Abstract
The receptor for activated C kinase 1 (RACK1) is a WD40 type protein that is involved in multiple signaling pathways and is conserved from prokaryotes to eukaryotes. Here we report that rice RACK1A (OsRACK1A) is regulated by circadian clocks and plays an important role in the salt stress response. OsRACK1A was found to follow a rhythmic expression profile under circadian conditions at both the transcription and the translation levels, although the expression was arrhythmic under salt stress. Analysis of plant survival rates, fresh weight, proline content, malondialdehyde, and chlorophyll showed that suppression of OsRACK1A enhanced tolerance to salt stress. The ion concentration in both roots and leaves revealed that OsRACK1A-suppressed transgenic rice could maintain low Na+ and high K+ concentrations. Furthermore, OsRACK1A-suppressed transgenic rice accumulated significantly more abscisic acid (ABA) and more transcripts of ABA- and stress-inducible genes compared with the wild-type plants. Real-time quantitative polymerase chain reaction analysis revealed that many stress-related genes, including APETALA 2/Ethylene Responsive Factor (AP2/ERF) transcription factors, were upregulated in the OsRACK1A-suppressed transgenic rice line. We identified putative interactors of OsRACK1A, and found that OsRACK1A interacted with many salt stress-responsive proteins directly. These results suggest that OsRACK1A is regulated by circadian rhythm, and involved in the regulation of salt stress responses.
Highlights
The receptor for activated C kinase 1 (RACK1) is a member of the WD repeat-containing scaffold proteins and is conserved from prokaryotes to eukaryotes (Zhang et al, 2013)
We examined levels of OsRACK1A protein during the light/dark cycle using western blot analysis and the results revealed that OsRACK1A protein accumulated in the light (ZT0 to ZT14) and declined in the dark (ZT16 to ZT22, Fig. 1b)
OsRACK1A significantly changes expression of salt stressrelated genes in rice plants we evaluated the expression of stress-related genes in non-transgenic line (NTL), OeTL3–8, and RiTL4–2 plants grown under both control and salt-stress conditions by real-time Quantitative PCR (qPCR)
Summary
The receptor for activated C kinase 1 (RACK1) is a member of the WD repeat-containing scaffold proteins and is conserved from prokaryotes to eukaryotes (Zhang et al, 2013). Rack1a mutants were hypersensitive to ABA in serval developmental processes, such as seed germination, cotyledon greening, and root growth, and some ABA-responsive marker genes were upregulated in rack1a mutants, while the RACK1 genes were downregulated by ABA (Guo et al, 2009). These results suggest that RACK1 functions as a negative regulator of ABA signaling and enhances drought stress tolerance via ABA-dependent signaling in response to water stress in plants. Comparative proteomic analysis showed that the Arabidopsis RACK1C protein might play roles in regulating plant resistance to salt stress (Shi et al, 2011)
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