Papaya regulate carotenoid biosynthesis-related genes during papaya fruit ripening.

The ripening of papaya is a physiological and metabolic process associated with accumulation of carotenoids, alternation of flesh color and flavor, which depending on genotype and external factors such as light and hormone. Transcription factors regulating carotenoid biosynthesis have not been analyzed during papaya fruit ripening. RNA-Seq experiments were implemented using different ripening stages of papaya fruit from two papaya varieties. -elements in lycopene β-cyclase genes ( and ) were identified, and followed by genome-wide analysis to identify transcription factors binding to these -elements, resulting in the identification of and , two bHLH genes. The expressions of were changed during fruit development, coupled with transcript increase of carotenoid biosynthesis-related genes including , , , , , and . Yeast one-hybrid (Y1H) and transient expression assay revealed that could bind to the promoters of and , and regulate their transcriptions. In response to strong light, the results of elevated expression of carotenoid biosynthesis-related genes and the changed expression of indicated that were involved in light-mediated mechanisms of regulating critical genes in the carotenoid biosynthesis pathway. Collectively, our findings demonstrated several TF family members participating in the regulation of carotenoid genes and proved that and individually regulated the transcription of lycopene β-cyclase genes ( and ). This study yielded novel findings on regulatory mechanism of carotenoid biosynthesis during papaya fruit ripening.