ABSTRACT: High salinity is one of the major environmental factors, which hampers plant growth, development and productivity. To better understand the regulatory mechanisms by which plants cope with salt stress, we used genetic approaches to identify salt hypersensitive mutant 9 (sahy9), a new allele of apum23, in Arabidopsis thaliana. The sahy9/apum23 mutant seedlings display postgemination developmental arrest and later become bleached under agar plates supplemented with various salt stressors. Transcriptomic and proteomic analyses of the salt-treated sahy9/apum23 and wild-type seedlings revealed differential expression of genes with similar functional categories, primarily including cellular and metabolic processes, and abiotic and biotic stress responses. However, the consistency of gene expression at both transcript and protein levels is low (), suggesting the involvement of posttranscriptional processing in salt response. Furthermore, the altered gene/protein expression mediated by SAHY9/APUM23 in salt sensitivity is involved in several functional groups, particularly in ABA biosynthesis and signaling, abiotic stress response, LEA proteins, and ribosome biogenesis-related genes. Importantly, NCED3, a key gene involved in ABA biosynthesis, and major ABA responsive marker genes, such as RD20 and RD29B, are down-regulated at both transcript and protein levels in sahy9/apum23 under salt stress. Consistently, lower contents of ABA and proline, and expression changes of a subset of LEA proteins also support the nature of sahy9/apum23 showing salt hypersensitivity. Collectively, these data suggest that SAHY9/APUM23-mediated salt response is associated with ABA signaling pathway and its downstream stress responsive or tolerant genes.
