Abstract
bHLH (basic helix-loop-helix) transcription factors play important roles in the abiotic stress response in plants, but their characteristics and functions in tartary buckwheat (Fagopyrum tataricum), a flavonoid-rich cereal crop with a strong stress tolerance, have not been fully investigated. Here, a novel bHLH gene, designated FtbHLH3, was isolated and characterized. Expression analysis in tartary buckwheat revealed that FtbHLH3 was mainly induced by polyethylene glycol 6000 (PEG6000) and abscisic acid (ABA) treatments. Subcellular localization and a yeast one-hybrid assay indicated that FtbHLH3 has transcriptional activation activities. Overexpression of FtbHLH3 in Arabidopsis resulted in increased drought/oxidative tolerance, which was attributed to not only lower malondialdehyde (MDA), ion leakage (IL), and reactive oxygen species (ROS) but also higher proline (Pro) content, activities of antioxidant enzymes, and photosynthetic efficiency in transgenic lines compared to wild type (WT). Moreover, qRT-PCR analysis indicated that the expression of multiple stress-responsive genes in the transgenic lines was significantly higher than in WT under drought stress. In particular, the expression of AtNCED, a rate-limiting enzyme gene in ABA biosynthesis, was increased significantly under both normal and stress conditions. Additionally, an ABA-response-element (ABRE) was also found in the promoter regions. Furthermore, the transgenic Arabidopsis lines of the FtbHLH3 promoter had higher GUS activity after drought stress. In summary, our results indicated that FtbHLH3 may function as a positive regulator of drought/oxidative stress tolerance in transgenic Arabidopsis through an ABA-dependent pathway.
Highlights
Drought is one of the harshest environmental factors during the plant growth process, limiting plant development and crop productivity and further leading to large economic losses (Umezawa et al, 2006)
To identify putative bHLH genes that may be closely involved in the abiotic stresses, two bHLH genes AtbHLH116 and AtbHLH61 as probes were screened from the tartary buckwheat transcriptome database constructed by our laboratory
The gene (FtbHLH3) encoded a bHLH factor which was clustered with the PebHLH35 factor involved in drought stress in Populus euphratica (Dong et al, 2014)
Summary
Drought is one of the harshest environmental factors during the plant growth process, limiting plant development and crop productivity and further leading to large economic losses (Umezawa et al, 2006). Various functional proteins involved in these processes are mainly regulated by various types of transcription factors (TFs), such as the MYB, bHLH, DREB, and WRKY families. These transcription factors play crucial roles in the signaling network of plant resistance to environmental stimulation (Wang et al, 2011; Huang et al, 2012). The rice transcription factor OrbHLH2 regulated salt-stress signals independent of ABA in Arabidopsis by upregulating the expression of stress-responsive genes DREB1A/CBF3, RD29A, COR15A, and KIN1 (Zhou et al, 2009). Ectopic expression of OrbHLH001 improved the tolerance of transgenic plants to freezing and salt stresses, and the function is independent of the CBF/DREB1 cold-response pathway (Li et al, 2010). BHLH transcription factors play significant roles in the molecular mechanism of stress resistance and improve the drought resistance of crops
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