Linker histones (H1) are structural elements of chromatin that influence its organization and function. In Arabidopsis, three H1 variants were identified and shown to be important for regulation of developmental processes and stress responses (Rutowicz et al., 2015; 2019). Studies in animals indicate existence of the crosstalk between H1s and other chromatin regulatory elements including Polycomb PRC complexes and HETEROCHROMATIN PROTEIN1 (HP1) (Nielsen et al., 2001; Teano et al., 2023). In Arabidopsis, a link between DNA methylation and PRC-dependent H3K27 methylation has been documented (Zemach et al., 2013; Teano et al., 2023).
Interestingly, plant PRC2 complex contains LHP1, a protein which shares significant structure similarity to animal HP1 (Libaut et al., 2005). Therefore, we have investigated possible functional link between H1 histones and LHP1 , by taking advantage of a relatively low number of H1 variants and viability of H1-depleted mutant line in Arabidopsis. Mutant lines carrying different combinations of mutations in H1 variants and LHP1 genes were generated, followed by phenotypic and molecular analyses. Triple H1 mutation (3h1) strongly enhanced the phenotype of lhp1, indicating genetic interaction between H1 and LHP1. Moreover, we found physical interaction between all H1 variants and LHP1. To characterise H1-LHP1 relationship in regulation of gene expression, we performed RNA-seq and K27me3 ChiP experiments using lhp1, 3h1, and lhp1/3h1 mutants. Our results support functional connection between linker histones and LHP1 and suggest that H1s can perform regulatory functions through collaborations with other chromatin factors.
This work was supported by National Science Centre grant 2021/41/N/NZ2/04423.