Systematic analysis of MYB transcription factors in lotus (Nelumbo nucifera) reveals NnMYB48 as a positive regulator of aporphine alkaloid biosynthesis.

Abstract

Aporphine alkaloids in lotus (Nelumbo nucifera) are medicinally significant compounds, and their biosynthesis is orchestrated by a complex network involving various transcription factors (TFs). MYB TFs constitute one of the most critical classes, yet their specific functions in lotus aporphine alkaloid biosynthesis remained largely unexplored. Using the newly assembled lotus telomere-to-telomere (T2T) genome, we systematically characterized the full complement lotus MYB genes and identified 126 R2R3-MYBs, 57 1R-MYBs, five R1R2R3-MYBs, and one 4R-MYB. Phylogenetic and gene duplication analysis revealed 63 collinear NnMYB gene pairs and 15 tandemly arrayed gene clusters, indicating that both whole-genome and local tandem duplication events collectively drove the expansion of the NnMYB family. Correlation analysis between gene expression and aporphine abundance identified 44 NnMYB candidates potentially involved in aporphine biosynthesis. Among them, NnMYB48 was predominantly expressed in the lotus leaves and showed a rapid transcriptional response to methyl jasmonate (MeJA). Transient overexpression of NnMYB48 in lotus petals markedly upregulated multiple aporphine biosynthetic genes and increased the accumulation of major aporphine alkaloids. Further dual-luciferase reporter assays, yeast one-hybrid, and electrophoretic mobility shift assays confirmed that NnMYB48 directly binds to the promoters of NnTYDC and NnCYP80G, thereby activating their transcription and promoting alkaloid biosynthesis. Collectively, these findings provide critical insights into the evolution trajectory and functional diversification of the NnMYB family in lotus.

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