A 215-bp indel at intron I of BoFLC2 affects flowering time in Brassica oleracea var. capitata during vernalization

Abstract

In response to cold, a 215-bp deletion at intron I of BoFLC2 slows its silencing activity by feedback to the core genes of the PHD-PRC2 complex, resulting in late flowering in cabbage. Cabbage is a plant-vernalization-responsive flowering type. In response to cold, BoFLC2 is an important transcription factor, which allows cabbage plants to remain in the vegetative phase. However, there have been few reports on the detailed and functional effects of genetic variation in BoFLC2 on flowering time in cabbage. Herein, BoFLC2^E and BoFLC2^L, cloned from extremely early and extremely late flowering cabbages, respectively, exhibited a 215-bp indel at intron I, three non-synonymous SNPs and a 3-bp indel at exon II. BoFLC2^L was found to be related to late flowering, as verified in 40 extremely early/late flowering accessions, a diverse set of cabbage inbred lines and two F2 generations by using indel-FLC2 marker. Among the genetic variation of BoFLC2, the 215-bp deletion at intron I was the main reason for the delayed flowering time, as verified in the transgenic progenies of seed-vernalization-responsive Arabidopsis thaliana (Col) and rapid cycler B. oleracea (TO1000, boflc2). This is the first report to show that the intron I indel of BoFLC2 affects the flowering time of cabbage. Although the intron I 215-bp indel between BoFLC2^E and BoFLC2^L did not cause alternative splicing, it slowed BoFLC2^L silencing during vernalization and feedback to the core genes of the PHD-PRC2 complex, resulting in their lower transcription levels. Our study not only provides an effective molecular marker-assisted selective strategy for identifying bolting-resistant resources and breeding improved varieties in cabbage, but also provides an entry point for exploring the mechanisms of flowering time in plant-vernalization-responsive plants.