The basic helix–loop–helix (bHLH) transcription factor family is the second-largest transcription factor family in plants. Members of this family are involved in the processes of growth and development, secondary metabolic biosynthesis, signal transduction, and plant resistance. Loropetalum chinense var. rubrum is a critical woody plant with higher ornamental and economic values, which has been used as ornamental architecture and traditional Chinese herbal medicine plants. However, the bHLH transcription factors in Loropetalum chinense var. rubrum (L. chinense var. rubrum) have not yet been systematically demonstrated, and their role in the biosynthesis of anthocyanin is still unclear. Here, we identified 165 potential LcbHLHs genes by using two methods, and they were unequally distributed on chromosomes 1 to 12 of the genome of L. chinense var. rubrum. Based on an evolutionary comparison with proteins from Arabidopsis and Oryza sativa, these bHLH proteins were categorized into 21 subfamilies. Most LcbHLHs in a particular subfamily had similar gene structures and conserved motifs. The Gene Ontology annotation and Cis-elements predicted that LcbHLHs had many molecular functions and were involved in processes of plant growth, including the biosynthesis of flavonoids and anthocyanins. Transcriptomic analysis revealed different expression patterns among different tissues and cultivars of L. chinense var. rubrum. Many LcbHLHs were expressed in the leaves, and only a few genes were highly expressed in the flowers. Six LcbHLHs candidate genes were identified by bioinformatics analysis and expression analysis. Further Real-time quantitative PCR analysis and protein interaction network analysis showed that LcbHLH156, which is one of the candidate proteins belonging to the IIIf subfamily, could interact with proteins related to anthocyanin synthesis. Therefore, LcbHLH156 was transiently expressed in L. chinense var. rubrum to verify its function in regulating anthocyanin synthesis. Compared with the control group, red pigment accumulation appeared at the wound after injection, and the total anthocyanin content increased at the wound of leaves. These results lay a foundation for the research of the regulation mechanism of leaf colors in L. chinense var. rubrum and also provide a basis for the function of the LcbHLH family.

Adversity stress is the main environmental factor limiting plant growth and development, including salt and other stress factors. This study delves into the adaptability and salt tolerance mechanisms of Machilus faberi Hemsl, a species with potential for cultivation in salinized areas. We subjected the plants to various salt concentrations to observe their growth responses and to assess key physiological and biochemical indicators. The results revealed that under high salt concentrations (500 and 700 mmol⁻¹/L), symptoms such as leaf yellowing, wilting, and eventual death were observed. Notably, plant height and shoot growth ceased on the 14th day of exposure. Chlorophyll content (a, b, total a + b, and the a/b ratio) initially increased but subsequently decreased under varying levels of salt stress. Similarly, the net photosynthetic rate, stomatal conductance, leaf water content, and root activity significantly declined under these conditions. Moreover, we observed an increase in malondialdehyde levels and relative conductivity, indicative of cellular damage and stress. The activity of superoxide dismutase and ascorbate peroxidase initially increased and then diminished with prolonged stress, whereas peroxidase activity consistently increased. Levels of proline and soluble protein exhibited an upward trend, contrasting with the fluctuating pattern of soluble sugars, which decreased initially but increased subsequently. In conclusion, M. faberi exhibits a degree of tolerance to salt stress, albeit with growth limitations when concentrations exceed 300 mmol⁻¹/L. These results shed light on the plant’s mechanisms of responding to salt stress and provide a theoretical foundation for its cultivation and application in salt-affected regions.

The basic helix-loop-helix (bHLH) transcription factor family is the second-largest transcription factor in plants. Members of this family are involved in the process of growth and development, secondary metabolic biosynthesis, signal transduction, and plant resistance. Loropetalum chinense var. rubrum is a critical woody plant with higher ornamental and economic values, which used as ornamental architecture and traditional Chinese herbal medicine plant. However, the bHLH transcription factor in the L. chinense var. rubrum (Loropetalum chinense var. Rubrum) have yet to be systematically demonstrated, and their role in anthocyanin biosynthesis remains secret. Here, we identified 165 potential LcbHLHs genes by two methods, and they were unequally distributed on chromosomes 1 to 12 of the L. chinense genome. Based on a phylogenetic comparison with proteins from Arabidopsis, these bHLH proteins were categorized into 21 subfamilies. Most LcbHLHs in a given subfamily had similar gene structures and conserved motifs. The gene ontology annotation and cis-elements predicted that the LcbHLHs had many molecular functions and were involved in plant growth processes, including flavonoid and anthocyanin biosynthetic processes, etc. Transcriptomic analysis revealed different expression patterns among different tissues and cultivars in L. chinense. Many LcbHLHs were expressed in leaves, and only a few genes were highly expressed in flowers. Six LcbHLH genes differentially expressed between species and periods in color variation, which may play a key role in anthocyanin synthesis. These further functional predictions of LcbHLHs were established by quantitative real-time PCR analysis and protein-protein interaction network. This study identified the six potential bHLH genes related to anthocyanin in L. chinense and created a solid framework for future research on the function and evolution of bHLHs.