Temporal Expression Pattern of Bolting-Related Genes During Vernalization in Sugar Beet

To screen candidate marker genes implicated in vernalization, bolting-related agronomic traits and the expression of genes homologous to the bolting and flowering-related genes in Arabidopsis thaliana were investigated in KWS9147 during 16-week (w) chilling. Bolting-related agronomic traits showed that less than 10-w chilling was not sufficient for bolting. A transitional period was determined between 10 and 14 weeks when vernalization time was enough for bolting in some seedlings. After 14-w chilling, nearly all seedlings were well vernalized. At the transcriptional level, the expression of 19 candidate genes was significantly changed in response to chilling (change fold > 2 and P value < 0.05). In particular, three genes (BvGI, BvBTC1 and BvFVE1) were notable, as their expression continuously increased or decreased during 8–16-w chilling, when BI and BD were significantly changed. On the basis of correlation analysis, a co-expression network containing two modules was constructed. BvGI, BvBTC1 and BvFVE1 were located at the centre of the first module, which co-expressed with the other 3 photoperiodic genes. In the second module, BvFT1 and BvFT2 were associated with BvLHY, BvGATA22 and BvFVE2. Our study on the temporal expression pattern of bolting and flowering-related genes during vernalization provides valuable information for preliminary screening of key regulators and may facilitate the future molecular breeding of vernalization-insensitive varieties.