The AT-hook motif nuclear localized (AHL) gene family encodes transcription factors pivotal in regulating plant growth, development, and responses to abiotic stimuli, including low temperature, salinity, darkness, and drought. In this study, we systematically identified 21 BpAHL genes in birch and characterized their sequence features, evolutionary relationships, and expression dynamics. Phylogenetic analysis classified BpAHLs into two clades (Clade-A and Clade-B) and three types (Type-I, -II, and -III), based on PPC domain and AT-hook motifs. Chromosomal mapping revealed an even distribution across nine chromosomes and one contig, with dispersed duplication events recognized as the major driver of BpAHL family expansion. Tissue-specific expression profiling uncovered striking divergence: Type-I BpAHLs displayed root-predominant expression, whereas Type-II/III BpAHLs were highly expressed in plant flowers and leaves. Notably, Type-II/III BpAHL genes in leaves showed distinct expression patterns in response to cold and heat stresses, while Type-I BpAHLs in roots were down-regulated under salt stress. This study provides a comprehensive phylogenomic and functional analysis of the AHLs in birch, providing insights into their roles in enhancing abiotic stress resilience in forest trees.

Chromatin remodeling factors efficiently and precisely establish, maintain, regulate, and distinguish between chromatin states in eukaryotes. DECREASE in DNA METHYLATION 1 (DDM1) is an important heterochromatin remodeling factor in plants that is responsible for maintaining heterochromatin DNA methylation and suppressing most transposable elements. Previous studies have predominantly focused on the effects of DDM1 on chromatin, with only a few focusing on its remodeling mechanisms. However, recent studies have greatly advanced understanding of the remodeling functions of DDM1 and, in particular, have clarified the mechanisms involved. In this review, we discuss the newly identified remodeling functions and mechanisms of DDM1. As DDM1 is closely involved in histone variant exchange, we first introduce the main histone variants associated with chromatin states in plants. Next, we focus on how DDM1 promotes the deposition of specific histone variants and describe its other remodeling functions. We propose that the core function of DDM1 is the regulation of histone variant distribution. DDM1 maintains heterochromatin by regulating the deposition of H2A and H3 variants, particularly by facilitating the exchange of specific histone variants.