Nespor Dadejova, M. | Search bioRxiv

bioRxiv2021

Loss of FAS1 function reveals rescue of an aberrant intra-S-phase checkpoint by the G2/M checkpoint regulator SOG1

The WEE1 and ATR kinases represent important regulators of the plant intra-S-phase checkpoint, as evidenced by the hypersensitivity of WEE1KO and ATRKO roots to replication inhibitory drugs. Here, we report on the identification of a defective allele of the FASCIATA1 (FAS1) subunit of the chromatin assembly factor 1 (CAF-1) complex as a suppressor of WEE1- or ATR-deficient plants. We demonstrate that lack of FAS1 activity results in the activation of an ATM- and SOG1-mediated G2/M-arrest that makes the ATR and WEE1 checkpoint regulators redundant. This ATM activation accounts for telomere erosion and loss of ribosomal DNA described for the fas1 plants. Knocking out SOG1 in the fas1 wee1 background restores replication stress sensitivity, demonstrating that SOG1 plays a prominent role as secondary checkpoint regulator in plants that fail to activate the intra-S-phase checkpoint. One-Sentence SummaryLack of the chromatin assembly factor-1 subunit FAS1 results in a DNA damage response that overrules the need for replication checkpoint activators.

plant biology↗

bioRxiv2020

Disruption of NAP1 genes supresses the fas1 mutant phenotype and enhances genome stability

Histone chaperones mediate assembly and disassembly of nucleosomes and participate in essentially all DNA-dependent cellular processes. In Arabidopsis thaliana, loss-of-functions of FAS1 or FAS2 subunits of the H3-H4 histone chaperone complex CHROMATIN ASSEMBLY FACTOR 1(CAF-1) has a dramatic effect on plant morphology, growth and overall fitness. Altered chromatin compaction, systematic loss of repetitive elements or increased DNA damage clearly demonstrate the severity of CAF-1 dysfunction. How histone chaperone molecular networks change without a functional CAF-1 remains elusive. Here we present an intriguing observation that disruption of the H2A-H2B histone chaperone NUCLEOSOME ASSEMBLY PROTEIN 1 (NAP1) supresses FAS1 loss-of function. The quadruple mutant fas1nap1;1-3 shows wild-type growth and decreased sensitivity to genotoxic stress. Chromatin of fas1nap1;1-3 plants is less accessible to micrococcal nuclease and progressive loss of telomeres and 45S rDNA is supressed. Interestingly, the strong genetic interaction between FAS1 and NAP1 does not occur via direct protein-protein interaction. We propose that NAP1;1-3 play an essential role in nucleosome assembly in fas1, thus their disruption abolishes fas1 defects. Our data altogether reveal a novel function of NAP1 proteins, unmasked by CAF-1 dysfunction. It emphasizes the importance of a balanced composition of chromatin and shed light on the histone chaperone molecular network.

molecular biology↗