The R2R3-MYB transcription factor LcMYBC2-L1 represses anthocyanin biosynthesis in Litchi chinensis Sonn.

Abstract

MYB transcription factors are key regulators of anthocyanin biosynthesis, acting as both activators and repressors. However, the functional characterization of R2R3-MYB repressors in litchi (Litchi chinensis) remains limited. In this study, we identified and characterized LcMYBC2-L1 as an R2R3-MYB transcriptional repressor that negatively regulates anthocyanin accumulation. LcMYBC2-L1 contained conserved basic helix-loop-helix (bHLH)-binding, C1 (LIsrGIDPxT/SHRxI/L), and C2 (pdLNLD/ELxiG/S) motifs, localizes to the nucleus, and exhibits transcriptional repression activity. Overexpression of LcMYBC2-L1 in tobacco suppressed anthocyanin biosynthesis, resulting in white petals. Heterologous expression of LcMYBC2-L1 in tobacco (Nicotiana tabacum) suppressed anthocyanin biosynthesis and resulted in the production of white petals. Importantly, overexpression of LcMYBC2-L1 and its mutation variants in red litchi calli overexpressing LcMYB1 led to significantly reduced anthocyanin accumulation and downregulation of biosynthetic genes, confirming the repressive role of LcMYBC2-L1 in anthocyanin biosynthesis. The C2 motif was shown to be essential for the inhibitory function of LcMYBC2-L1. Protein interaction assays revealed that LcMYBC2-L1 could interact with both LcMYB1 and LcbHLH1/3, thereby interfering with the formation of the activated LcMYB1–LcbHLH3 complex and suppressing the expression of downstream anthocyanin biosynthetic genes. Taken together, our findings establish that LcMYBC2-L1 represses anthocyanin biosynthesis by disrupting the LcMYB1–LcbHLH3 complex via its C2 repression motif, providing new insights into the R2R3-MYB-mediated regulatory mechanisms of anthocyanin production in plants.

Keywords

Litchi chinensis Sonn. / Anthocyanin / Transcriptional repressor / R2R3-MYB / LcMYBC2-L1 / LcMYB1–LcbHLH3 complex

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Funding

the National Key Research and Development Program(2024YFD1600301)

the National Natural Science Foundation of China(32272663)

the Science and Technology Planning Project of Guangzhou(2023B01J2002)

China Litchi and Longan Industry Technology Research System(CARS-32-05)

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