Abstract
Cytokinin is a critical growth regulator for various aspects of plant growth and development. In Arabidopsis, cytokinin signaling is mediated by a two-component system-based phosphorelay that transmits a signal from the receptors, through histidine phosphotransfer proteins, to the downstream response regulators (ARRs). Of these ARRs, type-A ARR genes, whose transcription can be rapidly induced by cytokinin, act as negative regulators of cytokinin signaling. However, because of functional redundancy, the function of type-A ARR genes in plant growth and development is not well understood by analyzing loss-of-function mutants. In this study, we performed a comparative functional study on all ten type-A ARR genes by analyzing transgenic plants overexpressing these ARR genes fused to a MYC epitope tag. Overexpression of ARR genes results in a variety of cytokinin-associated phenotypes. Notably, overexpression of different ARR transgenes causes diverse phenotypes, even between phylogenetically closely-related gene pairs, such as within the ARR3-ARR4 and ARR5-ARR6 pairs. We found that the accumulation of a subset of ARR proteins (ARR3, ARR5, ARR7, ARR16 and ARR17; possibly ARR8 and ARR15) is increased by MG132, a specific proteasomal inhibitor, indicating that stability of these proteins is regulated by proteasomal degradation. Moreover, similar to that of previously characterized ARR5, ARR6 and ARR7, stability of ARR16 and ARR17, possibly including ARR8 and ARR15, is regulated by cytokinin. These results suggest that type-A ARR proteins are regulated by a combinatorial mechanism involving both the cytokinin and proteasome pathways, thereby executing distinctive functions in plant growth and development.
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Acknowledgements
We thank Dr Joe Kieber (University of North Carolina, USA) and the Arabidopsis Biological Resource Center (Ohio State University) for providing seeds. We thank Dr Shuhua Yang (China Agricultural University) for critically reading the manuscript. This work was supported by grants from the National Natural Science Foundation of China (90817107), the Ministry of Science and Technology of China (2007CB948203) and Chinese Academy of Sciences (KSCX2-YW-N-015).
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Supplementary information
Supplementary information, Figure S1
Primary root length of type-A ARR-OX transgenic plants. (PDF 77 kb)
Supplementary information, Figure S2
The flowering phenotype of the type-A ARR-OX plants. (PDF 62 kb)
Supplementary information, Figure S3
Reduced cytokinin sensitivity of type-A ARR-OX plants in the inhibition of primary root elongation. (PDF 81 kb)
Supplementary information, Figure S4
Root xylem development in ARR-OX and arr3,4,5,6,8,9 mutant plants. (PDF 98 kb)
Supplementary information, Figure S5
In vitro shoot formation of type-A ARR-OX hypocotyl explants. (PDF 98 kb)
Supplementary information, Figure S6
Analysis of A RR4-MYC and AR R5-MYC proteins. (PDF 72 kb)
Supplementary information, Figure S7
Stability of ARR-MYC proteins is regulated by cytokinin and MG132. (PDF 142 kb)
Supplementary information, Table 1
Primers used in this study (PDF 26 kb)
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Ren, B., Liang, Y., Deng, Y. et al. Genome-wide comparative analysis of type-A Arabidopsis response regulator genes by overexpression studies reveals their diverse roles and regulatory mechanisms in cytokinin signaling. Cell Res 19, 1178–1190 (2009). https://doi.org/10.1038/cr.2009.88
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DOI: https://doi.org/10.1038/cr.2009.88
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