Expression analysis of bulb development-related genes in onion cultivars

Onion (Allium cepa L.) is one of the most widely produced and consumed vegetable crops worldwide. The bulb size of onion is an important factor in its productivity. It is known that bulb development is induced and continues under long day length and is inhibited under short day length. These responses have also been characterized at the genetic level, with studies indicating that expression of AcFT1, which encodes an FT-like protein for bulb development, is upregulated under long day length and downregulated under short day length. Conversely, a further AcFT gene, AcFT4, which promotes leaf initiation and suppresses bulb development, is upregulated under short day length, and downregulated under long day length. In this study, we conducted expression analysis of AcFT1 and AcFT4 using individual leaves of the cultivar 'Momiji No. 3' to evaluate the difference in day length response. Our expression analysis from 0 weeks after transplanting (WAT) to 8 WAT indicated that the expression of AcFT1 and AcFT4 in the preceding leaf was higher than that in newly initiated leaves from 4 to 8 WAT. These results indicate that the preceding leaves play an important role in the response of onions to day length for leaf initiation or bulb development. We also conducted an RNA-seq analysis to identify candidate genes for bulb development.