Transcriptional and Post-Translational Regulation of Plant bHLH Transcription Factors during the Response to Environmental Stresses

Abstract

Over the past decades, extensive research has been conducted to identify and characterize various plant transcription factors involved in abiotic stress responses. Therefore, numerous efforts have been made to improve plant stress tolerance by engineering these transcription factor genes. The plant basic Helix-Loop-Helix (bHLH) transcription factor family represents one of the most prominent gene families and contains a bHLH motif that is highly conserved in eukaryotic organisms. By binding to specific positions in promoters, they activate or repress the transcription of specific response genes and thus affect multiple variables in plant physiology such as the response to abiotic stresses, which include drought, climatic variations, mineral deficiencies, excessive salinity, and water stress. The regulation of bHLH transcription factors is crucial to better control their activity. On the one hand, they are regulated at the transcriptional level by other upstream components; on the other hand, they undergo various modifications such as ubiquitination, phosphorylation, and glycosylation at the post-translational level. Modified bHLH transcription factors can form a complex regulatory network to regulate the expression of stress response genes and thus determine the activation of physiological and metabolic reactions. This review article focuses on the structural characteristics, classification, function, and regulatory mechanism of bHLH transcription factor expression at the transcriptional and post-translational levels during their responses to various abiotic stress conditions.

Keywords: abiotic stress; bHLH transcription factors; post-translational regulation; transcriptional regulation.

Figure 1

(A) The crystal structure of bHLH domain heterodimer bound to the DNA. (B) The sequence logo of the bHLH domain. The overall height of each stack represents the conservation of the sequence at that position. Each color of the letters represents a type of amino acid residue. (C) The phylogenetic tree analysis of bHLH gene family in Oryza sativa [monocot]; Arabidopsis thaliana [eudicot]; Selaginella moellendorffii [lycophyte]; Physcomitrella patens [moss]; Volvox carteri; Chlamydomonas reinhardtii; Chlorella vulgaris; Ostreococcus tauri; and Cyanidioschyzon merolae was constructed using MEGA7.0 with the JTT method and 1000 replicates. Then, the trees were visualized using Figtree. Group names were marked outside the circle. The protein sequences were downloaded from the report in 2010 [1].

Figure 2

The bHLH domain conservative motif analysis expressed in different plants. Conservative domain motifs are used in MEME online web analytics. The bHLH protein sequences of these species were downloaded from the JGI and NCBI databases.

Figure 2

The bHLH domain conservative motif analysis expressed in different plants. Conservative domain motifs are used in MEME online web analytics. The bHLH protein sequences of these species were downloaded from the JGI and NCBI databases.

Figure 3

Summary of the different types of bHLH TFs responses to abiotic stresses in plants.

Figure 4

Transcriptional regulations of bHLH TF under abiotic stresses. (A) For drought stress; (B) for salt stress; (C) for cold stress; and (D) for nutrient deficiency stress.

Figure 5

Post-translational regulations of bHLH TF under abiotic stresses. (A) For drought stress; (B) for salt stress; (C) for cold stress; and (D) for nutrient deficiency stress.