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Plant Cell. 2019 Jul 2. pii: tpc.00367.2019. doi: 10.1105/tpc.19.00367. [Epub ahead of print]

Meiotic DNA Repair in the Nucleolus Employs a Non-homologous End Joining Mechanism.

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University of Vienna, Max F. Perutz Laboratories CITY: Vienna Austria [AT].
The University of North Carolina at Chapel Hill CITY: Chapel Hill STATE: North Carolina POSTAL_CODE: 27599-3280 United States Of America [US].
Max Perutz Labs Vienna, University of Vienna, Vienna Biocenter (VBC) CITY: Vienna Austria [AT]


Ribosomal RNA genes are arranged in large arrays with hundreds of rDNA units in tandem. These highly repetitive DNA elements pose a risk to genome stability since they can undergo non-allelic exchanges. During meiosis DNA double strand breaks (DSBs) are induced as part of the regular program to generate gametes. Meiotic DSBs initiate homologous recombination (HR) which subsequently ensures genetic exchange and chromosome disjunction. In Arabidopsis thaliana we demonstrate that all 45S rDNA arrays become transcriptionally active and are recruited into the nucleolus early in meiosis. This shields the rDNA from acquiring canonical meiotic chromatin modifications and meiotic cohesin and allows only very limited meiosis-specific DSB formation. DNA lesions within the rDNA arrays are repaired in a RAD51-independent, but LIG4-dependent manner, establishing that it is non-homologous end joining (NHEJ) that maintains rDNA integrity during meiosis. Utilizing ectopically integrated rDNA repeats we validate our findings and demonstrate that the rDNA constitutes a HR-refractory genome environment.

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