Investigating the functions of Polycomb Group proteins in potato development

Abstract

Phenotypic plasticity enables plants to cope with ever-changing environmental conditions. This often involves regulated gene expression mediated by chromatin modifiers, such as Polycomb (PcG) and Trithorax (TrxG) group proteins. Previous studies in Arabidopsis have shown the involvement of PcG proteins in controlling the several developmental transitions in plants, however, their role in other important crops is still unexplored. S. tuberosum ssp. andigena is a photoperiod sensitive cultivar of potato, in which stolon-to-tuber development is under the strict control of short-day (SD) photoperiodic conditions. Previous studies have identified several transcription factors, mobile RNAs and plant growth hormones involved in controlling stolon to tuber development. Interestingly many of these factors also control floral transition in Arabidopsis.

In this study, we aimed to understand the role of selective PcG members StMSI1,StE(z)2 and StBMI1 in controlling tuber development under different photoperiodic conditions. Our investigation revealed differential expression of these genes in stolon under short day versus long day photoperiod condition. We further show that overexpression of PRC members StMSI1, StE(z)2 or knockdown of StBMI1 resulted in pleiotropic effects, including altered leaf architecture and reduced below-ground tuber yield. Interestingly, these lines exhibited enhanced miRNA156 accumulation accompanied by aerial tubers from axillary-nodes, similar to miRNA156-OE lines. Through RNA-sequencing analysis, we found that these lines had decreased expression of auxin and brassinosteroid signaling/transport genes, whereas increased expression of cytokinin related genes, possibly leading to reduced apical dominance and axillary stolon development. Using ChIP sequencing, we have identified the genes targeted by a PRC group histone methyltransferase StE(z)2 during tuber development. In addition to this we also investigated the genome-wide occupancy of two important histone modification H3K27me3 and H3K4me3 from SD induced stolon tissues. This has led us to identify the important genes involved in tuberization pathway that are epigenetically regulated. In summary, we show that PcG proteins play an important role in potato development in a photoperiod responsive pathway.