Physiological and Molecular Characterization of Two Radish Inbred Lines Showing Different Bolting Time

The radish (Raphanus sativus L.) is an important Brassicaceae root vegetable crop. The main edible part is its taproot which contains sources of carbohydrates, dietary fiber, organic nutrients, and valuable phytochemicals to human beings. Our study is major challenges to prevent premature bolting in spring plantings. We performed characterization of two different bolting time inbred lines, “Late bolting radish" (NH-JS1) and “Early bolting radish" (NH-JS2) generated by a breeding approach. These lines showed different flowering phenotypes depending on vernalization time at 4°C. Under the vernalization for 15 days, NH-JS2 plants were completely flowering from 40 days after vernalization, whereas only 5% of NH-JS1 plants were flowering at the same condition. We measured gene expression of major flowering time-related genes between two lines by qRT-PCR analysis. The RsFLC1, plays a central role in the timing of initiation of flowering as a strong repressor, highly expressed in the NH-JS1 compared to NH-JS2 at the both no and vernalization treatment conditions. The RsFRI, a positive regulator of FLC, also highly expressed in the NH-JS1 regardless of vernalization treatment. In contrast, the RsSOC1, suppressed by FLC, showed the most difference between two lines in the vernalization conditions which is maximum over 5-fold higher in NH-JS2 than NH-JS1. These results suggest that the correlations between gene expression and flowering time in response to the vernalizations in controlled-environment experiments using two inbred lines with different bolting time, indicating that the transcript expression levels of flowering genes has the potential to understand radish flowering pathway or mechanism.