Differential expression analysis of flowering-related genes in stem apex tissues of flowering Chinese cabbage based on transcriptome sequencing

【Objective】The purpose of the study was to analyze and identify candidate genes and signal pathways related to the regulation of bolting and flowering of flowering Chinese cabbage based on transcriptome sequencing data， in order to explore the regulatory molecular mechanism of bolting and flowering of flowering Chinese cabbage and provide theoretical reference for the selection and breeding of flowering Chinese cabbage varieties with different maturity properties in the future. 【Method】Transcriptome sequencing was performed on stem apex tissues at both seven-leaf stage and budding stage of two flowering Chinese cabbage varieties， Siju-19 （early-maturing type） and 80 Tian Youlü （latematuring type）. Differentially expressed genes （DEGs） between different maturity properties of flowering Chinese cabbage and between different growth stages were compared. GO functional annotation and KEGG signal pathway enrichment analysis were conducted to analyze DEGs. Candidate genes and signal pathways involved in the regulation of bolting and flowering time of flowering Chinese cabbage with different maturity properties were selected by integrating FLOR-ID and UniProt databases. The reliability of transcriptome data was verified through real-time fluorescence quantitative PCR. 【Result】Transcriptome sequencing data of flowering Chinese cabbage stem apex tissues was 81.93 Gb， and 536679570 clean reads were obtained after quality control filtering. The GC content ranged from 47.24% to 47.63%， with Q20 between 97.11% and 98.00%， and Q30 between 91.97% and 94.11%. On average， 87.98% of the data were aligned to the reference genome. A total of 1965 and 6007 DEGs were identified in Siju-19 and 80 Tian Youlü during the seven-leaf stage and the budding stage， respectively. GO functional annotation results revealed that the majority of the DEGs were associated with molecular function， mainly annotated as protein dimerization activity， heme binding and tetrapyrrole binding. Followed by biological process， which was mainly annotated as small molecule metabolic process， lipid metabolic process and ion transport. In the cellular component category， the DEGs were mainly annotated as ribosomes， organelles part， chromosomes， nuclesome， protein-DNA complexes and DNA packaging complexes. The results of KEGG signal pathway enrichment analysis showed that DEGs of Sijiu-19 flowering Chinese cabbage were significantly enriched （_adj<0.05， the same below） in photosynthetic organisms pathways such ascarbon fixation ， cutin， suberin and wax biosynthesis. DEGs of 80 Tian Youlü flowering Chinese cabbage were significantly enriched in pathways such as phenylpropanoid biosynthesis， DNA replication and plant hormone signal transduction during the seven-leaf stage and the budding stage. There were 750 DEGs between Sijiu-19 and 80 Tian Youlü， 16 of which were flowering-related genes， involving the photoperiod pathway， autonomous pathway， gibberellin pathway， vernalization pathway， temperature pathway and age pathway. Some flowering-related genes showed obvious differences in expression between the two flowering Chinese cabbage varieties. The results of real-time fluorescence quantitative PCR were strongly correlated with those of transcriptome sequencing. 【Conclusion】The bolting and flowering process of flowering Chinese cabbage is regulated by key pathways such as the photoperiodic pathway， autonomous pathway and gibberellin pathway， while it is also affected by vernalization pathway， temperature pathway and age pathway. The pathways involved in the flowering regulation of two flowering Chinese cabbage varieties of different maturity are fundamentally consistent. However， the inconsistent gene responses in the flowering regulatory pathway leads to the differences in flowering time between the two flowering Chinese cabbage varieties.