Abstract
BackgroundAlthough the nucleolus involves two major functions: pre-rRNA processing and ribosome biogenesis/assembly, increasing evidence indicates that it also plays important roles in response to abiotic stress. However, the possible regulatory mechanisms underlying the nucleolar proteins responsive to abiotic stress are largely unknown. High salinity is one of the major abiotic stresses, which hinders plant growth and productivity. Here, genetic screening approach was used to identify a salt hypersensitive mutant 9 (sahy9) mutant, also known as apum23, in Arabidopsis thaliana. Functional characterization of SAHY9/APUM23 through analyses of gene/protein expression profiles and metabolites was performed to decipher the possible regulatory mechanisms of the nucleolar protein SAHY9/APUM23 in response to salt stress.ResultsSeedlings of the sahy9/apum23 mutant displayed postgermination developmental arrest and then became bleached after prolonged culture under various salt stresses. Transcriptomic and proteomic analyses of salt-treated sahy9/apum23 and wild-type seedlings revealed differential expression of genes/proteins that have similar functional categories of biological processes, primarily those involved in cellular and metabolic processes as well as abiotic and biotic stress responses. However, the consistency of differential gene expression at both the transcript and protein levels was low (~ 12%), which suggests the involvement of posttranscriptional processing during the salt response. Furthermore, the altered expression of genes and proteins mediated by SAHY9/APUM23 regarding salt sensitivity involves abscisic acid (ABA) biosynthesis and signaling, abiotic stress responses, and ribosome biogenesis-related genes. Importantly, NCED3, ABI2, PP2CA, and major ABA-responsive marker genes, such as RD20 and RD29B, were down-regulated at both the transcript and protein levels in conjunction with lower contents of ABA and changes in the expression of a subset of LEA proteins in sahy9/apum23 mutants under salt stress. Moreover, the salt hypersensitivity of the sahy9/apum23 mutant was largely rescued by the exogenous application of ABA during salt stress.ConclusionOur results revealed that SAHY9/APUM23 regulated the expression of ribosome biogenesis-related genes and proteins, which further affected the ribosome composition and abundance, and potential posttranscriptional regulation. The salt hypersensitivity of sahy9/apum23 is associated with the ABA-mediated signaling pathway and the downstream stress-responsive network of this pathway.
Highlights
The nucleolus involves two major functions: pre-rRNA processing and ribosome biogenesis/ assembly, increasing evidence indicates that it plays important roles in response to abiotic stress
Salt hypersensitive mutant 9 is a new allele of apum23 To identify novel components involved in the salt stress response or signaling, a genetic approach was used to screen transfer-DNA (T-DNA) insertion seed pools [27] on agar plates supplemented with 150 mM NaCl; at this concentration, wild-type seeds can grow, but salt-hypersensitive seeds display postgermination developmental arrest and yield bleached seedlings at subsequent growth stages
To further confirm whether the sahy9/ apum23 mutant phenotype was due to mutation of the APUM23 gene, we requested another allelic mutant line, SALK_052992, known as apum23–2 [23], from the Arabidopsis Biological Resource Center (ABRC, OH)
Summary
The nucleolus involves two major functions: pre-rRNA processing and ribosome biogenesis/ assembly, increasing evidence indicates that it plays important roles in response to abiotic stress. High salinity is one of the major abiotic stresses, which hinders plant growth and productivity. Functional characterization of SAHY9/APUM23 through analyses of gene/protein expression profiles and metabolites was performed to decipher the possible regulatory mechanisms of the nucleolar protein SAHY9/APUM23 in response to salt stress. Numerous gene functions in salt stress responses and tolerance are induced through complex signal transduction pathways These pathways include the salt overly sensitive (SOS)-mediated pathway [1, 5, 6], abscisic acid (ABA) biosynthesis and signaling [7], secondary signals (such as reactive oxygen species [ROS] and Ca2+) [8,9,10], the production of osmotic solutes such as proline [11], and small compatible molecules such as Late Embryogenesis Abundant (LEA) proteins [12]. Great progress has been made in understanding the salt stress response in plants, the detailed regulatory mechanisms largely remain uncharacterized
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