Maize is grown under a wide spectrum of soil and climatic conditions. Maize is moderately sensitive to salt stress; therefore, soil salinity is a serious threat to its production worldwide. Understanding maize response to salt stress and resistance mechanisms and overviewing management options may help to devise strategies for improved maize performance in saline environments. Here, we reviewed the effects, resistance mechanisms, and management of salt stress in maize. Our main conclusions are as follows: (1) germination and stand establishment are more sensitive to salt stress than later developmental stages. (2) High rhizosphere sodium and chloride decrease plant uptake of nitrogen, potassium, calcium, magnesium, and iron. (3) Reduced grain weight and number are responsible for low grain yield in maize under salt stress. Sink limitations and reduced acid invertase activity in developing grains is responsible for poor kernel setting under salt stress. (4) Exclusion of excessive sodium or its compartmentation into vacuoles is an important adaptive strategy for maize under salt stress. (5) Apoplastic acidification, required for cell wall extensibility, is an important indicator of salt resistance, but not essential for better maize growth under salt stress. (6) Upregulation of antioxidant defense genes and β-expansin proteins is important for salt resistance in maize. (7) Arbuscular mycorrhizal fungi improve salt resistance in maize due to better plant nutrient availability. (8) Seed priming is an effective approach for improving maize germination under salt stress. (9) Integration of screening, breeding and ion homeostasis mechanisms into a functional paradigm for the whole plant may help to enhance salt resistance in maize.

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Ehrlichia chaffeensis is an obligately intracellular bacterium that exhibits tropism for mononuclear phagocytes and survives by evading host cell defense mechanisms. Recently, molecular interactions between E. chaffeensis 47-kDa tandem repeat (TR) protein (TRP47) and the eukaryotic host cell have been described. In this investigation, yeast (Saccharomyces cerevisiae) two-hybrid analysis demonstrated that E. chaffeensis-secreted tandem repeat protein 120 (TRP120) interacts with a diverse group of host cell proteins associated with major biological processes, including transcription and regulation, cell signaling, protein trafficking, and actin cytoskeleton organization. Twelve target proteins with the highest frequency of interaction with TRP120 were confirmed by cotransformation in yeast. Host targets, including human immunoglobulin lambda locus (IGL), cytochrome c oxidase subunit II (COX2), Golgi-associated gamma adaptin ear-containing ARF binding protein 1 (GGA1), polycomb group ring finger 5 (PCGF5), actin gamma 1 (ACTG1), and unc-13 homolog D (UNC13D; Caenorhabditis elegans), colocalized strongly with TRP120 in HeLa cells and with E. chaffeensis dense-cored morulae and areas adjacent to morulae in the host cytoplasm. The TR domain of TRP120 interacted only with PCGF5, indicating that distinct TRP120 domains contribute to specific host target interactions and that multiple domains are required to reconstitute TRP120 interactions with other host targets. Three previously defined molecular interactions between TRP47 and host proteins, PCGF5, IGLL1, and CAP1, were also associated with TRP120, demonstrating that molecular cross talk occurs between Ehrlichia TRPs and host targets. These findings further support the role of TRPs as effectors that reprogram the host cell.

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Ehrlichiae are obligately intracellular bacteria that reside and replicate in phagocytes by circumventing host cell defenses and modulating cellular processes, including host cell gene transcription. However, the mechanisms by which ehrlichiae influence host gene transcription have largely remained undetermined. Numerous ankyrin and tandem repeat-containing proteins associated with host-pathogen interactions have been identified in Ehrlichia species, but their roles in pathobiology are unknown. In this study, we determined by confocal immunofluorescence microscopy and by immunodetection in purified nuclear extracts that the ankyrin repeat-containing protein p200 is translocated to the nuclei of Ehrlichia-infected monocytes. Chromatin immunoprecipitation (ChIP) with DNA sequencing revealed an Ehrlichia chaffeensis p200 interaction located within host promoter and intronic Alu-Sx elements, the most abundant repetitive elements in the human genome. A specific adenine-rich (mid-A-stretch) motif within Alu-Sx elements was identified using electrophoretic mobility shift and NoShift assays. Whole-genome analysis with ChIP and DNA microarray analysis (ChIP-chip) determined that genes (n ‫؍‬ 456) with promoter Alu elements primarily related to transcription, apoptosis, ATPase activity, and structural proteins associated with the nucleus and membrane-bound organelles were the primary targets of p200. Several p200 target genes (encoding tumor necrosis factor alpha, Stat1, and CD48) associated with ehrlichial pathobiology were strongly upregulated during infection, as determined by quantitative PCR. This is the first study to identify a nuclear translocation of bacterially encoded protein by E. chaffeensis and to identify a specific binding motif and genes that are primary targets of a novel molecular strategy to reprogram host cell gene expression to promote survival of the pathogen.Ehrlichia chaffeensis and Ehrlichia canis are obligately intracellular bacteria that reside and replicate within cytoplasmic vacuoles in mononuclear phagocytes. Ehrlichiae are maintained in nature by persistent infection of vertebrate hosts and are transmitted by arthropods (ticks), and thus, their existence requires adaptation to host-specific environments and evasion of both innate and adaptive immune mechanisms (48,49,53).