Os05g0519700

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==Annotated Information==ClpB-cytoplasmic (ClpB-cyt)/Hsp100 is an important chaperone protein in rice. Cellular expression of OsClpB-cyt transcript is governed by heat stress, metal stress, and developmental cues.

Function

ClpB-cyt/HSP100 protein acts as chaperone, mediating disaggregation of denatured proteins. Previous studies have shown that ClpB-cyt/HSP100 gene belongs to the group class I Clp ATPase proteins and ClpB-cyt/HSP100 transcript is regulated by heat stress and developmental cues.

Heat stress threatens future prospects of increased grain production in crops. Rice (Oryza sativa) is most important world food crop. The production of rice is getting severely affected with increases in mean global temperature. According to estimates, yield of rice declines by 10% for every 1°C increase in growing period minimum temperature in the dry season . Processes like spikelet fertility, grain quality and yield processes in rice are considered to be especially sensitive to heat stress . For breeding heat tolerant rice, it is important that molecular components that underlie the heat shock response in this species are understood . Microarray profiling data have shown that heat stress response in maturing tomato microspores involves heat shock proteins, ROS scavengers, hormones and sugars . Understandably, the major molecular changes in rice plants as affected by heat stress need to be worked out. This is especially relevant since rice has emerged as a model plant species of the group monocots due to its small genome size, availability of large collection of full-length cDNAs (FLcDNAs) and for the fact that the whole genome of this plant species is completely sequenced. This crop has attracted a great deal of efforts for the elucidation of gene functions; completion of genome sequencing in rice has paved way for comprehensive functional characterization of genes, transcription factors, signaling components and promoters . The completed rice genome sequence has been used for the characterization of a large number of gene families involved in diverse processes and pathways. However, with almost 42000 genes, several of them unknown, there are ample proteins still left to be characterized in this important crop species. In recent years, comprehensive details on heat shock regulated rice HSP20, HSP70, HSP90 and HSF gene families have been reported .

Expression

HSP100 is a major heat-regulated protein family in diverse organisms. Across the living systems, common features of HSP100 chaperone action include transient interactions with non-native protein species, in the prevention of aggregation and promotion of correct folding and assembly, or in unfolding for translocation or targeting to proteases. Singla and Grover showed that homologues of yeast HSP104protein are expressed in heat shocked rice seedlings. It was subsequently established that apart from heat, rice HSP100 expression is developmentally-controlled as seeds and developing embryos of rice show high constitutive levels of this protein.

Expression characteristics of plant Hsp100 members.Hsp100 transcript/protein expression is induced during heat stress in Arabidopsis, soybean, rice, maize, tobacco and wheat. There are also indications that Hsp100 transcript/protein is induced by desiccation, low temperature and ABA. Apart from stress-regulation, Hsp100 transcript and protein are developmentally regulated in plants. In non-stressed maize, Hsp100 is expressed to a high level in the tassel at the pre-meiosis stage, the ear (including silks) and the developing endosperm and embryo.

Detailed analysis of the amino acid sequence has revealed that Hsp100 members contain several conserved signatures. Schirmer divided Hsp100 into class I (Hsp100 types A–D; containing two nucleotide-binding domains) and class II (Hsp100 types M, N, X, and Y; containing one nucleotide-binding domain) proteins. The molecular weights of the Hsp100 proteins is considered to vary between 75 and 100 kDa because of the size of the non-conserved spacers between the 2 domains and additional sequences at the Cand N-termini. Basically, Hsp100 proteins are composed of five specific domains as follows: (i) amino (N) - terminal domain, (ii) nucleotide – binding domain 1 (NBD1), (iii) middle domain, (iv) NBD2 and (v) carboxyl (C) - terminal domain. The conserved sequences of the five domains include (i) signature sequence I in the N-terminal domain, (ii) Walker A, Walker B1, and Walker B2 sequences in the NBD1, (iii) signature sequence II and signature sequence III in the middle domain, (iv) Walker A and Walker B sequences in NBD2 and (v) signature sequence IV and V in the C-terminal domain. Based on more extensive analysis with larger spectrum of plant species, Agarwal reported further specific alterations in the amino acid sequence of various motifs of plant Hsp100 members.

Evolution

HSP100 proteins belong to ClpB family. Clp ATPases maintain quality of cellular proteins by performing the function of molecular chaperones and energy dependent proteases. Clp (Caseinolytic Protease) system was first identified as a heat shock inducible, multicomponent, ATP-dependent protease complex able to hydrolyze casein. Subsequent studies showed that the Clp system can hydrolyze numerous other proteins and peptides in both aggregated and non-aggregated forms Clp ATPases fall within the AAA+ superfamily of ATPases associated with a substantially broader range of biological processes. Class I ATPases (ClpA, ClpB, ClpC, ClpD) have two ATP binding domains and class II Clp ATPases (ClpM, ClpN, ClpX, ClpY) have one ATP binding domain. Clp proteins are localized in various cellular organelles in plants. Basically, Clp system members include three non-homologous gene families: ClpABCXY, ClpP and ClpQ. ClpACX members (but not ClpB) facilitate the activity of ClpP and some, such as ClpA and ClpX,can function as independent chaperones in roles analogous to those of DnaK and DnaJ proteins. In contrast, ClpP proteolytic subunit exhibits low levels of peptidolytic activity. Further, when ClpP is complexed with ClpA, ClpC or ClpX, active holoenzymes which are able to cleave denatured proteins are formed. ClpAP, ClpXP and HslUV proteases are similar in design to the eukaryotic 26 S proteasome, with the ATPase subunits guarding the entrance to the proteolytic chamber. Clp proteases in bacterial and eukaryotic systems have been implicated in vital cellular processes such as sporulation, DNA replication, protein turnover, stress tolerance and acclimation and regulation of gene expression. ClpB is different from ClpA, ClpX and HslU as it does not associate with peptidase subunits. The function of ClpB is also distinct from that of other Clp ATPases: this protein is not involved in protein degradation, instead it disaggregates and reactivates strongly aggregated proteins. The aggregation reversing activity of ClpB requires cooperation with the HSP70/HSP110 chaperone machinery.

Labs working on this gene

• Department of Plant Molecular Biology,University of Delhi South Campus,New Delhi 110021, India

References

[1] Peng S, Huang J, Sheehy JE, Laza RC, Visperas RM, Zhong X, Centeno GS, Khush GS, Cassman KG: Rice yields decline with higher night temperature from global warming. Proc Natl Acad Sci 2004, 101(27):9971-9975.

[2] Grover A, Chandramouli A, Agarwal S, Katiyar-Agarwal S, Agarwal M, Sahi C: Transgenic rice for tolerance against abiotic stresses. Rice Improvement in the Genomic Era Hawarth Press USADutta SK 2009, 237-267.

[3] Singh A, Grover A: Genetic engineering for heat tolerance in plants. Physiol Mol Biol Plants 2008, 14:155-166.

[4] Frank G, Pressman E, Ophir R, Althan L, Shaked R, Freedman M, Shen S, Firon N: Transcriptional profiling of maturing tomato (Solanum lycopersicum L.) microspores reveals the involvement of heat shock proteins, ROS scavengers, hormones, and sugars in the heat stress response. Journal of Experimental Botany 2009, 60(13):3891-3908.

[5] IRGSP: The map-based sequence of the rice genome. Nature 2005, 436(7052):793-800.

[6] Singla SL, Grover A: Antibodies raised against yeast HSP 104 cross-react with a heat- and abscisic acid-regulated polypeptide in rice. Plant Molecular Biology 1993, 22(6):1177-1180.

[7] Pareek A, Singla SL, Grover A: Immunological evidence for accumulation of two high-molecular-weight (104 and 90 kDa) HSPs in response to different stresses in rice and in response to high temperature stress in diverse plant genera. Plant Molecular Biology 1995, 29(2):293-301.

[8] Young T E, Ling J, Geisler-Lee C J, Tanguay R L, Caldwell C and Gallie D R 2001b Developmental and thermal regulation of the maize heat shock protein, HSP101; Plant Physiol. 127 777–791

[9] Agarwal M, Katiyar-Agarwal S and Grover A 2002 Plant Hsp100 protein: structure, function and regulation; Plant Sci. 163 397–405

[10] Gaurav Batra, Vineeta Singh Chauhan: Complexity of rice Hsp100 gene family: lessons from rice genome sequence data; J. Biosci.32 611–619.

Structured Information

Detailed analysis of the amino acid sequence has revealed that Hsp100 members contain several conserved signatures. Schirmer et al divided Hsp100 into class I (Hsp100 types A–D; containing two nucleotide-binding domains) and class II (Hsp100 types M, N, X, and Y; containing one nucleotide-binding domain) proteins. The molecular weights of the Hsp100 proteins is considered to vary between 75 and 100 kDa because of the size of the non-conserved spacers between the 2 domains and additional sequences at the Cand N-termini. Basically, Hsp100 proteins are composed of fi ve specifi c domains as follows: (i) amino (N) - terminal domain, (ii) nucleotide – binding domain 1 (NBD1), (iii) middle domain, (iv) NBD2 and (v) carboxyl (C) - terminal domain. The conserved sequences of the fi ve domains include (i) signature sequence I in the N-terminal domain, (ii) Walker A, Walker B1, and Walker B2 sequences in the NBD1, (iii) signature sequence II and signature sequence III in the middle domain, (iv) Walker A and Walker B sequences in NBD2 and (v) signature sequence IV and V in the C-terminal domain. Based on more extensive analysis with larger spectrum of plant species, Agarwal et al reported further specifi c alterations in the amino acid sequence of various motifs of plant Hsp100

members.