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.

As a magnoliid angiosperm, the Liriodendron chinense (Hamsl) Sarg in the Magnoliaceae family is susceptible to external environmental factors. The TEOSINTE BRANCHED 1/CYCLOIDEA/PROLIFERATING CELL FACTORS (TCP) proteins known for their growth and developmental biological roles have been identified in various plant species but not in the Liriodendron chinense. In this study, 15 TCP genes were identified in the L. chinense genome, and categorized into two classes, termed class I (PCF) and class II (CIN and CYC/TB1). A total of 14 TCP genes were located on the 10 chromosomes, and the remaining one, on a contig. Multispecies phylogenetic tree analysis supported the classification of identified LcTCP genes and exhibited that the expansion of the LcTCP gene family was before the angiosperm evolutionary divergence times. Additional gene duplication investigations revealed a purifying selection pressure during evolution history. Moreover, the LcTCP genes were also observed to have various cis-acting elements related to plant growth and development, phytohormone regulations, and abiotic stress responses. Gene expression pattern analysis also paraded that LcTCP genes play a crucial role in abiotic stress regulations. In particular, LcTCP1 in all stresses investigated. Overall, our findings suggest a pivotal role for the TCP gene family during external environmental stresses in L. chinense. This study will provide valuable information on the identification and function of the LcTCPs during abiotic stresses, paving the way for further research on the functional verification of L. chinense TCPs.

Background: The sucrose non-fermenting 1 (SNF1)-related protein kinases (SnRKs) play a vivid role in regulating plant metabolism and stress response, providing a pathway for regulation between metabolism and stress signals. Conducting identification and stress response studies on SnRKs in plants contributes to the development of strategies for tree species that are more tolerant to stress conditions. Results: In the present study, a total of 30 LcSnRKs were identified in Liriodendron chinense (L. chinense) genome, which was distributed across 15 chromosomes and 4 scaffolds. It could be divided into three subfamilies: SnRK1, SnRK2, and SnRK3 based on phylogenetic analysis and domain types. The LcSnRK of the three subfamilies shared the same Ser/Thr kinase structure in gene structure and motif composition, while the functional domains, except for the kinase domain, showed significant differences. A total of 13 collinear gene pairs were detected in L. chinense and Arabidopsis thaliana (A. thaliana), and 18 pairs were detected in L. chinense and rice, suggesting that the LcSnRK family genes may be evolutionarily more closely related to rice. Cis-regulation element analysis showed that LcSnRKs were LTR and TC-rich, which could respond to different environmental stresses. Furthermore, the expression patterns of LcSnRKs are different at different times under low-temperature stress. LcSnRK1s expression tended to be down-regulated under low-temperature stress. The expression of LcSnRK2s tended to be up-regulated under low-temperature stress. The expression trend of LcSnRK3s under low-temperature stress was mainly up-or down-regulated. Conclusion: The results of this study will provide valuable information for the functional identification of the LcSnRK gene in the future.

The hyperosmolality-gated calcium-permeable channels (OSCA) play an imperative role in the plant response to environmental stresses. Moreover, their characteristics in the ornamental woody plant Liriodendron chinense, widely dispersed in the southern region of China, is yet to be elucidated. In the present study, 399 OSCA proteins were identified from 31 plant genomes, and comparative phylogenetic analysis revealed that LchiOSCAs gene family is closely related to the Magnolia Cinnamomum kanehirae OSCAs. In L. chinense, 11 LchiOSCA genes were identified and distributed across eight chromosomes. Additionally, phylogenetic analysis of LchiOSCAs exhibited a classification into four subfamilies based on the tree arrangement, similarity in the gene structures, and conserved motif numbers and order. Gene duplication investigations were biased towards the tandem duplication events, accounting for 36% (4/11) of the LchiOSCA gene family. The interspecies collinearity analysis revealed a closer relationship between the L. chinense OSCAs and the P. trichocarpa OSCAs. Analysis in promoter regions of the LchiOSCAs showed the presence of multiple phytohormones and stress responsive elements. Specifically, the ABA-responsive elements had the greatest representation. 3D protein structures of the modeled L. chinense OSCAs exhibited a high homology with the template structures, providing a better understanding of LchiOSCAs’ functionality at the proteome level. The expression pattern analysis of LchiOSCAs based on the transcriptome data and qRT-PCR in L. chinense leaves showed differential responses to drought, cold, and heat stress at varying degrees. Specifically, LchiOSCA2 and LchiOSCA4 were highly expressed under the three abiotic stresses. This research will provide valuable resources and further the understanding of plant OSCA genes in L. chinense for agronomic breeding and bio-engineering purposes.