Comprehensive Classification of the RNase H-like domain-containing Proteins in Plants

Background R-loop is a nucleic acid structure containing an RNA-DNA hybrid and a displaced single-stranded DNA. Recently, accumulated evidence showed that R-loops widely present in various organisms’ genomes and are involved in many physiological processes, including DNA replication, RNA transcription, and DNA repair. RNase H-like superfamily (RNHLS) domain-containing proteins, such as RNase H enzymes, are essential in restricting R-loop levels. However, little is known about the function and relationship of other RNHLS proteins on R-loop regulation, especially in plants. Results In this study, we characterized 6193 RNHLS proteins from 13 representative plant species and clustered these proteins into 27 clusters, among which reverse transcriptases and exonucleases are the two largest groups. Moreover, we found 691 RNHLS proteins in Arabidopsis with a conserved catalytic alpha-helix and beta-sheet motif. Interestingly, each of the Arabidopsis RNHLS proteins is composed of not only an RNHLS domain but also another different protein domain. Additionally, the RNHLS genes are highly expressed in different meristems and metabolic tissues, which indicate that the RNHLS proteins might play important roles in the development and maintenance of these tissues. Conclusions In summary, we systematically analyzed RNHL proteins in plants and found that there are mainly 27 subclusters of them. Most of these proteins might be implicated in DNA replication, RNA transcription, and nucleic acid degradation. We classified and characterized the RNHLS proteins in plants, which may afford new insights into the investigation of novel regulatory mechanisms and functions of R-loops.