Heritable epigenetic modification of BpPIN1 is associated with leaf shapes in Betula pendula.

This article focuses on identifying the genetic and epigenetic basis of the lobed leaf shape in Betula pendula 'Dalecarlica', a birch variety selected for its ornamental lobed leaves. Using bulked segregant analysis sequencing (BSA-seq) and fine molecular mapping, the study localized the trait to a 92.4-kb region on chromosome 7 containing the gene BpPIN1, which encodes a PIN-FORMED1 auxin efflux carrier. Although no coding sequence mutations were linked to leaf shape, differential expression of BpPIN1 was associated with hypomethylation of CHH-context DNA methylation sites in its promoter region, particularly near an auxin response factor (ARF) cis-element, implicating RNA-directed DNA methylation (RdDM) in regulating BpPIN1 expression. The findings suggest that epigenetic modification of BpPIN1 influences auxin distribution during leaf development, leading to the lobed leaf phenotype, and provide insights relevant for molecular breeding of ornamental traits in birch.