An Enhancer Mutant of Arabidopsis salt overly sensitive 3 Mediates both Ion Homeostasis and the Oxidative Stress Response

Abstract

The myristoylated calcium sensor SOS3 and its interacting protein kinase, SOS2, play critical regulatory roles in salt tolerance. Mutations in either of these proteins render Arabidopsis thaliana plants hypersensitive to salt stress. We report here the isolation and characterization of a mutant called enh1-1 that enhances the salt sensitivity of sos3-1 and also causes increased salt sensitivity by itself. ENH1 encodes a chloroplastlocalized protein with a PDZ domain at the N-terminal region and a rubredoxin domain in the C-terminal part. Rubredoxins are known to be involved in the reduction of superoxide in some anaerobic bacteria. The enh1-1 mutation causes enhanced accumulation of reactive oxygen species (ROS), particularly under salt stress. ROS also accumulate to higher levels in sos2-1 but not in sos3-1 mutants. The enh1-1 mutation does not enhance sos2-1 phenotypes. Also, enh1-1 and sos2-1 mutants, but not sos3-1 mutants, show increased sensitivity to oxidative stress. These results indicate that ENH1 functions in the detoxification of reactive oxygen species resulting from salt stress by participating in a new salt tolerance pathway that may involve SOS2 but not SOS3.

Genomic insights into salt adaptation in a desert poplar

“…2d). They included ENH1 (enhancer of sos3-1), which encodes a chloroplast-localized rubredoxin-like protein and has an important role in mediation of both ion homeostasis and reactive oxygen species detoxification 30 ; CIPK1 (CBL-interacting protein kinase 1), a protein kinase interacting strongly with the calcium sensors CBL1 and CBL9, and alternatively controlling ABA-dependent and ABA-independent stress responses in Arabidopsis 31 ; and PSD1 (phosphatidylserine decarboxylase 1) encoding a crucial enzyme catalysing production of phosphatidylethanolamine and therefore raising stress tolerance by increasing the flexibility of cell membranes 32 (Fig. 2c).…”

“…Numerous studies have been conducted on the genetic and molecular mechanisms underlying salt tolerance in plants 18,19,30,31 , and have included genomic analyses of the extremophiles Thellungiella parvula 16 and T. salsuginea 43 . However, our current understanding of these aspects of salt tolerance remains limited, especially for woody plants 22,27 .…”

Nucleoid-Enriched Proteomes in Developing Plastids and Chloroplasts from Maize Leaves: A New Conceptual Framework for Nucleoid Functions

“…Across the chloroplast, proplastid, and nucleoid samples, we identified 28 proteins involved in protein complex assembly (Supplemental Table S4), three of which were enriched in the nucleoid fractions; these are homologs of two Arabidopsis PSII assembly factors, LPA1 (Peng et al, 2006) and LPA2 (Ma et al, 2007), as well as protein ENH1, with rubredoxin and PDZ domains and a predicted transmembrane domain (Zhu et al, 2007). Like that observed for the thylakoid sorting components, the underrepresentation of protein assembly factors is consistent with the role of the nucleoid in plastid gene expression but not in posttranslational protein biogenesis steps.…”

The GreenCut2 Resource, a Phylogenomically Derived Inventory of Proteins Specific to the Plant Lineage

“…In contrast, rubredoxins have an Fe-(SCys) 4 domain and appear to play a role in the protection of cells from oxidative damage. A mutant of AtENH1 (At5g17170), which encodes a rubredoxin-like protein, exhibits elevated levels of reactive oxygen species in plastids and decreased tolerance to high salt conditions (70).…”