Comprehensive analysis of Arabidopsis thaliana DNA polymerase epsilon catalytic subunit A and B mutants - an insight into differentially expressed genes and protein-protein interactions

One of the main replicative enzymes in most eukaryotes, DNA polymerase {varepsilon} (POLE), is composed of four subunits, namely a single catalytic and three regulatory subunits. In Arabidopsis, the catalytic subunit of POLE is encoded by two genes: Arabidopsis thaliana DNA POLYMERASE EPSILON CATALYTIC SUBUNIT A (AtPOL2A) and B (AtPOL2B). Although studies have shown AtPOL2A to be involved in various biological processes, the role of AtPOL2B is unclear. Here, we investigated the transcriptomes of both atpol2a and atpol2b mutants, and the promoter sequences to provide a better insight into the targets of AtPOL2s at the molecular level. In the present study, leaf cDNA libraries of four AtPOL2 mutants (atpol2a-1 and atpol2b-1, -2 and - 3) were sequenced using the Illumina platform. Analysis of gene expression profiles identified a total of 198, 76, 141 and 67 differentially expressed genes in atpol2a-1, atpol2b-1, atpol2b-2 and atpol2b-3, respectively; the majority of pericentromeric transposable elements were transcriptionally active in atpol2a-1 as compared to atpol2b mutants and wild type. Protein-protein interaction network analysis and molecular docking identified three (CER1, RPA1E and AT5G60250) and two (PR1 and AT5G48490) proteins as potential interactors (cluster size > 60 and balanced score < -900) of AtPOL2A and AtPOL2B, respectively; Interestingly, these five proteins also showed a significant interaction between POLE catalytic subunit of Saccharomyces cerevisiae. Our in silico promoter analysis showed that the AtPOL2A promoter sequence is overrepresented with cis-acting regulatory elements (CREs) associate with cell cycle regulation, meristematic/reproductive tissue-specific pattern of expression and MYB protein recognition, whereas the AtPOL2B promoter sequence was mainly enriched with stress-responsive elements. The information provided here has led to the identification of targets of AtPOL2s at the molecular level and CREs putatively associated with the regulation of AtPOL2s. To our knowledge, this study provides the first comparative transcriptome profiling of single-gene mutants of AtPOL2s.