Genome-wide profiling of γH2AX in Arabidopsis

The R-loop, composed of a DNA-RNA hybrid and the displaced single-stranded DNA, regulates diverse cellular processes. However, how cellular R-loops are sensed remain poorly understood. Here we report the discovery of the evolutionally conserved ALBA proteins (AtALBA1&2) functioning as the R-loops sensor of genic regions in higher plant Arabidopsis thaliana. AtALBA1 and 2 form a heterodimer protein complex and localize in the nucleus. While AtALBA1 binds to the DNA-RNA hybrid strand, AtALBA2 associates with single-stranded DNA in the R-loops. AtALBA1&2 preferentially binds to the genic R-loop regions that are associated with active epigenetic marks. Depletion of AtALBA1 or AtALBA2 results in hypersensitivity of plants to DNA damaging agents. Our results demonstrate the unprotected R-loops by loss of AtALBA1&2 are main source of DNA damage through γH2AX ChIP-seq. We conducted γH2AX ChIP-seq with Arabidopsis wild-type (Col-0) and double mutant (alba1-1/alba2-1) seedlings to proflie the DNA damage .