Functional Characterization of a Sugar Beet BvbHLH93 Transcription Factor in Salt Stress Tolerance

Abstract

The basic/helix–loop–helix (bHLH) transcription factor (TF) plays an important role for plant growth, development, and stress responses. Previously, proteomics of NaCl treated sugar beet leaves revealed that a bHLH TF, BvbHLH93, was significantly increased under salt stress. The BvbHLH93 protein localized in the nucleus and exhibited activation activity. The expression of BvbHLH93 was significantly up-regulated in roots and leaves by salt stress, and the highest expression level in roots and leaves was 24 and 48 h after salt stress, respectively. Furthermore, constitutive expression of BvbHLH93 conferred enhanced salt tolerance in Arabidopsis, as indicated by longer roots and higher content of chlorophyll than wild type. Additionally, the ectopic expression lines accumulated less Na+ and MDA, but more K+ than the WT. Overexpression of the BvBHLH93 enhanced the activities of antioxidant enzymes by positively regulating the expression of antioxidant genes SOD and POD. Compared to WT, the overexpression plants also had low expression levels of RbohD and RbohF, which are involved in reactive oxygen species (ROS) production. These results suggest that BvbHLH93 plays a key role in enhancing salt stress tolerance by enhancing antioxidant enzymes and decreasing ROS generation.

Environmental Stress and Plants

“…Salt stress induces a deep reprogramming of gene expression that is the basis for an efficient salt stress response. Wang et al [17] focus their attention to sugar beet BvbHLH93, a transcriptional factor belonging to the basic/helixloop-helix (bHLH) family that plays an important role for plant growth, development, and stress responses. The authors report that BvbHLH93 positively regulates the expression of genes for SOD (superoxide dismutase) and POD (peroxidase) genes, encoding for enzymes involved in ROS-detoxifying pathways.…”

Salt and Drought Stress Responses in Cultivated Beets (Beta vulgaris L.) and Wild Beet (Beta maritima L.)

“…It was suggested that B. vulgaris bHLH93 (BvbHLH93) gene encoding the basic/helixloop-helix (bHLH) transcription factor is involved in salt response in sugar beet plants. Overexpression of this gene in Arabidopsis increased salt tolerance by lower Na + and lipid peroxidation levels, higher activities of antioxidant enzymes, and lower transcript levels of respiratory burst oxidase homolog genes, RbohD and RbohF [46]. Sucrose Non-Fermenting-1-Related Protein Kinase 2 (SnRK2)…”

“…In an effort to understand and evaluate the alterations in beets under abiotic stresses and to identify stress-tolerant cultivars, many studies reported differential responses of beet cultivars to salt and drought at morphological, physiological, biochemical, and molecular levels [40][41][42]. Some of the findings also depicted the effects of expressing stress-responsive beet genes in heterologous genomes [43][44][45][46]. However, a comprehensive review summarizing the responses and tolerance mechanisms of cultivated beets (B. vulgaris L.) and their ancestor, wild beet (B. maritima L.), to salt and drought is lacking.…”

A whole-genome shotgun assembly for genome characterization of the common ice plant (Mesembryanthemum crystallinum L.)

“…NF-YA were targeted by 31 MIR169 loci known to integrally regulate gene expression by maintaining histone acetylation in soybean 20 , or binding to circadian rhythm-related elements, including the "CCAAT" motif in Arabidopsis 21,22 . Several miRNAtargeting transcription factors were associated with salt tolerance (HLH, SPL, HD-ZIP) [23][24][25] or CAM-type photosynthesis (WRKY, AP2, MYB, NAC) 26-28 . All target gene families were found in the protein family collection in the ice plant genome, except for SPL and lectin receptor kinase (see Supplementary Dataset S1), indicating that an antagonistic relationship between miRNAs and mRNAs underlies the stress tolerance and photosynthetic conversion mechanisms of the ice plants.…”