Analyses of gene copy number variation in diverse epigenetic regulatory gene families across plants: Increased copy numbers of BRUSHY1/TONSOKU/MGOUN3 (BRU1/TSK/MGO3) and SILENCING DEFECTIVE 3 (SDE3) in long-lived trees

Long-lived trees experience high risk of damage due to the various types of stresses over their lifespans. Epigenetic regulation is involved in gene regulation, genome integrity, and inhibition of exogenous genetic elements, which are functions important for long-term survival. To narrow down the candidate genes related to tree longevity among diverse epigenetic regulatory genes, it is necessary to identify epigenetic regulatory genes with increased copy number in long-lived tree species as compared to in short-lived annual and perennial herb species. In the present study, to find out the epigenetic regulatory genes with increased copy number in tree species as compared to in annual and perennial herb species, we conducted the systematic comparison of copy number variation in 121 gene families involved in various epigenetic regulatory pathways across 85 plant species with different lifespans using a genome database. Among these 121 gene families, the gene family encoding BRUSHY1/TONSOKU/MGOUN3 (BRU1/TSK/MGO3) and that encoding SILENCING DEFECTIVE 3 (SDE3) were found to exhibit significantly higher copy number of genes in tree species than in both perennial and annual herb species. BRU1/TSK/MGO3 is involved in chromatin modifications and plays an important role in the maintenance of meristems, genome integrity, and the inheritance of chromatin states. SDE3 is involved in RNA silencing and has an important role in antiviral defense through posttranscriptional gene silencing. The systematic comparison of copy number variation in diverse epigenetic regulatory gene families among plant species can find out epigenetic regulatory genes with increased copy number in long-lived tree species and enhance subsequent studies for understanding the relationship between epigenetic regulation and tree longevity.