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RACK1 genes regulate plant development with unequal genetic redundancy in Arabidopsis.

Guo J, Chen JG - BMC Plant Biol. (2008)

Bottom Line: We found that unlike in RACK1A, loss-of-function mutations in RACK1B or RACK1C do not confer apparent defects in plant development, including rosette leaf production and root development.These results suggested that RACK1 genes are critical regulators of plant development and that RACK1 genes function in an unequally redundant manner.Both the difference in RACK1 gene expression level and the cross-regulation are likely the molecular determinants of their unequal genetic redundancy.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Botany, University of British Columbia, Vancouver, BC, Canada. jimguo@interchange.ubc.ca

ABSTRACT

Background: RACK1 is a versatile scaffold protein in mammals, regulating diverse developmental processes. Unlike in non-plant organisms where RACK1 is encoded by a single gene, Arabidopsis genome contains three RACK1 homologous genes, designated as RACK1A, RACK1B and RACK1C, respectively. Previous studies indicated that the loss-of-function alleles of RACK1A displayed multiple defects in plant development. However, the functions of RACK1B and RACK1C remain elusive. Further, the relationships between three RACK1 homologous genes are unknown.

Results: We isolated mutant alleles with loss-of-function mutations in RACK1B and RACK1C, and examined the impact of these mutations on plant development. We found that unlike in RACK1A, loss-of-function mutations in RACK1B or RACK1C do not confer apparent defects in plant development, including rosette leaf production and root development. Analyses of rack1a, rack1b and rack1c double and triple mutants, however, revealed that rack1b and rack1c can enhance the rack1a mutant's developmental defects, and an extreme developmental defect and lethality were observed in rack1a rack1b rack1c triple mutant. Complementation studies indicated that RACK1B and RACK1C are in principle functionally equivalent to RACK1A. Gene expression studies indicated that three RACK1 genes display similar expression patterns but are expressed at different levels. Further, RACK1 genes positively regulate each other's expression.

Conclusion: These results suggested that RACK1 genes are critical regulators of plant development and that RACK1 genes function in an unequally redundant manner. Both the difference in RACK1 gene expression level and the cross-regulation are likely the molecular determinants of their unequal genetic redundancy.

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Related in: MedlinePlus

Multiple amino acid sequence alignment of RACK1 in plants and in humans. The amino acid sequences were aligned by CLUSTALW multiple alignment of BioEdit Sequence Alignment Editor . Amino acids that are identical or similar are shaded with black or gray, respectively. Gaps are shown as dashed lines. The proteins aligned are (name of species and accession number in parentheses): RACK1A_At (Arabidopsis thaliana, NP_173248), RACK1B_At (Arabidopsis thaliana, NP_175296), RACK1C_At (Arabidopsis thaliana, NP_188441), RACK1A_Os (Oryza sativa, NP_001043910), RACK1B_Os (Oryza sativa, NP_001056254), RACK1_Pt (Populus trichocarpa, ABK92879), RACK1 _Vv (Vitis vinifera, CAN61810), and RACK1_Hs (Homo sapiens, NP_006089). The positions of GH and WD dipeptides in each WD40 repeat are indicated by triangles and asterisks, respectively, on the top of residues. The positions for WD repeat domains were obtained from the SMART database .
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Figure 1: Multiple amino acid sequence alignment of RACK1 in plants and in humans. The amino acid sequences were aligned by CLUSTALW multiple alignment of BioEdit Sequence Alignment Editor . Amino acids that are identical or similar are shaded with black or gray, respectively. Gaps are shown as dashed lines. The proteins aligned are (name of species and accession number in parentheses): RACK1A_At (Arabidopsis thaliana, NP_173248), RACK1B_At (Arabidopsis thaliana, NP_175296), RACK1C_At (Arabidopsis thaliana, NP_188441), RACK1A_Os (Oryza sativa, NP_001043910), RACK1B_Os (Oryza sativa, NP_001056254), RACK1_Pt (Populus trichocarpa, ABK92879), RACK1 _Vv (Vitis vinifera, CAN61810), and RACK1_Hs (Homo sapiens, NP_006089). The positions of GH and WD dipeptides in each WD40 repeat are indicated by triangles and asterisks, respectively, on the top of residues. The positions for WD repeat domains were obtained from the SMART database .

Mentions: Structurally, RACK1 proteins in plants are similar to those in mammals, containing a seven-bladed β-propeller [14]. However, analysis of RACK1 proteins in plants and in non-plant organisms revealed an important feature of plant RACK1 proteins: some plants have more than one RACK1 genes, in contrast to the single copy of RACK1 gene in non-plant organisms. For example, the sequenced genomes of rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana) contain two and three RACK1 homologous genes, respectively (Figure 1). The three RACK1 proteins encoded by the Arabidopsis genome were designated as RACK1A, RACK1B and RACK1C, respectively [15]. Previously, we provided evidence that RACK1A mediates multiple hormone responses and developmental processes [15]. However, the functions of the other two Arabidopsis RACK1 genes, RACK1B and RACK1C, and the relationship between Arabidopsis RACK1 genes remain unknown. Here we demonstrate that although RACK1B and RACK1C genes are likely dispensable, they still contribute significantly to the RACK1A-regulated developmental processes in Arabidopsis. We provide evidence that the difference in the gene expression level and the cross-regulation are likely the molecular determinants of unequal genetic redundancy of RACK1 genes in regulating plant development.


RACK1 genes regulate plant development with unequal genetic redundancy in Arabidopsis.

Guo J, Chen JG - BMC Plant Biol. (2008)

Multiple amino acid sequence alignment of RACK1 in plants and in humans. The amino acid sequences were aligned by CLUSTALW multiple alignment of BioEdit Sequence Alignment Editor . Amino acids that are identical or similar are shaded with black or gray, respectively. Gaps are shown as dashed lines. The proteins aligned are (name of species and accession number in parentheses): RACK1A_At (Arabidopsis thaliana, NP_173248), RACK1B_At (Arabidopsis thaliana, NP_175296), RACK1C_At (Arabidopsis thaliana, NP_188441), RACK1A_Os (Oryza sativa, NP_001043910), RACK1B_Os (Oryza sativa, NP_001056254), RACK1_Pt (Populus trichocarpa, ABK92879), RACK1 _Vv (Vitis vinifera, CAN61810), and RACK1_Hs (Homo sapiens, NP_006089). The positions of GH and WD dipeptides in each WD40 repeat are indicated by triangles and asterisks, respectively, on the top of residues. The positions for WD repeat domains were obtained from the SMART database .
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2577656&req=5

Figure 1: Multiple amino acid sequence alignment of RACK1 in plants and in humans. The amino acid sequences were aligned by CLUSTALW multiple alignment of BioEdit Sequence Alignment Editor . Amino acids that are identical or similar are shaded with black or gray, respectively. Gaps are shown as dashed lines. The proteins aligned are (name of species and accession number in parentheses): RACK1A_At (Arabidopsis thaliana, NP_173248), RACK1B_At (Arabidopsis thaliana, NP_175296), RACK1C_At (Arabidopsis thaliana, NP_188441), RACK1A_Os (Oryza sativa, NP_001043910), RACK1B_Os (Oryza sativa, NP_001056254), RACK1_Pt (Populus trichocarpa, ABK92879), RACK1 _Vv (Vitis vinifera, CAN61810), and RACK1_Hs (Homo sapiens, NP_006089). The positions of GH and WD dipeptides in each WD40 repeat are indicated by triangles and asterisks, respectively, on the top of residues. The positions for WD repeat domains were obtained from the SMART database .
Mentions: Structurally, RACK1 proteins in plants are similar to those in mammals, containing a seven-bladed β-propeller [14]. However, analysis of RACK1 proteins in plants and in non-plant organisms revealed an important feature of plant RACK1 proteins: some plants have more than one RACK1 genes, in contrast to the single copy of RACK1 gene in non-plant organisms. For example, the sequenced genomes of rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana) contain two and three RACK1 homologous genes, respectively (Figure 1). The three RACK1 proteins encoded by the Arabidopsis genome were designated as RACK1A, RACK1B and RACK1C, respectively [15]. Previously, we provided evidence that RACK1A mediates multiple hormone responses and developmental processes [15]. However, the functions of the other two Arabidopsis RACK1 genes, RACK1B and RACK1C, and the relationship between Arabidopsis RACK1 genes remain unknown. Here we demonstrate that although RACK1B and RACK1C genes are likely dispensable, they still contribute significantly to the RACK1A-regulated developmental processes in Arabidopsis. We provide evidence that the difference in the gene expression level and the cross-regulation are likely the molecular determinants of unequal genetic redundancy of RACK1 genes in regulating plant development.

Bottom Line: We found that unlike in RACK1A, loss-of-function mutations in RACK1B or RACK1C do not confer apparent defects in plant development, including rosette leaf production and root development.These results suggested that RACK1 genes are critical regulators of plant development and that RACK1 genes function in an unequally redundant manner.Both the difference in RACK1 gene expression level and the cross-regulation are likely the molecular determinants of their unequal genetic redundancy.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Botany, University of British Columbia, Vancouver, BC, Canada. jimguo@interchange.ubc.ca

ABSTRACT

Background: RACK1 is a versatile scaffold protein in mammals, regulating diverse developmental processes. Unlike in non-plant organisms where RACK1 is encoded by a single gene, Arabidopsis genome contains three RACK1 homologous genes, designated as RACK1A, RACK1B and RACK1C, respectively. Previous studies indicated that the loss-of-function alleles of RACK1A displayed multiple defects in plant development. However, the functions of RACK1B and RACK1C remain elusive. Further, the relationships between three RACK1 homologous genes are unknown.

Results: We isolated mutant alleles with loss-of-function mutations in RACK1B and RACK1C, and examined the impact of these mutations on plant development. We found that unlike in RACK1A, loss-of-function mutations in RACK1B or RACK1C do not confer apparent defects in plant development, including rosette leaf production and root development. Analyses of rack1a, rack1b and rack1c double and triple mutants, however, revealed that rack1b and rack1c can enhance the rack1a mutant's developmental defects, and an extreme developmental defect and lethality were observed in rack1a rack1b rack1c triple mutant. Complementation studies indicated that RACK1B and RACK1C are in principle functionally equivalent to RACK1A. Gene expression studies indicated that three RACK1 genes display similar expression patterns but are expressed at different levels. Further, RACK1 genes positively regulate each other's expression.

Conclusion: These results suggested that RACK1 genes are critical regulators of plant development and that RACK1 genes function in an unequally redundant manner. Both the difference in RACK1 gene expression level and the cross-regulation are likely the molecular determinants of their unequal genetic redundancy.

Show MeSH
Related in: MedlinePlus