Genome-Wide Identification and Expression Analysis of the bHLH Transcription Factor Family in Wintersweet (Chimonanthus praecox)

Abstract

Wintersweet (Chimonanthus praecox (L.) Link, Calycanthaceae) is an esteemed ornamental flowering shrub known for its distinct blooming period in winter, vibrant color petals, and captivating floral fragrance. Basic helix-loop-helix (bHLH) transcription factors (TFs) play pivotal roles as key regulators in secondary metabolites biosynthesis, growth, and development in plants. However, the systematic analysis of the bHLH family members and their role in the regulation of floral traits in Wintersweet remains insufficiently understood. To bridge this knowledge gap, we conducted a comprehensive genome-wide analysis of the C. praecox bHLH (CpbHLH) gene family, identifying a total of 131 CpbHLH genes across 11 chromosomes. Phylogenetic analysis classified these CpbHLH genes into 23 subfamilies, wherein most members within the same subfamily exhibited analogous intron/exon patterns and motif composition. Moreover, the expansion of the CpbHLH gene family was primarily driven by segmental duplication, with duplicated gene pairs experiencing purifying selection during evolution. Transcriptomic analysis revealed diverse expression patterns of CpbHLH genes in various tissues and distinct stages of Wintersweet flower development, thereby suggesting their involvement in a diverse array of physiological processes. Furthermore, yeast 2-hybrid assay demonstrated interaction between CpbHLH25 and CpbHLH59 (regulators of floral scent and color) as well as with CpbHLH112 and CpMYB2, suggesting potential coordinately regulation of secondary metabolites biosynthesis in Wintersweet flowers. Collectively, our comprehensive analysis provides valuable insights into the structural attributes, evolutionary dynamics, and expression profiles of the CpbHLH gene family, laying a solid foundation for further explorations of the multifaceted physiological and molecular roles of bHLH TFs in Wintersweet.

Unveiling the aesthetic secrets: exploring connections between genetic makeup, chemical, and environmental factors for enhancing/improving the color and fragrance/aroma of Chimonanthus praecox

“…The ontogeny of flowers in Chimonanthus praecox unfolds in a distinctive and intriguing pattern ( Shang et al, 2020 ). The flowering process is marked by intricate stages, from initiation to full bloom ( Kamran et al, 2023 ). Notably, flower initiation in Chimonanthus praecox takes place in spring, yet the blooms grace the plant during the winter months, typically from late December to January.…”

“…Notably, flower initiation in Chimonanthus praecox takes place in spring, yet the blooms grace the plant during the winter months, typically from late December to January. This unique timing is particularly remarkable as the flowering period is synchronized with seasonal climate changes, primarily responding to temperature fluctuations ( Kamran et al, 2023 ). Throughout the summer and autumn, flower buds undergo a slow growth phase, completing the specification, differentiation, and maturation of floral organs, following a pattern observed in many long-lived trees ( Kubitzki, 1993 ).…”

“…Furthermore, wintersweet flowers exhibit an entirely petaloid perianth without differentiation of sepals and petals ( Kamran et al, 2023 ). This distinctive characteristic not only adds to the ornamental appeal of the plant but also provides researchers with a unique system for elucidating various aspects of flowering-time regulation, flower development, floral bud dormancy, and bud break ( Shang et al, 2020 ).…”

“…Genetic factors play a pivotal role in determining flower color and fragrance in Chimonanthus praecox . Specific genes control pigment synthesis and the production of volatile compounds responsible for fragrance ( Kamran et al, 2023 ). The unique blooming season of wintersweet suggests distinct molecular mechanisms governing flower development compared to spring-blooming plants, highlighting the importance of understanding the genetic makeup ( Zhang et al, 2011 ; Liu et al, 2014 ).…”

“…The unique blooming season of wintersweet suggests distinct molecular mechanisms governing flower development compared to spring-blooming plants, highlighting the importance of understanding the genetic makeup ( Zhang et al, 2011 ; Liu et al, 2014 ). Genetic variations among different cultivars result in the diverse range of colors and scents observed in Chimonanthus praecox ( Shen et al, 2021 ; Kamran et al, 2023 ).…”