RdDM-Associated Chromatin Remodelers in Soybean: Evolution and Stress-Induced Expression of CLASSY Genes

RNA-directed DNA methylation (RdDM) is an epigenetic mechanism involved in several biological processes in plants, requiring complex machinery including the chromatin remodeling protein CLASSY (CLSY). The CLSY family regulates global and locus-specific DNA methylation and was initially identified in Arabidopsis thaliana. Despite reports in other plants, detailed knowledge about CLSY proteins in soybean is scarce. In this work, we used profile hidden Markov models (profile HMMs) specifically constructed for CLSY detection to identify new members in soybean and to analyze their phylogenetic relationships across bryophyte, basal angiosperm, basal eudicot, monocots, and eudicots. We identified two new candidates for CLSY1-2 and one for DRD1 in soybean and, for the first time, detected CLSY and DRD1 genes in Aquilegia coerulea. Phylogenetic analysis indicated two main CLSY groups: one similar to Arabidopsis CLSY1-2 and another to CLSY3-4. Gene duplication analysis demonstrated that whole-genome duplication/segmental duplication events contributed to CLSY family expansion in soybean. RT-qPCR analysis showed that CLSY and five other epigenetic regulator genes had stress-modulated expression during soybean germination under salt and osmotic stress, with variation among cultivars. Our findings enhance comprehension of the evolutionary dynamics of the CLSY family and furnish insights into their response to abiotic stress in soybean.