An Arabidopsis FANCJ helicase homologue is required for DNA crosslink repair and rDNA repeat stability

Abstract

Proteins of the Fanconi Anemia (FA) complementation group are required for crosslink (CL) repair in humans and their loss leads to severe pathological phenotypes. Here we characterize a homolog of the Fe-S cluster helicase FANCJ in the model plant Arabidopsis, AtFANCJB, and show that it is involved in interstrand CL repair. It acts at a presumably early step in concert with the nuclease FAN1 but independently of the nuclease AtMUS81, and is epistatic to both error-prone and error-free post-replicative repair in Arabidopsis. The simultaneous knock out of FANCJB and the Fe-S cluster helicase RTEL1 leads to induced cell death in root meristems, indicating an important role of the enzymes in replicative DNA repair. Surprisingly, we found that AtFANCJB is involved in safeguarding rDNA stability in plants. In the absence of AtRTEL1 and AtFANCJB, we detected a synergetic reduction to about one third of the original number of 45S rDNA copies. It is tempting to speculate that the detected rDNA instability might be due to deficiencies in G-quadruplex structure resolution and might thus contribute to pathological phenotypes of certain human genetic diseases.

G4 Structures in Control of Replication and Transcription of rRNA Genes

“…30% of their standard copy number ( Rohrig et al, 2016 ). A similar contribution to rDNA stability was also observed in another Fe-S cluster helicase – FANCJ homolog in Arabidopsis – AtFANCJB ( Dorn et al, 2019 ).…”

Meiotic DNA Repair in the Nucleolus Employs a Nonhomologous End-Joining Mechanism

“…Interestingly, LIG4 is also needed to maintain 45S rDNA during extended somatic growth. In this context, it is important to mention two recent studies that highlight the involvement of Fanconi Anemia Complementation group J (FANCJ) and Regulator of Telomere Helicase (RTEL) helicases in 45S rDNA maintenance, most likely by resolving complex replication intermediates (Röhrig et al, 2016;Dorn et al, 2019). Future studies are needed to clarify the epistatic relation of these factors with LIG4.…”

Epigenetic silencing of clustered tDNAs in Arabidopsis

“…Moreover, considering the high variability of rRNA gene copy numbers through cell divisions in human and in plant clusters 66 67 , it seems that these particular genomic arrangements are submitted to a high flexibility. Interestingly, Arabidopsis plants defective for the cross link repair factor RTEL1 exhibit significant reduction of 45S rDNA copies 68 highlighting that DNA repair factors also contribute to maintain repeats integrity. Addtionally, ddm1 Arabidopsis plants display higher somatic and meiotic recombination frequencies 69 suggesting that maintenance of both genome and methylome integrities are interconnected.…”