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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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rack1b-2 and rack1c-1 mutations enhance the rosette leaf phenotype of rack1a mutants. (A) The phenotype of rack1 mutants. Shown are plants grown for 48 days under 10/14 h photoperiod. Scale bars, 2 cm. (B) The number of rosette leaves of rack1 mutants. (C) The rate of rosette leaf production of rack1 mutants. The rate of rosette leaf production is expressed as the number of rosette leaves divided by the age of plants. (D) The size of rosette of rack1 mutants. The number of rosette leaves, the rate of rosette leaf production and the size of rosette were measured from plants grown for 48 d under 10/14 h photoperiod. Shown in (B) to (D) are the averages of at least four plants ± S.E. The same experiment was repeated twice with similar trends and the data from one experiment were presented. *, significant difference from Col, P < 0.05. #, significant difference from rack1a single mutant, P < 0,05. **, significant difference from rack1a-1 rack1b-2 double mutant, P < 0.05.
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Figure 3: rack1b-2 and rack1c-1 mutations enhance the rosette leaf phenotype of rack1a mutants. (A) The phenotype of rack1 mutants. Shown are plants grown for 48 days under 10/14 h photoperiod. Scale bars, 2 cm. (B) The number of rosette leaves of rack1 mutants. (C) The rate of rosette leaf production of rack1 mutants. The rate of rosette leaf production is expressed as the number of rosette leaves divided by the age of plants. (D) The size of rosette of rack1 mutants. The number of rosette leaves, the rate of rosette leaf production and the size of rosette were measured from plants grown for 48 d under 10/14 h photoperiod. Shown in (B) to (D) are the averages of at least four plants ± S.E. The same experiment was repeated twice with similar trends and the data from one experiment were presented. *, significant difference from Col, P < 0.05. #, significant difference from rack1a single mutant, P < 0,05. **, significant difference from rack1a-1 rack1b-2 double mutant, P < 0.05.

Mentions: Previously, we showed that loss-of-function mutations in one member of Arabidopsis RACK1 gene family, RACK1A, resulted in multiple defects in plant development [15]. Because loss-of-function alleles of RACK1B and RACK1C did not display apparent defects in plant development, we wanted to test if mutations in RACK1B or RACK1C can enhance the developmental defects of rack1a mutants. Therefore, we generated rack1a-1 rack1b-2 and rack1a-1 rack1c-1 double mutants. One of the most dramatic phenotypes observed in rack1a single mutants was the reduced number of rosette leaves [15]. Therefore, we grew single and double mutants together with wild-type (Col) under identical, short-day conditions with 10/14 h photoperiod, counted the number of rosette leaves in double mutants, and compared it with Col and rack1a-1 single mutant. We found that while rack1b-2 and rack1c-1 single mutants produced wild-type number of rosette leaves, both rack1b-2 and rack1c-1 significantly enhanced the phenotype of reduced number of rosette leaves of rack1a-1 single mutants (Figure 3A, B). When plants were grown under 10/14 h photoperiod for 48 days, wild-type produced approximately 30 rosette leaves, whereas rack1a-1 single mutant produced 22 rosette leaves. Under these conditions, rack1a-1 rack1b-2 and rack1a-1 rack1c-1 double mutants only produced about 16 and 19 rosette leaves, respectively (Figure 3B). The rate of rosette leaf production was reduced approximately 27% and 14%, respectively, in rack1a-1 rack1b-2 and rack1a-1 rack1c-1 double mutants, compared with rack1a-1 single mutant (Figure 3C). We also examined the rosette size by measuring the diameter of rosette of each genotype. Similar to the situation of number of rosette leaves, the diameter of rosette was significantly reduced in rack1a-1 single mutant, compared with wild-type plants, and such reduction was further enhanced in rack1a-1 rack1b-2 and rack1a-1 rack1c-1 double mutants (Figure 3D). Interestingly, no synergistic effect was observed between rack1b-2 and rack1c-1 mutations. Statistically, rack1b-2 rack1c-1 double mutants phenocopied parental single mutants and displayed wild-type traits of these phenotypes (Figure 3A, B).


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

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

rack1b-2 and rack1c-1 mutations enhance the rosette leaf phenotype of rack1a mutants. (A) The phenotype of rack1 mutants. Shown are plants grown for 48 days under 10/14 h photoperiod. Scale bars, 2 cm. (B) The number of rosette leaves of rack1 mutants. (C) The rate of rosette leaf production of rack1 mutants. The rate of rosette leaf production is expressed as the number of rosette leaves divided by the age of plants. (D) The size of rosette of rack1 mutants. The number of rosette leaves, the rate of rosette leaf production and the size of rosette were measured from plants grown for 48 d under 10/14 h photoperiod. Shown in (B) to (D) are the averages of at least four plants ± S.E. The same experiment was repeated twice with similar trends and the data from one experiment were presented. *, significant difference from Col, P < 0.05. #, significant difference from rack1a single mutant, P < 0,05. **, significant difference from rack1a-1 rack1b-2 double mutant, P < 0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 3: rack1b-2 and rack1c-1 mutations enhance the rosette leaf phenotype of rack1a mutants. (A) The phenotype of rack1 mutants. Shown are plants grown for 48 days under 10/14 h photoperiod. Scale bars, 2 cm. (B) The number of rosette leaves of rack1 mutants. (C) The rate of rosette leaf production of rack1 mutants. The rate of rosette leaf production is expressed as the number of rosette leaves divided by the age of plants. (D) The size of rosette of rack1 mutants. The number of rosette leaves, the rate of rosette leaf production and the size of rosette were measured from plants grown for 48 d under 10/14 h photoperiod. Shown in (B) to (D) are the averages of at least four plants ± S.E. The same experiment was repeated twice with similar trends and the data from one experiment were presented. *, significant difference from Col, P < 0.05. #, significant difference from rack1a single mutant, P < 0,05. **, significant difference from rack1a-1 rack1b-2 double mutant, P < 0.05.
Mentions: Previously, we showed that loss-of-function mutations in one member of Arabidopsis RACK1 gene family, RACK1A, resulted in multiple defects in plant development [15]. Because loss-of-function alleles of RACK1B and RACK1C did not display apparent defects in plant development, we wanted to test if mutations in RACK1B or RACK1C can enhance the developmental defects of rack1a mutants. Therefore, we generated rack1a-1 rack1b-2 and rack1a-1 rack1c-1 double mutants. One of the most dramatic phenotypes observed in rack1a single mutants was the reduced number of rosette leaves [15]. Therefore, we grew single and double mutants together with wild-type (Col) under identical, short-day conditions with 10/14 h photoperiod, counted the number of rosette leaves in double mutants, and compared it with Col and rack1a-1 single mutant. We found that while rack1b-2 and rack1c-1 single mutants produced wild-type number of rosette leaves, both rack1b-2 and rack1c-1 significantly enhanced the phenotype of reduced number of rosette leaves of rack1a-1 single mutants (Figure 3A, B). When plants were grown under 10/14 h photoperiod for 48 days, wild-type produced approximately 30 rosette leaves, whereas rack1a-1 single mutant produced 22 rosette leaves. Under these conditions, rack1a-1 rack1b-2 and rack1a-1 rack1c-1 double mutants only produced about 16 and 19 rosette leaves, respectively (Figure 3B). The rate of rosette leaf production was reduced approximately 27% and 14%, respectively, in rack1a-1 rack1b-2 and rack1a-1 rack1c-1 double mutants, compared with rack1a-1 single mutant (Figure 3C). We also examined the rosette size by measuring the diameter of rosette of each genotype. Similar to the situation of number of rosette leaves, the diameter of rosette was significantly reduced in rack1a-1 single mutant, compared with wild-type plants, and such reduction was further enhanced in rack1a-1 rack1b-2 and rack1a-1 rack1c-1 double mutants (Figure 3D). Interestingly, no synergistic effect was observed between rack1b-2 and rack1c-1 mutations. Statistically, rack1b-2 rack1c-1 double mutants phenocopied parental single mutants and displayed wild-type traits of these phenotypes (Figure 3A, B).

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