Foxtail millet (Setaria italica (L.) P. Beauv) is a naturally stress tolerant crop.  Compared to other gramineous crops, it has relatively stronger drought and lower nutrition stress tolerance traits.  To date, the scope of functional genomics research in foxtail millet (S. italic L.) has been quite limited.  NAC (NAM, ATAF1/2 and CUC2)-like transcription factors are known to be involved in various biological processes, including abiotic stress responses.  In our previous foxtail millet (S. italic L.) RNA seq analysis, we found that the expression of a NAC-like transcription factor, SiNAC110, could be induced by drought stress; additionally, other references have reported that SiNAC110 expression could be induced by abiotic stress.  So, we here selected SiNAC110 for further characterization and functional analysis.  First, the predicted SiNAC110 protein encoded indicated SiNAC110 has a conserved NAM (no apical meristem) domain between the 11–139 amino acid positions.  Phylogenetic analysis then indicated that SiNAC110 belongs to subfamily III of the NAC gene family.  Subcellular localization analysis revealed that the SiNAC110-GFP fusion protein was localized to the nucleus in Arabidopsis protoplasts.  Gene expression profiling analysis indicated that expression of SiNAC110 was induced by dehydration, high salinity and other abiotic stresses.  Gene functional analysis using SiNAC110 overexpressed Arabidopsis plants indicated that, under drought and high salt stress conditions, the seed germination rate, root length, root surface area, fresh weight, and dry weight of the SiNAC110 overexpressed lines were significantly higher than the wild type (WT), suggesting that the SiNAC110 overexpressed lines had enhanced tolerance to drought and high salt stresses.  However, overexpression of SiNAC110 did not affect the sensitivity of SiNAC110 overexpressed lines to abscisic acid (ABA) treatment.  Expression analysis of genes involved in proline synthesis, Na⁺/K⁺ transport, drought responses, and aqueous transport proteins were higher in the SiNAC110 overexpressed lines than in the WT, whereas expression of ABA-dependent pathway genes did not change.  These results indicated that overexpression of SiNAC110 conferred tolerance to drought and high salt stresses, likely through influencing the regulation of proline biosynthesis, ion homeostasis and osmotic balance.  Therefore SiNAC110 appears to function in the ABA-independent abiotic stress response pathway in plants.

The heterotrimeric GTP-binding proteins (G-proteins) in eukaryotes consisted of α, β and γ subunits and are important in molecular signaling by interacting with G-protein-coupled receptors (GPCR), on which to transduce signaling into the cytoplast through appropriate downstream effectors. However, downstream effectors regulated by the G-proteins in plants are currently not well defined. In this study, the transcripts of AGB1, a G protein β subunit gene in Arabidopsis were found to be down-regulated by cold and heat, but up-regulated by high salt stress treatment. AGB1 mutant (agb1-2) was more sensitive to high salt stress than wild-type (WT). Compared with WT, the cotyledon greening rates, fresh weight, root length, seedling germination rates and survival rates decreased more rapidly in agb1-2 along with increasing concentrations of NaCl in normal (MS) medium. Physiological characteristic analysis showed that compared to WT, the contents of chlorophyll, relative proline accumulation and peroxidase (POD) were reduced, whereas the malonaldehyde (MDA) content and concentration ratio of Na+/K+ were increased in agb1-2 under salt stress condition. Further studies on the expression of several stress inducible genes associated with above physiological processes were investigated, and the results revealed that the expressions of genes related to proline biosynthesis, oxidative stress response, Na+ homeostasis, stress- and ABAresponses were lower in agb1-2 than in WT, suggesting that those genes are possible downstream genes of AGB1 and that their changed expression plays an important role in determining phenotypic and physiologic traits in agb1-2. Taken together, these findings indicate that AGB1 positively regulates salt tolerance in Arabidopsis through its modulation of genes transcription related to proline biosynthesis, oxidative stress, ion homeostasis, stress- and ABA-responses.