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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.

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Regulation of the transcription of RACK1 by ABA. The transcript levels of RACK1 genes in wild-type (Col) with ABA treatment (10 μM for 2 h), compared with no ABA treatment, were analysed by quantitative RT-PCR. The expression of ACTIN2 was used as control. Each RACK1 gene was normalized against 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.
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fig8: Regulation of the transcription of RACK1 by ABA. The transcript levels of RACK1 genes in wild-type (Col) with ABA treatment (10 μM for 2 h), compared with no ABA treatment, were analysed by quantitative RT-PCR. The expression of ACTIN2 was used as control. Each RACK1 gene was normalized against 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: Our genetic and molecular analyses demonstrated that RACK1 negatively regulates ABA responses in the ABA-mediated inhibition of seed germination, cotyledon greening and root growth, and ABA-induced gene expression. Because the expression of some negative regulators of ABA signalling, such as Rop 10 (Zheng et al., 2002), is also negatively regulated by ABA, the possibility whether the expression of RACK1 genes themselves may be regulated by ABA was examined. Interestingly, it was found that the transcription of all three RACK1 genes was significantly down-regulated by ABA treatment in young seedlings (Fig. 8), in contrast to that in rice cell cultures or in imbibed rice seeds where RACK1A transcripts or RACK1A protein were shown to be up-regulated by ABA (Komatsu et al., 2005; Nakashima et al., 2008).


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)

Regulation of the transcription of RACK1 by ABA. The transcript levels of RACK1 genes in wild-type (Col) with ABA treatment (10 μM for 2 h), compared with no ABA treatment, were analysed by quantitative RT-PCR. The expression of ACTIN2 was used as control. Each RACK1 gene was normalized against 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

fig8: Regulation of the transcription of RACK1 by ABA. The transcript levels of RACK1 genes in wild-type (Col) with ABA treatment (10 μM for 2 h), compared with no ABA treatment, were analysed by quantitative RT-PCR. The expression of ACTIN2 was used as control. Each RACK1 gene was normalized against 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: Our genetic and molecular analyses demonstrated that RACK1 negatively regulates ABA responses in the ABA-mediated inhibition of seed germination, cotyledon greening and root growth, and ABA-induced gene expression. Because the expression of some negative regulators of ABA signalling, such as Rop 10 (Zheng et al., 2002), is also negatively regulated by ABA, the possibility whether the expression of RACK1 genes themselves may be regulated by ABA was examined. Interestingly, it was found that the transcription of all three RACK1 genes was significantly down-regulated by ABA treatment in young seedlings (Fig. 8), in contrast to that in rice cell cultures or in imbibed rice seeds where RACK1A transcripts or RACK1A protein were shown to be up-regulated by ABA (Komatsu et al., 2005; Nakashima et al., 2008).

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