Banana MaSPL16 Modulates Carotenoid Biosynthesis during Fruit Ripening through Activating the Transcription of Lycopene β-Cyclase Genes.

Carotenoids are a class of bioactive compounds that exhibit health-promoting properties for humans, but their regulation in bananas during fruit ripening remains largely unclear. Here, we found that the total carotenoid content continued to be elevated along the course of banana ripening and peaked at the ripening stage followed by a decrease, which is presumably caused by the transcript abundances of carotenoid biosynthetic genes 1.1 and 1.2. Moreover, a ripening-inducible transcription factor MaSPL16 was characterized, which was a nuclear protein with transactivation activity. Transient transformation of 16 in banana fruits led to enhanced transcript levels of 1.1 and 1.2 and hence the total carotenoid accumulation. Importantly, MaSPL16 stimulated the transcription of 1.1 and 1.2 through directly binding to their promoters. Collectively, our findings indicate that MaSPL16 behaves as an activator to modulate banana carotenoid biosynthesis, which may provide a new target for molecular improvement of the nutritional and bioactive qualities of agricultural crops that accumulate carotenoids.