Time Course Transcriptomic Analysis of Cabbage (Brassica oleracea ssp. capitata L.) During Vernalization

Long-term exposure to cold during the winter season, so-called vernalization, triggers the transition from the vegetative to the reproductive stage in many biennial and perennial plants. In the last decades, intensive researches have revealed the molecular mechanisms underlying this phenomenon, particularly using Arabidopsis model plant. Most Brassicaceae family plants, including the Arabidopsis, require vernalization for floral transition. Brassicaceae family plants can be classified into two groups: seed vernalization responsive type and plant vernalization responsive type. Cabbage belongs to plant vernalization responsive type. Molecular details on plant vernalization responsive trait of cabbage on vernalization are still poorly understood. In this study, we conducted a transcriptomic analysis of the cabbage inbred line ‘BN2348’ in response to vernalization. Similar to the case of Arabidopsis, two VIN3 homologs (BoVIN3.C3 and BoVIN3.C2) were highly induced by the exposure to long-term cold in B. oleracea. Our transcriptome analysis identified that two FT homologs (BoFT.C2 and BoFT.C6) and three SOC1 homologs (BoSOC1.1.C4, BoSOC1.2.C4, and BoSOC1.C3) were functioning for the regulation of floral transition in B. oleracea. In addition, by phylogenic and syntenic analyses, a total of five FLC homologs, named BoFLC1.a, BoFLC1.b, BoFLC2, BoFLC3, and BoFLC5, were identified in the genome of B. oleracea. Transcriptomic analysis indicated that these genes could be grouped into vernalization-responsive (BoFLC2 and BoFLC3) and vernalization-insensitive genes (BoFLC1.a, BoFLC1.b, and BoFLC5). As green plant vernalization type, it might suggest the existence of vernalization-insensitive BoFLC homologs in young seedlings might be the reason why cabbage exhibits longer exposure of cold compared to seed vernalization type plants such as Chinese cabbage and Arabidopsis. These findings improve our understanding of the molecular dynamics underlying floral transition in cabbage plants.