Abstract
High levels of salinity induce serious oxidative damage in plants. Flavonoids, as antioxidants, have important roles in reactive oxygen species (ROS) scavenging. In the present study, the tobacco R2R3 MYB type repressor, NtMYB4, was isolated and characterized. The expression of NtMYB4 was suppressed by salinity. Overexpression of NtMYB4 reduced the salt tolerance in transgenic tobacco plants. NtMYB4 repressed the promoter activity of NtCHS1 and negatively regulated its expression. Rutin accumulation was significantly decreased in NtMYB4 overexpressing transgenic plants and NtCHS1 RNAi silenced transgenic plants. Moreover, high H2O2 and contents were detected in both types of rutin-reduced transgenic plants under high salt stress. In addition, exogenous rutin supplementation effectively scavenged ROS (H2O2 and ) and improved the salt tolerance of the rutin-reduced transgenic plants. In contrast, NtCHS1 overexpressing plants had increased rutin accumulation, lower H2O2 and contents, and higher tolerance to salinity. These results suggested that tobacco NtMYB4 acts as a salinity response repressor and negatively regulates NtCHS1 expression, which results in the reduced flavonoid accumulation and weakened ROS-scavenging ability under salt stress.
Highlights
Salinity is one of the most significant abiotic stresses affecting plant growth and agricultural productivity
The result indicated that NtMYB4 clustered with AtMYB4, AtMYB7, and AtMYB32 (Figure 1B), which are members of subgroup 4 and repressors of the phenylpropanoid pathway
Under salt treatment, the root length was significantly reduced in all transgenic lines with respect to wild type (WT) plants (Figures 2E,F). These results showed that overexpression of NtMYB4 reduced the seed germination rate and root elongation under 200 mM NaCl compared to WT, which indicated that NtMYB4 plays a negative role in plant salt tolerance
Summary
Salinity is one of the most significant abiotic stresses affecting plant growth and agricultural productivity. The response of plants to salinity is a complex set of traits that involves signaling and metabolic processes at molecular, cellular, and whole-plant levels. Extensive research has been carried out on the mechanisms of plant salt tolerance, including ion homeostasis, osmotic adjustment, reactive oxygen species (ROS) scavenging, detoxification, signal transduction, transcription, and crosstalk with other stresses (Tuteja, 2007; Zhang et al, 2012; Deinlein et al, 2014). The detailed mechanism underlying plant salt tolerance is unclear. The exposure of plants to salinity results in massive changes in gene expression. Transcription factors (TFs) are initially vital in sensing salt and stimulating tolerance responses
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