Ying Jiang

Potassium retention under saline conditions has emerged as an important determinant for salt tolerance in plants. Halophytic Hordeum brevisubulatum evolves better strategies to retain K⁺ to improve high-salt tolerance. Hence, uncovering K⁺-efficient uptake under salt stress is vital for understanding K⁺ homeostasis. HAK/KUP/KT transporters play important roles in promoting K⁺ uptake during multiple stresses. Here, we obtained nine salt-induced HAK/KUP/KT members in H. brevisubulatum with different expression patterns compared with H. vulgare through transcriptomic analysis. One member HbHAK1 showed high-affinity K⁺ transporter activity in athak5 to cope with low-K⁺ or salt stresses. The expression of HbHAK1 in yeast Cy162 strains exhibited strong activities in K⁺ uptake under extremely low external K⁺ conditions and reducing Na⁺ toxicity to maintain the survival of yeast cells under high-salt-stress. Comparing with the sequence of barley HvHAK1, we found that C170 and R342 in a conserved domain played pivotal roles in K⁺ selectivity under extremely low-K⁺ conditions (10 μM) and that A13 was responsible for the salt tolerance. Our findings revealed the mechanism of HbHAK1 for K⁺ accumulation and the significant natural adaptive sites for HAK1 activity, highlighting the potential value for crops to promote K⁺-uptake under stresses.

Key message: HbMBF1a was isolated and characterized in H. brevisubulatum, and overexpressed HbMBF1a could enhance the salt tolerance and ABA insensitivity in Arabidopsis thaliana. The transcript levels of stress-responsive genes were significantly increased in the transgenic lines under salt and ABA conditions. Salinity is an abiotic stress that considerably affects plant growth, yield, and distribution. Hordeum brevisubulatum is a halophyte that evolved to become highly tolerant to salinity. Multiprotein bridging factor 1 (MBF1) is a transcriptional coactivator and an important regulator of stress tolerance. In this study, we isolated and characterized HbMBF1a based on the transcriptome data of H. brevisubulatum grown under saline conditions. We overexpressed HbMBF1a in Arabidopsis thaliana and compared the phenotypes of the transgenic lines and the wild-type in response to stresses. The results indicated that HbMBF1a expression was induced by salt and ABA treatments during the middle and late stages. The overexpression of HbMBF1a in A. thaliana resulted in enhanced salt tolerance and ABA insensitivity. More specifically, the enhanced salt tolerance manifested as the increased seed germination and seedling growth and development. Similarly, under ABA treatments, the cotyledon greening rate and seedling root length were higher in the HbMBF1a-overexpressing lines, suggesting the transgenic plants were better adapted to high exogenous ABA levels. Furthermore, the transcript levels of stress-responsive genes were significantly increased in the transgenic lines under salt and ABA conditions. Thus, HbMBF1a is a positive regulator of salt and ABA responses, and the corresponding gene may be useful for producing transgenic plants that are salt tolerant and/or ABA insensitive, with few adverse effects. This study involved a comprehensive analysis of HbMBF1a. The results may provide the basis and insight for the application of MBF1 family genes for developing stress-tolerant crops.

Real-time quantitative PCR has been widely used as the most reliable method to measure gene expression, due to its high accuracy and specificity. Wild barley (Hordeum brevisubulatum (Trin.) Link) is a wild relative species in Triticeae that has strong tolerance to abiotic stresses and extremely wide adaptation. However, suitable references gene have not been documented for standardization of gene expression in wild barley under abiotic stress. Here we report the first systematic and comprehensive analysis of reference genes for quantitative real-time PCR standardization in wild barley. We selected 11 genes, including ACT (Actin), ADP (ADP-ribosylation factor 1), CYP2 (Cyclophilin 2), EF-1α (Elongation factor 1-alpha), GAPDH (Glyceraldehyde 3-phosphate dehydrogenase), HSP90 (Heat shock protein 90), TUBα (Alpha-tubulin), TUBβ6 (Beta-tubulin 6), UBI (Ubiquitin), 18SrRNA-1 (guanine1575-N7-methyltransferase) and 18SrRNA-3 (adenine1779-N6-dimethyltransferase) from a wild barley transcriptome database and analyzed their expression stabilities in shoots and roots of wild barley seedling under various stress conditions using comparative ΔCt, BestKeeper, Normfinder and geNorm software. The results demonstrated that ADP was the most suitable reference gene in salt stress while UBI showed peak stability under mannitol and ABA stress; EF-1α was the most appropriate reference gene for PEG, GA3, ethylene and heat stress; 18SrRNA-3 was the best choice for cold stress; and TUBα was the first stable gene across different tissues. Our main contribution was to identify reference genes with suitable and stable expression in wild barley under various stress conditions and in different tissues to provide a useful resource for future studies. The results demonstrate the importance of transcriptome data as a useful resource for the screening of candidate reference genes and highlight the need for specific reference genes for specific conditions. Furthermore, these findings will provide valuable information for wild barley and relative species for future research.

Background: The Phosphate transporter 1 (PHT1) gene family has crucial roles in phosphate uptake, translocation, remobilization, and optimization of metabolic processes using of Pi. Gene duplications expand the size of gene families, and subfunctionalization of paralog gene pairs is a predominant tendency after gene duplications. To date, experimental evidence for the evolutionary relationships among different paralog gene pairs of a given gene family in soybean is limited. Results: All potential Phosphate transporter 1 genes in Glycine max L. (GmPHT1) were systematically analyzed using both bioinformatics and experimentation. The soybean PHT1 genes originated from four distinct ancestors prior to the Gamma WGT and formed 7 paralog gene pairs and a singleton gene. Six of the paralog gene pairs underwent subfunctionalization, and while GmPHT1;4 paralog gene experienced pseudogenization. Examination of long-term evolutionary changes, six GmPHT1 paralog gene pairs diverged at multiple levels, in aspects of spatio-temporal expression patterns and/or quanta, phosphates affinity properties, subcellular localization, and responses to phosphorus stress. Conclusions: These characterized divergences occurred in tissue- and/or development-specific modes, or conditional modes. Moreover, they have synergistically shaped the evolutionary rate of GmPHT1 family, as well as maintained phosphorus homeostasis at cells and in the whole plant.