Genome-Wide Analysis of bHLH Family Genes and Identification of Members Associated with Cold/Drought-Induced Photoinhibition in Kandelia obovata

Plant basic helix-loop-helix (bHLH) transcription factors play pivotal roles in responding to stress, including cold and drought. However, it remains unclear how bHLH family genes respond to these stresses in Kandelia obovata. In this study, we identified 75 bHLH members in K. obovata, classified into 11 subfamilies and unevenly distributed across its 18 chromosomes. Collineation analysis revealed that segmental duplication primarily drove the expansion of KobHLH genes. The KobHLH promoters were enriched with elements associated with light response. Through RNA-seq, we identified several cold/drought-associated KobHLH genes. This correlated with decreased net photosynthetic rates (P(n)) in the leaves of cold/drought-treated plants. Weighted gene co-expression network analysis (WGCNA) confirmed that 11 KobHLH genes were closely linked to photoinhibition in photosystem II (PS II). Among them, four Phytochrome Interacting Factors (PIFs) involved in chlorophyll metabolism were significantly down-regulated. Subcellular localization showed that KobHLH52 and KobHLH30 were located in the nucleus. Overall, we have comprehensively analyzed the KobHLH family and identified several members associated with photoinhibition under cold or drought stress, which may be helpfulfor further cold/drought-tolerance enhancement and molecular breeding through genetic engineering in K. obovata.