PcG proteins MSI1 and BMI1 function upstream of miR156 to regulate aerial tuber formation in potato

In this project, we investigated the role of two Polycomb Repressive Complexe (PRC) proteins, StMSI1 (PRC2 member) and StBMI1-1, in potato development. In wild-type andigena plants, StMSI1 and miRNA156 levels increase in stolon, whereas StBMI1-1 reduces under short-day conditions. StMSI1-OE and StBMI1-1-antisense lines showed enhanced accumulation of miRNA156 accompanied with development of aerial stolons/tubers from axillary-nodes under short-day conditions. In order to investigate the basis for aerial stolon/tuber formation, RNA-sequencing was performed using axillary-nodes from StMSI1-OE and StBMI1-1-antisense lines along with vector control (VC) plants , which revealed downregulation of auxin, brassinosteroid and upregulation of cytokinine transport/signaling genes . Moreover, we observed downregulation of genes encoding PRC1 members and upregulation of Trithorax group H3K4-methyl-transferases in StMSI-OE line. ChIP-qPCR further confirmed H3K27me3-mediated suppression of StBMI1-1/3, and H3K4me3-mediated activation of miRNA156 in StMSI1-OE plants. Overall, we show that a crosstalk of histone-modifiers regulate miRNA156 and alters hormonal response during aerial tuber formation in potato under short-day conditions.