Early flowering in oilseed-type Brassica rapa plants results from nonsense-mediated mRNA decay (NMD) of BrFLC2

Abstract

Many Brassica species require vernalization (long-term winter-like cooling) for transition to the reproductive stage. In the past several decades, scientific efforts have been made to discern the molecular mechanisms underlying vernalization in many species. Thus, to identify the key regulators required for vernalization in Brassica rapa L., we constructed a linkage map composed of 7,833 single nucleotide polymorphism (SNP) markers using the late-flowering Chinese cabbage (B. rapa L. ssp. pekinensis) inbred line Chiifu and the early-flowering yellow sarson (B. rapa L. ssp. trilocularis (Roxb.)) line LP08 and identified a single major QTL on the upper-arm of the chromosome A02. In addition, we compared the transcriptomes of the lines Chiifu and LP08 at five vernalization time points, including both non-vernalized and post-vernalization conditions. We observed that BrFLC2 was significantly downregulated in the early flowering LP08 and had two deletion sites around the BrFLC2 genomic region compared with the BrFLC2 genomic region in Chiifu. In the present study, we also demonstrate that early flowering in LP08 line is attributed to the low expression of BrFLC2, which is caused by nonsense-mediated mRNA decay (NMD). Therefore, this study provides a better understanding of the molecular mechanisms underlying floral transition in B. rapa. One sentence summaryNMD-mediated degradation of BrFLC2 mRNA transcripts is the main cause of rapid flowering of oilseed-type B. rapa LP08 plants.