Abstract
Color is an important trait for horticultural crops. Carotenoids are one of the main pigments for coloration and have important implications for photosynthesis in plants and benefits for human health. Here, we identified an APETALA2 (AP2)/ETHYLENE RESPONSE FACTOR (ERF) transcription factor named MdAP2-34 in apple (Malus domestica Borkh.). MdAP2-34 expression exhibited a close correlation with carotenoid content in ‘Benin Shogun’ and ‘Yanfu 3’ fruit flesh. MdAP2-34 promotes carotenoid accumulation in MdAP2-34-OVX transgenic apple calli and fruits by participating in the carotenoid biosynthesis pathway. The major carotenoid contents of phytoene and β-carotene were much higher in overexpressing MdAP2-34 transgenic calli and fruit skin, yet the predominant compound of lutein showed no obvious difference, indicating that MdAP2-34 regulates phytoene and β-carotene accumulation but not lutein. MdPSY2-1 (phytoene synthase 2) is a major gene in the carotenoid biosynthesis pathway in apple fruit, and the MdPSY2-1 gene is directly bound and transcriptionally activated by MdAP2-34. In addition, overexpressing MdPSY2-1 in apple calli mainly increases phytoene and total carotenoid contents. Our findings will advance and extend our understanding of the complex molecular mechanisms of carotenoid biosynthesis in apple, and this research is valuable for accelerating the apple breeding process.
Highlights
Color is an important trait for horticultural crops, such as fruits, vegetables, and flowers[1]
Pearson’s correlation (r) between each AP2 transcription factors (TFs) transcript levels and total carotenoid content in apple flesh of ‘Benin Shogun’ and ‘Yanfu 3’ indicated that the expression level of MdAP2-34 was significantly positively associated with carotenoid contents (Supplemental Table S2)
The expression levels of genes related to carotenoid biosynthesis were measured and analyzed in transgenic apple calli (TAC) and transgenic Granny Smith fruit skin (TFS) using qRT–PCR (Fig. 3)
Summary
Color is an important trait for horticultural crops, such as fruits, vegetables, and flowers[1]. Previous studies indicated that MdPSY2 played a dominant role in carotenoid accumulation in apple fruits and was activated by AP2/ERF TFs15,41. Pearson’s correlation (r) between each AP2 TF transcript levels and total carotenoid content in apple flesh of ‘Benin Shogun’ and ‘Yanfu 3’ indicated that the expression level of MdAP2-34 was significantly positively associated with carotenoid contents (Supplemental Table S2).
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