AcMYB12 and AcMYB29 promote flavonol biosynthesis through transcriptional regulation in onion (Allium cepa L.)

Flavonols possess significant medical value and are essential for plant stress resistance. These compounds constitute primary components of the nutritional value in onions, particularly in edible portions. While the flavonol biosynthetic pathway has been extensively studied, its regulatory mechanisms in onions remain incompletely understood. This investigation identified flavonol biosynthesis and regulatory genes through analysis of transcriptome and metabolomics data from different developmental stages of ‘SA1’. Two R2R3-MYB transcription factors, AcMYB12 and AcMYB29, were identified as positive regulators of onion flavonol biosynthesis. Transcriptional activation assays demonstrated that both could activate AcCHS, AcF3xH, and AcFLS. Yeast one-hybrid assays confirmed their direct binding to these gene promoters. The expression levels of flavonol pathway genes and flavonol contents in AcMYB12/AcMYB29-overexpressing onion calli and Arabidopsis plants were significantly higher than those in the control group. Transient silencing assays revealed partial functional redundancy between these two transcription factors. Notably, their regulatory capabilities exhibited significant differences. AcMYB12 predominantly regulates flavonol accumulation, while AcMYB29 specifically influences quercetin. Further investigation of the molecular mechanisms underlying differential regulation indicated variations in cis-elements within flavonol pathway gene promoters and differences in binding activity between transcription factors and cis-elements.