Light promotes pharmacological activities of bitter gourd (Momordica charantia) via McHY5/McHY5-X1 and McPIF1-X1/McPIF3 antagonistic regulation in MAP30 transcription

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• Light promotes the transcription level of MAP30 . • McHY5 and McHY5-X1 activate MAP30 expression mainly under light conditions. • McPIF1-X1 and McPIF3 are negative regulators for MAP30 transcription. • McHY5/McHY5-X1 and McPIF1-X1/McPIF3 antagonistically regulate MAP30 expression. MAP30, a ribosome-inactivating protein mainly isolated from the fruits and seeds of bitter gourd ( Momordica charantia ), has many pharmacological properties, such as anti-HIV and anti-tumor activities. Using qPCR analysis, we found that MAP30 transcription was higher in light, but drastically reduced in darkness. However, the molecular mechanism by which MAP30 is regulated remains unclear. Using yeast one-hybrid (Y1H) library screening, we found that McHY5, a homolog of AtHY5, bound to the MAP30 promoter. In addition, McHY5 and its homolog McHY5-X1 are identified as positive regulators binding to the MAP30 promoter by using Y1H, Electrophoretic mobility shift assay (EMSA) and Dual-Luciferase Reporter (DLR) assay. Due to MAP30 is not present in Arabidopsis we transformed pMAP30:MAP30 to Col and obtained transgenic line 18. Compared with pMAP30:MAP30/Col 18#, MAP30 transcription was largely reduced in pMAP30:MAP30 18#/Athy5–215 whether under light or dark conditions. Moreover, approximately 70 % of the tested bitter gourd germplasms showed consistent expression patterns of McHY5 / McHY5-X1 and MAP30 under light conditions. In contrast to McHY5, McPIF1-X1 and McPIF3 acted as inactivators to inhibit MAP30 transcription. In this study, we found that MAP30 transcription was activated by McHY5 and McHY5-X1 in light, while McPIF1-X1 and McPIF3 inhibited MAP30 transcription mainly in darkness. Conclusively, we established the antagonistic module of McHY5/McHY5-X1 and McPIF1-X1/McPIF3 in MAP30 transcription regulation. This work expands our understanding of the regulatory mechanism of MAP30 and provides a valuable conceptual guidance for cultivating high pharmacological activity bitter gourd varieties with high MAP30 protein levels.

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