) and one sensitive variety (Farmer) were subjected to severe drought stress by water withholding, followed by recovery. Changes in leaf protein profiles, the amount of Rubisco large subunit (RLS), some specific chloroplast proteins such as Rubisco binding protein (RPB), Rubisco activase (RA), the chaperone subunit clpA/C of clp protease, as well as the activities of exo- and endo-proteases were analyzed. At the protein level, some differences were found in the drought response of genotypes – stability of RLS and RBP in M181/1338K and Guinness, diminution of RLS and increase in RBP in Farmer. RA presented strong up-regulation at recovery in Guinness but decreased in content under drought in M181/1338K and Farmer. Increase in ClpA/C level was found in all compared varieties under stress. Strong increase in total proteolytic activity was detected under drought only in Farmer. Inhibitory analysis revealed a predominance of cysteine and serine protease types. Aminopeptidase activities remained higher at recovery in M181/1338K and Farmer. Results are discussed in terms of genotype-linked different stress coping strategies.

A Rubisco-binding protein is required for normal pyrenoid number and starch sheath morphology in Chlamydomonas reinhardtii

A phase-separated, liquid-like organelle called the pyrenoid mediates CO2 fixation in the chloroplasts of nearly all eukaryotic algae. While most algae have 1 pyrenoid per chloroplast, here we describe a mutant in the model alga Chlamydomonas that has on average 10 pyrenoids per chloroplast. Characterization of the mutant leads us to propose a model where multiple pyrenoids are favored by an increase in the surface area of the starch sheath that surrounds and binds to the liquid-like pyrenoid matrix. We find that the mutant's phenotypes are due to disruption of a gene, which we call StArch Granules Abnormal 1 (SAGA1) because starch sheath granules, or plates, in mutants lacking SAGA1 are more elongated and thinner than those of wild type. SAGA1 contains a starch binding motif, suggesting that it may directly regulate starch sheath morphology. SAGA1 localizes to multiple puncta and streaks in the pyrenoid and physically interacts with the small and large subunits of the carbon-fixing enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), a major component of the liquid-like pyrenoid matrix. Our findings suggest a biophysical mechanism by which starch sheath morphology affects pyrenoid number and CO2-concentrating mechanism function, advancing our understanding of the structure and function of this biogeochemically important organelle. More broadly, we propose that the number of phase-separated organelles can be regulated by imposing constraints on their surface area.

Chloroplast Chaperonin: An Intricate Protein Folding Machine for Photosynthesis.

Group I chaperonins are large cylindrical-shaped nano-machines that function as a central hub in the protein quality control system in the bacterial cytosol, mitochondria and chloroplasts. In chloroplasts, proteins newly synthesized by chloroplast ribosomes, unfolded by diverse stresses, or translocated from the cytosol run the risk of aberrant folding and aggregation. The chloroplast chaperonin system assists these proteins in folding into their native states. A widely known protein folded by chloroplast chaperonin is the large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), an enzyme responsible for the fixation of inorganic CO2 into organic carbohydrates during photosynthesis. Chloroplast chaperonin was initially identified as a Rubisco-binding protein. All photosynthetic eucaryotes genomes encode multiple chaperonin genes which can be divided into α and β subtypes. Unlike the homo-oligomeric chaperonins from bacteria and mitochondria, chloroplast chaperonins are more complex and exists as intricate hetero-oligomers containing both subtypes. The Group I chaperonin requires proper interaction with a detachable lid-like co-chaperonin in the presence of ATP and Mg2+ for substrate encapsulation and conformational transition. Besides the typical Cpn10-like co-chaperonin, a unique co-chaperonin consisting of two tandem Cpn10-like domains joined head-to-tail exists in chloroplasts. Since chloroplasts were proposed as sensors to various environmental stresses, this diversified chloroplast chaperonin system has the potential to adapt to complex conditions by accommodating specific substrates or through regulation at both the transcriptional and post-translational levels. In this review, we discuss recent progress on the unique structure and function of the chloroplast chaperonin system based on model organisms Chlamydomonas reinhardtii and Arabidopsis thaliana. Knowledge of the chloroplast chaperonin system may ultimately lead to successful reconstitution of eukaryotic Rubisco in vitro.

A DIGE proteomic analysis of wheat flag leaf treated with TERRA-SORB® foliar, a free amino acid high content biostimulant

The flag leaf is the most important source of carbohydrate during wheat kernel filling. Around a 75% of all sugars stored in the kernel come from carbon fixed by this leaf. Terra-Sorb® foliar is an L-α-amino acid-based product from enzymatic hydrolysis for foliar application with a high ratio of free to total amino acids. Previous agronomical studies carried out on grassy, horticultural and tree crops have shown that the application of Terra-Sorb® increases photosynthetic plant activity and chlorophyll content, promotes rapid recovery from stress and improves fruit set. In this work, we have undertaken a proteomic approach to explore molecular mechanisms potentially involved in the stimulating effect of Terra-Sorb® Foliar on wheat yield when applied in commercial fields. Wheat plants at the flag leaf stage were treated, and a DIGE approach was used to compare the proteomes of treated vs. control plants in four biological replicates. Thirty-seven protein spots were found to change in abundance (ANOVA p The deregulated proteins identified were mainly related to the life cycle of Rubisco. Importantly, two proteins involved in the positive regulation of Rubisco activity, namely Rubisco activase, and the large subunit of Rubisco binding protein, were found up-regulated in treated plants, suggesting a better performance of Rubisco. Down-regulated proteins were of metabolic and anti-stress enzymes, including Cu/Zn superoxide dismutase that protects photosystem II from photooxidation. In conclusion, significant changes were shown to occur in the wheat flag leaf proteome upon Terra-Sorb® Foliar application. The deregulated proteins identified are directly or indirectly involved in the CO fixation which may correlate with the known stimulating effect of Terra-Sorb® Foliar of wheat yield, although further functional experiments are needed to validate the proposed hypothesis.

Protein changes and proteolytic degradation in red and white clover plants subjected to waterlogging

Red (Trifolium pratense L., cv. “Start”) and white clover varieties (Trifolium repens L., cv. “Debut” and cv. “Haifa”) were waterlogged for 14 days and subsequently recovered for the period of 21 days. Physiological and biochemical responses of the clover varieties were distinctive, which suggested different sensitivity toward flooding. The comparative study of morphological and biochemical parameters such as stem length, leaflet area, dry weight, protein content, protein pattern and proteolytic degradation revealed prominent changes under waterlogging conditions. Protease activity in the stressed plants increased significantly, especially in red clover cv. “Start”, which exhibited eightfold higher azocaseinolytic activity compared to the control. Changes in the protein profiles were detected by SDS-PAGE electrophoresis. The specific response of some proteins (Rubisco, Rubisco-binding protein, Rubisco activase, ClpA and ClpP protease subunits) toward the applied stress was assessed by immunoblotting. The results characterized the red clover cultivar “Start” as the most sensitive toward waterlogging, expressing reduced levels of Rubisco large and small subunits, high content of ClpP protease subunits and increased activity of protease isoforms.

Drought stress tolerance of red and white clover–comparative analysis of some chaperonins and dehydrins

The ecophysiological function linked to the contribution of the legume to the nitrogen supply of the sward, as well as its high content in pastures, make red ( Trifolim pratense) and white clover ( Trifolium repens) forage plants of economic importance in temperate regions. The study aimed to characterize the expression profiles of some important stress tolerance related proteins in red clover (cv. “Start”), and two white clover cultivars – cv. “Haifa” (medium-leafed) and cv. “Debut” (small-leafed). An attempt has been made to explain the differences in red and white clover potential to sustain unfavorable environmental conditions regarding the obtained results from protein and gene profiling. Rubisco binding protein (RBP), low molecular weight heat shock proteins (HSP), calpains (ClpA and ClpP) and dehydrins (DHN) responded significantly to drought. White clover cv. “Debut” developed the lowest leaf water deficit (WD) compared to the one detected in red clover and the medium leafed white clover cultivar “Haifa”. Immunoblot and RT-PCR showed that the small leafed white clover cv. “Debut” copes with drought stress most efficiently. Detailed gene expression analysis revealed that Y 2SK type dehydrins were subjected to alternative splicing under drought and the transcripts were strongly induced in the more drought tolerant small-leafed white clover cultivar “Debut”. A homolog sequence of Y 2K dehydrin in T. pratense (GenBank ID: JF748409) and T. repens (GenBank ID: JF748410) have been amplified and an increased transcipt levels of JF748409 were detected in T. pratense drought stressed leaves. The expression pattern of SK 2 transcripts showed that this dehydrin type has been down-regulated in both white clover cultivars under water deprivation.

Plant physiology and proteomics reveals the leaf response to drought in alfalfa (Medicago sativa L.)

Despite its relevance, protein regulation, metabolic adjustment, and the physiological status of plants under drought is not well understood in relation to the role of nitrogen fixation in nodules. In this study, nodulated alfalfa plants were exposed to drought conditions. The study determined the physiological, metabolic, and proteomic processes involved in photosynthetic inhibition in relation to the decrease in nitrogenase (Nase) activity. The deleterious effect of drought on alfalfa performance was targeted towards photosynthesis and Nase activity. At the leaf level, photosynthetic inhibition was mainly caused by the inhibition of Rubisco. The proteomic profile and physiological measurements revealed that the reduced carboxylation capacity of droughted plants was related to limitations in Rubisco protein content, activation state, and RuBP regeneration. Drought also decreased amino acid content such as asparagine, and glutamic acid, and Rubisco protein content indicating that N availability limitations were caused by Nase activity inhibition. In this context, drought induced the decrease in Rubisco binding protein content at the leaf level and proteases were up-regulated so as to degrade Rubisco protein. This degradation enabled the reallocation of the Rubisco-derived N to the synthesis of amino acids with osmoregulant capacity. Rubisco degradation under drought conditions was induced so as to remobilize Rubisco-derived N to compensate for the decrease in N associated with Nase inhibition. Metabolic analyses showed that droughted plants increased amino acid (proline, a major compound involved in osmotic regulation) and soluble sugar (D-pinitol) levels to contribute towards the decrease in osmotic potential (Ψs). At the nodule level, drought had an inhibitory effect on Nase activity. This decrease in Nase activity was not induced by substrate shortage, as reflected by an increase in total soluble sugars (TSS) in the nodules. Proline accumulation in the nodule could also be associated with an osmoregulatory response to drought and might function as a protective agent against ROS. In droughted nodules, the decrease in N2 fixation was caused by an increase in oxygen resistance that was induced in the nodule. This was a mechanism to avoid oxidative damage associated with reduced respiration activity and the consequent increase in oxygen content. This study highlighted that even though drought had a direct effect on leaves, the deleterious effects of drought on nodules also conditioned leaf responsiveness.

10.1007/s11183-008-2005-0

Two-dimensional electrophoresis was used to separate proteins from crude extracts of pea (Pisum sativum L.) leaves, and thus isolated proteins were subjected to Western blot analysis with monoclonal antibodies against PY20 phosphotyrosine polypeptides. This analysis revealed 44 polypeptides phosphorylated on tyrosine residues. Phosphorylation of some of these proteins was changed under the action of epibrassinolide. Some of these polypeptides were identified by means of MALDI-TOF MS analysis. The results indicate that eight of these proteins belong to the Calvin cycle enzymes, namely, the isoforms of Rubisco large and small subunits, fructose-1,6-phosphate aldolases 1 and 2, and the precursor of α-subunit of Rubisco-binding protein. The observed changes in phosphorylation of these proteins may partly explain the effects of brassinosteroids on photosynthesis. The tyrosine phosphorylation sites were identified in silico for the fragments of polypeptides examined.

Rubisco and some chaperone protein responses to water stress and rewatering at early seedling growth of drought sensitive and tolerant wheat varieties

Four wheat varieties differing in their drought tolerance were subjected to severe but recoverable water stress at seedling stage. Growth parameters, leaf water deficit (WD) and electrolyte leakage (EL) were used to evaluate the stress intensity and the extent of recovery. The physiological response of the varieties was quite similar under severe drought. Leaf protein patterns and levels of some individual proteins relevant to ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) maintenance were studied in control, stressed and recovering plants by electrophoresis and immunoblotting. The bands representing Rubisco large subunit (RLS), N- and C-terminus of RLS, Rubisco activase (RA) and Rubisco binding protein (RBP, cpn 60), as well as the chaperone and proteolytic subunits of the Clp protease complex were identified using polyclonal antibodies. Under drought conditions RLS, Clp proteases and especially RBP were enhanced, whereas the RA band was only slightly affected. The drought tolerant varieties had higher RBP content in the controls and drought treated plants. Its concentration could be a potential marker for drought tolerance.

Impact of an exceptionally hot dry summer on photosynthetic traits in oak (Quercus pubescens) leaves

Climatic constraints on diurnal variations in photosynthetic traits were investigated in oaks (Quercus pubescens Willd.) growing in the Swiss Alps. The measurement period included the summer of 2003, when central Europe experienced a record-breaking heat wave. During the summer, a combination of moderate heat and drought caused a reduction in photosynthetic CO(2) assimilation rate (P(n)) by mid-morning, which increased by the afternoon. More extreme drought and heat caused a sharp day-long reduction in P(n). These effects were closely related to changes in stomatal conductance (g(s)), but low g(s) was unaccompanied by low intercellular CO(2) concentrations (C(i)). Around midday, a combination of heat and drought increased C(i), indicating metabolic limitation of photosynthesis. Chlorophyll a (Chl a) fluorescence measurements revealed reversible down-regulation of photosystem (PS) II activity during the day, which was accentuated by heat and drought and correlated with diurnal variation in zeaxanthin accumulation. A combination of heat and drought reduced leaf Chl a + b concentrations and increased ratios of total carotenoids, xanthophyll-cycle carotenoids and lutein to Chl a + b. The combination of summertime heat and drought altered the 77 K Chl fluorescence emission spectra of leaves, indicating changes in the organization of thylakoid membranes, but it had no effect on the amounts of the major light-harvesting Chl-a/b-binding protein of PSII (LHCII), Rubisco, Rubisco activase, Rubisco-binding protein (cpn-60), phosphoribulokinase and chloroplast ATP synthase. The results demonstrate that Q. pubescens can maintain photosynthetic capacity under adverse summer conditions.

Effect of epibrassinolide on tyrosine phosphorylation of the calvin cycle enzymes

Two-dimensional electrophoresis was used to separate proteins from crude extracts of pea (Pisum sativum L.) leaves, and thus isolated proteins were subjected to Western blot analysis with monoclonal antibodies against PY20 phosphotyrosine polypeptides. This analysis revealed 44 polypeptides phosphorylated on tyrosine residues. Phosphorylation of some of these proteins was changed under the action of epibrassinolide. Some of these polypeptides were identified by means of MALDI-TOF MS analysis. The results indicate that eight of these proteins belong to the Calvin cycle enzymes, namely, the isoforms of Rubisco large and small subunits, fructose-1,6-phosphate aldolases 1 and 2, and the precursor of α-subunit of Rubisco-binding protein. The observed changes in phosphorylation of these proteins may partly explain the effects of brassinosteroids on photosynthesis. The tyrosine phosphorylation sites were identified in silico for the fragments of polypeptides examined.

Proteome Changes in Leaves from Grapevine (Vitis vinifera L.) Transformed for Alcohol Dehydrogenase Activity

A proteomic approach has been used to study changes in leaf protein content from plants transformed for alcohol dehydrogenase (ADH) activity. Individual quantitative analysis of 190-436 spots separated by two-dimensional electrophoresis was performed, and spots displaying significant quantitative changes between control (C), sense (S), and antisense (R) transformants were selected using Student's t test. Of the 14 spots selected and further analyzed after trypsic digestion, 9 could be identified by MS analysis and 5 by LC-MS/MS. Identified proteins had mainly a chloroplastic origin: four rubisco large subunits, one rubisco binding protein, two glutamine synthetases, one elongation factor Tu, one ATP synthase beta subunit, and one plastidic aldolase. Proteins with other localization were also identified, such as a UDP-glucose pyrophosphorylase, a mitochondrial aminomethyltransferase, a linalool synthase, which comigrated with the protein identified as elongation factor Tu, an enolase comigrating with a glyceraldehyde 3-phosphate dehydrogenase, and a mixture of eight proteins among which were a dehydroascorbate reductase, a chalcone isomerase, and a rubisco activase. The results emphasize the changes in carbon metabolism-associated proteins linked to the alteration in ADH activity of grapevine transformant leaves.

Heat stress effects on ribulose-1,5-bisphosphate carboxylase/oxygenase, Rubisco binding protein and Rubisco activase in wheat leaves

Changes in chlorophyll content, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) binding protein (RBP), Rubisco activase (RA), Rubisco large (LS) and small (SS) subunits, and electrolyte leakage were investigated in wheat leaf segments during heat stress (HS) for 1 h and for 24 h at 40 °C in darkness or in light, as well as after recovery from heat stress (HSR) for 24 h at 25 °C in light. The 24-h HS treatment in darkness decreased irreversibly photosynthetic pigments, soluble proteins, RBP, RA, Rubisco LS and SS. An increase in RA and RBP protein contents was observed under 24-h HS and HSR in light. This increase was in accordance with their role as chaperones and the function of RBP as a heat shock protein.

Biochemical changes in barley plants after excessive supply of copper and manganese

The present study was undertaken to identify changes in some important proteins involved in CO 2 fixation (Rubisco, Rubisco activase (RA), Rubisco binding protein (RBP)), NH 4 + assimilation (glutamine synthetase (GS) and glutamate synthase (GOGAT)), using immunoblotting, and in the antioxidative defense as a result of Cu or Mn excess in barley leaves ( Hordeum vulgare L. cv. Obzor). Activities and isoenzyme patterns of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and catalase (CAT), as well as the levels of ascorbate (ASC), non-protein sulfhydryl groups, hydrogen peroxide and oxidative damage to proteins were determined. Data were correlated to the accumulation of Cu or Mn in the leaves after 5 days supply of heavy metal (HM) excess in the nutrient solution. In the highest Cu excess (1500 μM), Rubisco LS and SS were reduced considerably whereas under the highest Mn concentrations (18,300 μM) only minor changes in Rubisco subunits were detected. The RBP was diminished under the highest concentrations of both Cu or Mn. The bands of RA changed differently comparing Cu and Mn toxicity. GS decreased and GOGAT was absent under the highest concentration of Cu. At Mn excess Fd-GOGAT diminished whereas GS was not apparently changed. The development of toxicity symptoms corresponded to an accumulation of Cu or Mn in the leaves and to a gradual increase in protein carbonylation, a lower SOD activity and elevated CAT and GPX activities. APX activity was diminished under Mn toxicity and was not changed under Cu excess. Generally, changes in the isoenzyme profiles were similar under both toxicities. An accumulation of H 2O 2 was observed only at Mn excess. Contrasting changes in the low-molecular antioxidants were detected when comparing both toxicities. Cu excess affected mainly the non-protein SH groups, while Mn influenced the ASC content. Oxidative stress under Cu or Mn toxicity was most probably the consequence of depletion in low-molecular antioxidants as a result of their involvement in detoxification processes and disbalance in antioxidative enzymes. The link between heavy metal accumulation in leaves, leading to different display of oxidative stress, and changes in individual chloroplast proteins is discussed in the article.

Heat sensitivity of Rubisco, Rubisco activase and Rubisco binding protein in higher plants

During the past few years the investigations concerning Rubisco and the changes of its activity and properties at elevated temperature were reconsidered with special reference to the important role of Rubisco activase and Rubisco binding protein. The major changes in Rubisco, Rubisco activase and Rubisco binding protein reported recently are presented in this review. New information on these proteins, including their changes under heat stress conditions, is discussed together with open questions.

A molecular chaperone from a thermophilic archaebacterium is related to the eukaryotic protein t-complex polypeptide-1

There is evidence to suggest that components of archaebacteria are evolutionarily related to cognates in the eukaryotic cytosol. We postulated that the major heat-shock protein of the thermophilic archaebacterium, Sulfolobus shibatae, is a molecular chaperone and that it is related to an as-yet unidentified chaperone component in the eukaryotic cytosol. Acquired thermotolerance in S. shibatae correlates with the predominant synthesis of this already abundant protein, referred to as thermophilic factor 55 (TF55). TF55 is a homo-oligomeric complex of two stacked 9-membered rings, closely resembling the 7-membered-ring complexes of the chaperonins, groEL, hsp60 and Rubisco-binding protein. The TF55 complex binds unfolded polypeptides in vitro and has ATPase activity-features consistent with its being a molecular chaperone. The primary structure of TF55, however, is not significantly related to the chaperonins. On the other hand, it is highly homologous (36-40% identity) to a ubiquitous eukaryotic protein, t-complex polypeptide-1 (TCP1). In Saccharomyces cerevisiae, TCP1 is an essential protein that may play a part in mitotic spindle formation. We suggest that TF55 in archaebacteria and TCP1 in the eukaryotic cytosol are members of a new class of molecular chaperones.

Chromosomal location of genes for Rubisco small subunit and Rubisco-binding protein in common wheat

The genes coding for the Rubisco small subunit (SSU) and for the α-subunit of the Rubisco-binding protein were located to chromosome arms of common wheat. HindIII-digested total DNA from the hexaploid cultivar Chinese Spring and from ditelosomic and nullisomic-tetrasomic lines was probed with these two genes, whose chromosomal location was deduced from the disappearance of or from changes in the relative intensity of the relevant band(s). The Rubisco SSU pattern consisted of 14 bands, containing at least 21 different types of DNA fragments, which were allocated to two homoeologous groups: 15 to the short arm of group 2 chromosomes (4 to 2AS, 7 to 2BS, and 4 to 2DS) and 6 to the long arm of group 5 chromosomes (2 on each of arms 5AL, 5BL, and 5DL). The pattern of the Rubisco-binding protein consisted of three bands, each containing one type of fragment. These fragments were located to be on the short arm of group 2 chromosomes. The restriction fragment length polymorphism (RFLP) patterns of several hexaploid and tetraploid lines were highly conserved, whereas the patterns of several of their diploid progenitors were more variable. The variations found in the polyploid species were mainly confined to the B genome. The patterns of the diploids T. monococcum var. urartu and Ae. squarrosa were similar to those of the A and D genome, respectively, in polyploid wheats. The pattern of T. monococcum var. boeoticum was different from the patterns of the A genome, and the patterns of the diploids Ae. speltoides, Ae. longissima, and Ae. Searsii differed from that of the B genome.

Identification and metabolic characterization of the Zea mays mitochondrial homolog of the Escherichia coli groEL protein

We have characterized an abundant mitochondrial protein from Zea mays and have shown it to be structurally and metabolically indistinguishable from a previously described Tetrahymena thermophila and Saccharomyces cerevisiae mitochondrial protein, referred to as hsp60, which is homologous to the groEL protein of Escherichia coli. This Z. mays protein, which we also refer to as hsp60, was found to be antigenically quite distinct from the chloroplast Rubisco-binding protein, another groEL homolog. Using an antiserum directed against the T. thermophila hsp60, we determined that the relative concentration of Z. mays hsp60 was two to four times higher in mitochondria isolated from tissues of early developmental stages than that found in mitochondria isolated from more adult tissues. Given the known and suggested roles of the other members of the groEL family of proteins, our results suggest that the Z. mays hsp60 may play an important role in mitochondrial biogenesis during early plant development.

Characterization of the yeast HSP60 gene coding for a mitochondrial assembly factor

The hsp60 protein isolated from the protozoan Tetrahymena thermophila is induced in response to heat stress and is a member of an immunologically conserved family represented in Escherichia coli and in mitochondria of plants and animals. We report here the cloning and characterization of a nuclear gene, HSP60, which codes for the hsp60 homologue from the yeast Saccharomyces cerevisiae. Nucleotide sequence analysis revealed that yeast hsp60 is related to the groEL protein of E. coli and the RUBISCO-binding protein (RBP) of chloroplasts. HSP60 was found to be the genetic locus of the conditional-lethal mutation described by Cheng et al., which at non-permissive temperature is defective in the assembly of several different multisubunit complexes in mitochondria. These data are consistent with the hypothesis that the groEL-related proteins serve an evolutionarily conserved function as accessory factors facilitating the folding and/or association of individual subunits of multimeric protein complexes.

Identification and metabolic characterization of the Zea mays mitochondrial homolog of the Escherichia coli groEL protein

We have characterized an abundant mitochondrial protein from Zea mays and have shown it to be structurally and metabolically indistinguishable from a previously described Tetrahymena thermophila and Saccharomyces cerevisiae mitochondrial protein, referred to as hsp60, which is homologous to the groEL protein of Escherichia coli. This Z. mays protein, which we also refer to as hsp60, was found to be antigenically quite distinct from the chloroplast Rubisco-binding protein, another groEL homolog. Using an antiserum directed against the T. thermophila hsp60, we determined that the relative concentration of Z. mays hsp60 was two to four times higher in mitochondria isolated from tissues of early developmental stages than that found in mitochondria isolated from more adult tissues. Given the known and suggested roles of the other members of the groEL family of proteins, our results suggest that the Z. mays hsp60 may play an important role in mitochondrial biogenesis during early plant development.