Perturbation of periodic spot-generation balance leads to diversified pigmentation patterning of harlequin Phalaenopsis orchids: in silico prediction

Abstract Harlequin Phalaenopsis orchids are known for unprecedented clownish dark reddish-purple patches. The unreproducible diversified pigmentation patterning of harlequin flowers is an obstacle to commercialization. Insertion of a retrotransposon HORT1 in the promoter of a transcription activator for spotted pigmentation, PeMYB11, explains the patterning diversity. Nonetheless, in the absence of solo-LTR of HORT1, a transcriptional enhancer of PeMYB11, purple patches can still be generated in the presence of full-length HORT1, a transcriptional silencer of PeMYB11. Intriguingly, PeMYBx, a repressor for anthocyanin accumulation, is highly enriched in the purple region. Meanwhile, miR858 significantly expresses in the white region of harlequin flowers. To fill the knowledge gap, we refined the biological model for generating anthocyanin spots in Phalaenopsis, and then mathematically modeled the interactions with additional considerations of full-length HORT1 and the solo-LTR of HORT1, and altered amount of miR858. Our simulation suggests that not only the solo-LTR of HORT1 but also the reduced amount of miR858 take charge of the generation of purple patches but in an antagonistic manner. Our work extends the current understanding of how HORT1 and miR858 are involved in regulating the pigmentation patterning of harlequin Phalaenopsis and provides an experimental framework for future research.