Limits...
RACK1 is a negative regulator of ABA responses in Arabidopsis.

Guo J, Wang J, Xi L, Huang WD, Liang J, Chen JG - J. Exp. Bot. (2009)

Bottom Line: It was found that the ABA-responsive marker genes, RD29B and RAB18, were up-regulated in rack1a mutants.Consistent with the view that RACK1 negatively regulates ABA responses, rack1a mutants lose water significantly more slowly from the rosettes and are hypersensitive to high concentrations of NaCl during seed germination.Taken together, these findings provide compelling evidence that RACK1 is a critical, negative regulator of ABA responses.

View Article: PubMed Central - PubMed

Affiliation: Department of Botany, University of British Columbia, Vancouver, BC, Canada.

ABSTRACT
Receptor for Activated C Kinase 1 (RACK1) is viewed as a versatile scaffold protein in mammals. The protein sequence of RACK1 is highly conserved in eukaryotes. However, the function of RACK1 in plants remains poorly understood. Accumulating evidence suggested that RACK1 may be involved in hormone responses, but the precise role of RACK1 in any hormone signalling pathway remains elusive. Molecular and genetic evidence that Arabidopsis RACK1 is a negative regulator of ABA responses is provided here. It is shown that three RACK1 genes act redundantly to regulate ABA responses in seed germination, cotyledon greening and root growth, because rack1a single and double mutants are hypersensitive to ABA in each of these processes. On the other hand, plants overexpressing RACK1A displayed ABA insensitivity. Consistent with their proposed roles in seed germination and early seedling development, all three RACK1 genes were expressed in imbibed, germinating and germinated seeds. It was found that the ABA-responsive marker genes, RD29B and RAB18, were up-regulated in rack1a mutants. Furthermore, the expression of all three RACK1 genes themselves was down-regulated by ABA. Consistent with the view that RACK1 negatively regulates ABA responses, rack1a mutants lose water significantly more slowly from the rosettes and are hypersensitive to high concentrations of NaCl during seed germination. In addition, the expression of some putative RACK1-interacting, ABA-, or abiotic stress-regulated genes was mis-regulated in rack1a rack1b double mutants in response to ABA. Taken together, these findings provide compelling evidence that RACK1 is a critical, negative regulator of ABA responses.

Show MeSH
Quantitative RT-PCR analysis of the expression of selected putative RACK1 interactors in response to ABA. The transcript levels of At1g54510 (ATNEK1), At2g35940 (EDA29), At3g24080, At4g23570 (SGT1A), At4g27560, At5g03730 (CTR1), At5g08415, and At5g08420 in wild-type (Col) and rack1a rack1b double mutants with ABA treatment (50 μM for 2 h), compared with no ABA treatment, were analysed by quantitative RT-PCR. The expression of ACTIN2 was used as control. The transcript level of each gene was normalized against that in Col without ABA treatment, with the value of the first biological replicate set as 1. Shown are the mean values of three biological replicates ±SE.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC2736894&req=5

fig11: Quantitative RT-PCR analysis of the expression of selected putative RACK1 interactors in response to ABA. The transcript levels of At1g54510 (ATNEK1), At2g35940 (EDA29), At3g24080, At4g23570 (SGT1A), At4g27560, At5g03730 (CTR1), At5g08415, and At5g08420 in wild-type (Col) and rack1a rack1b double mutants with ABA treatment (50 μM for 2 h), compared with no ABA treatment, were analysed by quantitative RT-PCR. The expression of ACTIN2 was used as control. The transcript level of each gene was normalized against that in Col without ABA treatment, with the value of the first biological replicate set as 1. Shown are the mean values of three biological replicates ±SE.

Mentions: Then, the ABA induction of these eight genes was examined in rack1a rack1b double mutant seedlings and compared with that in the wild type. Among these eight genes, the transcript levels of two genes, At1g54510 (ATNEK1) and At3g24080, were reduced in response to ABA in the rack1a rack1b mutant background, compared with the wild type (Fig. 11). The transcript levels of five genes, At2g35940 (EDA29), At4g23570 (SGT1A), At5g03730 (CTR1), At5g08415, and At5g08420 were increased in response to ABA in the rack1 rack1b mutant background (Fig. 11). One gene, At4g27560, responded to ABA similarly in the wild type and in rack1a-1 rack1b-2 mutant background (Fig. 11). The alternation of ABA responses of these genes in the rack1a rack1b mutant background implied that RACK1 may be involved in the ABA signalling route towards induction of these genes.


RACK1 is a negative regulator of ABA responses in Arabidopsis.

Guo J, Wang J, Xi L, Huang WD, Liang J, Chen JG - J. Exp. Bot. (2009)

Quantitative RT-PCR analysis of the expression of selected putative RACK1 interactors in response to ABA. The transcript levels of At1g54510 (ATNEK1), At2g35940 (EDA29), At3g24080, At4g23570 (SGT1A), At4g27560, At5g03730 (CTR1), At5g08415, and At5g08420 in wild-type (Col) and rack1a rack1b double mutants with ABA treatment (50 μM for 2 h), compared with no ABA treatment, were analysed by quantitative RT-PCR. The expression of ACTIN2 was used as control. The transcript level of each gene was normalized against that in Col without ABA treatment, with the value of the first biological replicate set as 1. Shown are the mean values of three biological replicates ±SE.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2736894&req=5

fig11: Quantitative RT-PCR analysis of the expression of selected putative RACK1 interactors in response to ABA. The transcript levels of At1g54510 (ATNEK1), At2g35940 (EDA29), At3g24080, At4g23570 (SGT1A), At4g27560, At5g03730 (CTR1), At5g08415, and At5g08420 in wild-type (Col) and rack1a rack1b double mutants with ABA treatment (50 μM for 2 h), compared with no ABA treatment, were analysed by quantitative RT-PCR. The expression of ACTIN2 was used as control. The transcript level of each gene was normalized against that in Col without ABA treatment, with the value of the first biological replicate set as 1. Shown are the mean values of three biological replicates ±SE.
Mentions: Then, the ABA induction of these eight genes was examined in rack1a rack1b double mutant seedlings and compared with that in the wild type. Among these eight genes, the transcript levels of two genes, At1g54510 (ATNEK1) and At3g24080, were reduced in response to ABA in the rack1a rack1b mutant background, compared with the wild type (Fig. 11). The transcript levels of five genes, At2g35940 (EDA29), At4g23570 (SGT1A), At5g03730 (CTR1), At5g08415, and At5g08420 were increased in response to ABA in the rack1 rack1b mutant background (Fig. 11). One gene, At4g27560, responded to ABA similarly in the wild type and in rack1a-1 rack1b-2 mutant background (Fig. 11). The alternation of ABA responses of these genes in the rack1a rack1b mutant background implied that RACK1 may be involved in the ABA signalling route towards induction of these genes.

Bottom Line: It was found that the ABA-responsive marker genes, RD29B and RAB18, were up-regulated in rack1a mutants.Consistent with the view that RACK1 negatively regulates ABA responses, rack1a mutants lose water significantly more slowly from the rosettes and are hypersensitive to high concentrations of NaCl during seed germination.Taken together, these findings provide compelling evidence that RACK1 is a critical, negative regulator of ABA responses.

View Article: PubMed Central - PubMed

Affiliation: Department of Botany, University of British Columbia, Vancouver, BC, Canada.

ABSTRACT
Receptor for Activated C Kinase 1 (RACK1) is viewed as a versatile scaffold protein in mammals. The protein sequence of RACK1 is highly conserved in eukaryotes. However, the function of RACK1 in plants remains poorly understood. Accumulating evidence suggested that RACK1 may be involved in hormone responses, but the precise role of RACK1 in any hormone signalling pathway remains elusive. Molecular and genetic evidence that Arabidopsis RACK1 is a negative regulator of ABA responses is provided here. It is shown that three RACK1 genes act redundantly to regulate ABA responses in seed germination, cotyledon greening and root growth, because rack1a single and double mutants are hypersensitive to ABA in each of these processes. On the other hand, plants overexpressing RACK1A displayed ABA insensitivity. Consistent with their proposed roles in seed germination and early seedling development, all three RACK1 genes were expressed in imbibed, germinating and germinated seeds. It was found that the ABA-responsive marker genes, RD29B and RAB18, were up-regulated in rack1a mutants. Furthermore, the expression of all three RACK1 genes themselves was down-regulated by ABA. Consistent with the view that RACK1 negatively regulates ABA responses, rack1a mutants lose water significantly more slowly from the rosettes and are hypersensitive to high concentrations of NaCl during seed germination. In addition, the expression of some putative RACK1-interacting, ABA-, or abiotic stress-regulated genes was mis-regulated in rack1a rack1b double mutants in response to ABA. Taken together, these findings provide compelling evidence that RACK1 is a critical, negative regulator of ABA responses.

Show MeSH