Winter rapeseed (Brassica rapa) has a good chilling and freezing tolerance. inducer of CBF expression 1 (ICE1) plays a crucial role in cold signaling in plants; however, its role in Brassica rapa remains unclear. In this study, we identified 41 ICE1 homologous genes from six widely cultivated Brassica species. These genes exhibited high conservation, with evolutionary complexity between diploid and allotetraploid species. Cold stress induced ICE1 homolog expression, with differences between strongly and weakly cold-tolerant varieties. Two novel ICE1 paralogs, BrICE1 and BrICE2, were cloned from Brassica rapa Longyou 6. Subcellular localization assays showed that they localized to the nucleus, and low temperature did not affect their nuclear localization. The overexpression of BrICE1 and BrICE2 increased cold tolerance in transgenic Arabidopsis and enhanced reactive oxygen species’ (ROS) scavenging ability. Furthermore, our data demonstrate that overexpression of BrICE1 and BrICE2 inhibited root growth in Arabidopsis, and low temperatures could induce the degradation of BrICE1 and BrICE2 via the 26S-proteasome pathway. In summary, ICE1 homologous genes exhibit complex evolutionary relationships in Brassica species and are involved in the C-repeat/DREB binding factor (CBF) pathway and ROS scavenging mechanism in response to cold stress; these regulating mechanisms might also be responsible for balancing the development and cold defense of Brassica rapa.

Winter rapeseed (Brassica rapa) has good chilling and freezing tolerance. INDUCER OF CBF EXPRESSION1 (ICE) plays a crucial role in cold signaling in plant; however, its role in B. rapa remains unclear. In this study, we identified 41 ICE1 homologous genes from 6 widely cultivated Brassica species. These genes exhibited high conservation, with evolutionary complexity between diploid and allotetraploid species. Cold stress induced ICE1 homolog expression, with differences between strong and weak cold-tolerant varieties. Two novel ICE1 paralogs, BrICE1 and BrICE2 were cloned from B. rapa Longyou 6. Subcellular localization assays showed that they localized to the nucleus, and low temperature did not affect their nuclear localization. Overexpression of BrICE1 and BrICE2 increased cold tolerance in transgenic Arabidopsis, and enhanced reactive oxygen species (ROS) scavenging ability. Furthermore, our data demonstrate that overexpression of BrICE1 and BrICE2 inhibited root growth in Arabidopsis, and low temperatures could induce the degradation of BrICE1 and BrICE2 via the 26S-proteasome pathway. In summary, ICE1 ho-mologous genes exhibit complex evolutionary relationships in Brassica species, and are involved in the CBF pathway, and ROS scavenging mechanism in response to cold stress; these regulating mechanisms might be also responsible for balancing the development and cold defense of B. rapa.

BRI1-EMS-SUPPRESSOR 1 (BES1)/BRASSINAZOLE-RESISTANT 1 (BZR1) transcription factors serve as core regulators of brassinosteroid (BR) signal in seed plants, where they control diverse developmental processes, including cell elongation, vascular development, and environmental responses; however, their evolutionary trajectory and functional diversification in early-diverging land plants remain poorly characterized. In this study, we systematically characterized the BES1/BZR1 gene family across 12 representative bryophyte species covering hornworts, liverworts and mosses, with Arabidopsis thaliana included as a vascular plant outgroup. In total, 19 non-redundant BES1/BZR1 homologs were identified within bryophyte genomes. Phylogenetic reconstruction, synteny analysis and Ka/Ks selection pressure analyses collectively revealed that this gene family is evolutionarily conserved throughout bryophytes, with moss-specific lineage expansion; most paralogous gene pairs have experienced strong purifying selection during evolution. Further analyses of gene structural organization, conserved protein motifs and cis-acting promoter elements uncovered universally conserved core domains alongside lineage-specific structural and regulatory variations. Subcellular localization assays demonstrated that the majority of tested bryophyte BES1/BZR1 proteins primarily accumulate in the nucleus, and autoluminescent reporter assays verified that multiple homologs modulate E-box-driven transcriptional activity. Transcriptional expression profiling indicated that BES1/BZR1 genes from Marchantia polymorpha and Sphagnum fallax are transcriptionally responsive to exogenous BR treatment, while several paralogs in S. fallax additionally exhibit altered expression under drought stress. Collectively, our results demonstrate that the BES1/BZR1 family originated at an early stage of land plant evolution, followed by lineage-specific gene expansion and divergent transcriptional regulation in bryophytes. This work advances our understanding of ancestral BR signaling and stress response modules in the early terrestrial plant lineages.

Inducer of C-Repeat Binding Factor (CBF) expression (ICE), a well-known MYC-type bHLH transcription factor, plays a crucial role in the ICE-CBF-cold regulated (COR) cold signaling pathway. Brassica rapa (B. rapa), an important oilseed and vegetable crop, exhibits strong chilling and freezing tolerance. However, the exact molecular mechanisms by which ICE1 functions in B. rapa remain unclear. Here, 41 ICE1 homologous genes were identified from six widely cultivated Brassica species using a bioinformatics approach. These genes exhibit high conservation but reveal evolutionary complexity between diploid and allotetraploid species. Low-temperature stress induced ICE1 homolog expression, with patterns differing between strong and weak cold-tolerant varieties. Two novel ICE1 paralogs, BrICE1 and BrICE2, were cloned from Longyou 6. They positively regulate cold tolerance in B. rapa via a CBF-dependent pathway, contributing to reactive oxygen species (ROS) scavenfging and osmotic adjustment. Immunoblot analysis revealed that low temperatures induce BrICE1 and BrICE2 degradation via the 26S-proteasome pathway. In summary, ICE1 exhibits complex evolutionary relationships in Brassica species. BrICE1 and BrICE2 positively regulate cold tolerance via the CBF-dependent pathway and ROS scavenging mechanism and are also responsible for balancing the development and cold defense of B. rapa.