Eukaryotic initiation factor 5A (eIF5A) is a small protein ubiquitously present throughout the eukaryotic kingdom. The protein was initially identified in rabbit reticulocytes as a factor involved in formation of the first peptide bond
]. EIF5A is a highly conserved protein and contains the post-translationally synthesized amino acid hypusine
]. Molecular and biochemical studies in yeast and mammalian cells demonstrated that eIF5A is synthesized as an inactive precursor that is activated by a post-translational hypusine modification that is only detected in the eIF5A protein, and consists of a two-step sequential reaction catalyzed by deoxyhypusine synthase (DHS, EC:126.96.36.199) and deoxyhypusine hydroxylase (DHH, EC188.8.131.52)
The precise cellular function of eIF5A is not fully understood. It was originally considered to be a translation initiation factor as it can stimulate methionyl-puromycin synthesis in vitro
and transiently attach to ribosomes to begin eukaryotic cellular protein synthesis. In addition, eIF5A promotes the formation of the first peptide bond at the initiation of protein synthesis
]. Recent studies have demonstrated that eIF5A dysfunction significantly decreases protein synthesis in yeast, and that eIF5A promotes translation elongation in Saccharomyces cerevisiae
]. Henderson and Hershey found that although eIF5A is not required for protein synthesis, eIF5A can stimulate the process by about 2- to 3-fold. They further draw a conclusion that the polysome profiles observe during and after eIF5A depletion are diagnostic for a role in initiation
]. In addition, eIF5A is involved in cellular proliferation and apoptosis
], promotes cell viability and cell growth
] and the synthesis of proteins involved in progression of the cell cycle
]. Moreover, eIF5A proteins are found to facilitate protein synthesis by participating in the nuclear export of specific mRNAs
]. Furthermore, eIF5A proteins also play a role in RNA binding, and contain a C-terminal domain with a structure that resembles an oligonucleotide-binding fold
Plant eIF5A proteins are also highly conserved that are involved in multiple biological processes, including protein synthesis regulation, translation elongation, mRNA turnover and decay, cell proliferation, leaf and root growth, seed yield, leaf, flower and fruit senescence and programmed cell death
]. Ma et al
. showed that eIF5A plays roles in supporting plant growth and in regulating responses to sub-lethal osmotic and nutrient stress
]. Valentini et al.
showed that eIF5A is involved in the WSC/PKC1 signaling pathway that controls cell wall integrity or related processes, and plays a role in cell wall formation
]. Hopkins et al.
reported that eIF5A plays a vital role in signal transduction pathways involved in pathogen-induced cell death and in the development of plant disease symptoms. Plant eIF5A
genes are also involved in abiotic stress responses
]. For instance, Xu et al.
showed that transgenic Arabidopsis
plants overexpressing RceIF5A
show improved resistance to heat, oxidative and osmotic stresses, while the plants with reduced eIF5A
expression (three AteIF5A
isoforms in Arabidopsis
are down-regulated) are more susceptible to these stresses
]. Chou et al.
reported that salt and heavy metal stresses induce the expression of rice eIF5A
, suggesting that they are involved in stress tolerance
However, little is known of the upstream regulators or its regulatory network, and its role in stress tolerance. In addition, if eIF5A does in fact confer stress tolerance in plants, the physiological changes mediated by eIF5A deserve further study.
Tamarix (Tamaricaceae) species, which include small trees or shrubs, are widely distributed in the saline soils of drought-stricken areas of Central Asia and China. Tamarix androssowii Litvinov is highly tolerant to abiotic stresses, such as salinity, drought and high temperatures. These characteristics make the species a suitable source of stress tolerance genes and for investigating endogenous stress resistance mechanisms.
In the present study, we cloned and functionally characterized an eIF5A from T. androssowii. We showed that TaeIF5A1 is a stress-responsive gene involved in the ABA signal transduction pathway. TaWRKY and TaRAV can active the expression of TaeIF5A1. In addition, TaeIF5A1 facilitates protein synthesis and regulates several physiological pathways to improve stress tolerance. This study reveals a physiological role for eIF5A and defines a possible mechanism for eIF5A-mediated stress tolerance in plants.