Ectopic Gene Expression and Organogenesis in Arabidopsis Mutants Missing BRU1 Required for Genome Maintenance

Chromatin reconstitution after DNA replication and repair is essential for the inheritance of epigenetic information, but mechanisms underlying such a process are still poorly understood. Previously, we proposed that Arabidopsis BRU1 functions to ensure the chromatin reconstitution. Loss-of-function mutants of BRU1 are hypersensitive to genotoxic stresses and cause release of transcriptional gene silencing of heterochromatic genes. In this study, we show that BRU1 also plays roles in gene regulation in euchromatic regions. bru1 mutations caused sporadic ectopic expression of genes, including those that encode master regulators of developmental programs such as stem cell maintenance and embryogenesis. bru1 mutants exhibited adventitious organogenesis, probably due to the misexpression of such developmental regulators. The key regulatory genes misregulated in bru1 alleles were often targets of PcG SET-domain proteins, although the overlap between the bru1-misregulated and PcG SET-domain-regulated genes was limited at a genome-wide level. Surprisingly, a considerable fraction of the genes activated in bru1 were located in several subchromosomal regions ranging from 174 to 944 kb in size. Our results suggest that BRU1 has a function related to the stability of subchromosomal gene regulation in the euchromatic regions, in addition to the maintenance of chromatin states coupled with heritable epigenetic marks.