Winter rapeseed (Brassica rapa L.) is an important oilseed crop in northwest China. Freezing stress severely limits its production and geographical distribution, and frequent extreme freezing events caused by climate change are increasing the chances of winter freeze-injury. However, the underlying mechanism of B. rapa response to freezing stress remains elusive. Here, B. rapa genome (v3.0) was used as a reference for the comparative transcriptomic analysis of Longyou 6 and Tianyou 2 (strong and weak cold tolerance, respectively) under different freezing stress. Before and after freezing stress, 5,982 and 11,630 unique differentially expressed genes (DEGs) between two cultivars were identified, respectively. After freezing stress, the GO terms in Tianyou 2 were mainly involved in “macromolecule biosynthetic process”, and those in Longyou 6 were involved in “response to stimulus” and “oxidoreductase activity”. Morphological and physiological results indicated that Longyou 6 retained a higher basal freezing resistance than Tinayou 2, and that cold acclimation could strengthen the basal freezing resistance. Freezing stress could activate the MAPK signal cascades, and the phosphorylation level of Longyou 6 showed a higher increase in response to freezing treatment than Tianyou 2. Based on our findings, it was speculated that the cell membrane of B. rapa perceives external signals under freezing stress, which are then transmitted to the nucleus through the cold-activated MAPK cascades and Ca²⁺-related protein kinase pathway, thus leading to activation of downstream target genes to enhance the freezing resistance of B. rapa.

The MYB (v-Myb avivan myoblastsis virus oncogene homolog) transcription factor family is one of the largest families of plant transcription factors which plays a vital role in many aspects of plant growth and development. MYB-related is a subclass of the MYB family. Fifty-nine Arabidopsis thaliana MYB-related (AtMYB-related) genes have been identified. In order to understand the functions of these genes, in this review, the promoters of AtMYB-related genes were analyzed by means of bioinformatics, and the progress of research into the functions of these genes has been described. The main functions of these AtMYB-related genes are light response and circadian rhythm regulation, root hair and trichome development, telomere DNA binding, and hormone response. From an analysis of cis-acting elements, it was found that the promoters of these genes contained light-responsive elements and plant hormone response elements. Most genes contained elements related to drought, low temperature, and defense and stress responses. These analyses suggest that AtMYB-related genes may be involved in A. thaliana growth and development, and environmental adaptation through plant hormone pathways. However, the functions of many genes do not occur independently but instead interact with each other through different pathways. In the future, the study of the role of the gene in different pathways will be conducive to a comprehensive understanding of the function of the gene. Therefore, gene cloning and protein functional analyses can be subsequently used to understand the regulatory mechanisms of AtMYB-related genes in the interaction of multiple signal pathways. This review provides theoretical guidance for the follow-up study of plant MYB-related genes.

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.