Jasmonic acid biosynthetic genes TgLOX4 and TgLOX5 are involved in daughter bulb development in tulip (Tulipa gesneriana).

The tulip bulbs are modified underground stems which originate from axillary meristems of mother bulb scales. Hormones including jasmonic acids (JAs) play key roles in regulating tulip bulb development. Here, we compared variations of daughter bulb development through transcriptomic profiling analysis and characterized the functions of JA biosynthesis related genes during daughter bulb enlargement. The results showed that tulip varieties exhibited contrasting bulb size variations. Transcriptomic analyses revealed that genes involved in plant hormones and development were significantly changed following tulip bulb growth, including two lipoxygenase genes TgLOX4 and TgLOX5. Ectopic overexpression of TgLOX4 and TgLOX5 in Arabidopsis enhanced endogenous JA content, improved plant growth and increased lateral root numbers. Silencing of these two genes in tulip repressed the growth of daughter bulbs. Furthermore, exogenous JA treatment promoted tulip bulb growth, whereas JA biosynthesis inhibitor sodium diethyldithiocarbamate (DIECA) inhibited this process. This study offers supporting evidence for the involvement of tulip TgLOX4 and TgLOX5 in the regulation of daughter bulb growth and development.