Characterization of MERISTEM DEFECTIVE as a splicing factor involved in the DNA damage response in plants

Abstract

Plants have developed an elaborate DNA damage response (DDR) to cope with the exogenous environmental agents and endogenous metabolic processes that can threaten the genome integrity by inducing DNA lesions. Recent evidence suggests that, as it is already well known in animal cells, RNA binding proteins (RBPs) might also have a role in the plant DDR. The focus of this research is the SPLICEOSOME ASSOCIATED FACTOR 1 (SART1)-related splicing factor MERISTEM DEFECTIVE (MDF). MDF has been described to be involved in meristem patterning and auxin regulation. Interestingly, MDF was also shown to be phosphorylated by ATAXIATELANGIECTASIA MUTADED (ATM) and/or ATM AND RAD3-RE-LATED (ATR) – two key regulators of the plant DDR- in response to genotoxic stress. Phenotypical analyses of MDF loss of function mutants revealed strong defects in genome stability such as reduced cell division, short root phenotype or accumulation of dead cells in the root apical meristem (RAM). Moreover, RNA-sequencing analyses uncovered that mdf-1 mutants display numerous transcription and splicing changes in genes associated to stress responses, development, cell division and metabolism. The finding that mdf mutants responded to short- and long-term treatments with DNA damaging agents differently than WT plants, further supported the role of MDF in coordinating stress responses (e.g., DNA damage) with cell division. Additionally, preliminary assays with phosphomutant variants suggested that the phosphorylation status of MDF influenced its activity. Altogether this study proofed that MDF is localized in the spliceosome and is important for pre-mRNA splicing, cell division control and Arabidopsis development. It also provides evidence of a conserved role for splicing factors in genome stability.