Tissue- and expression level-specific chromatin looping at maize b1 epialleles

Abstract

This work examines the involvement of chromatin looping in the transcriptional regulation of two epialleles of the maize (Zea mays) b1 gene, B-l and B'. These two epialleles are tissue-specifically regulated and are involved in paramutation. B-l and B' are expressed at high and low levels, respectively. A hepta-repeat ∼100 kb upstream of the transcription start site (TSS) is required for both paramutation and high b1 expression. Using chromosome conformation capture, we show that the heptarepeat physically interacts with the TSS region in a tissue and expression level-specific manner. Multiple repeats are required to stabilize this interaction. High b1 expression is mediated by a multiloop structure; besides the hepta-repeat, other sequence regions physically interact with the TSS as well, and these interactions are epiallele-and expression level- specific. Formaldehyde-assisted isolation of regulatory elements uncovered multiple interacting regions as potentially regulatory. © 2009 American Society of Plant Biologists.