Histone chaperones mediate the assembly and disassembly of
nucleosomes and participate in essentially all
DNA-dependent cellular processes. In Arabidopsis thaliana, loss-of-function 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. CAF-1 dysfunction can lead to altered
chromatin compaction, systematic loss of repetitive elements or increased DNA damage, clearly demonstrating its severity. How
chromatin composition is maintained without functional CAF-1 remains elusive. Here we show that disruption of the H2A-H2B
histone chaperone NUCLEOSOME ASSEMBLY PROTEIN 1 (
NAP1) suppresses the FAS1 loss-of-function phenotype. The quadruple mutant fas1
nap1;1
nap1;2
nap1;3 shows wild-type growth, decreased sensitivity to genotoxic stress and suppression of telomere and 45S
rDNA loss.
Chromatin of fas1
nap1;1
nap1;2
nap1;3 plants is less accessible to
micrococcal nuclease and the nuclear H3.1 and H3.3
histone pools change compared to fas1. Consistently, association between
NAP1 and H3 occurs in the cytoplasm and nucleus in vivo in protoplasts. Altogether we show that
NAP1 proteins play an essential role in DNA repair in fas1, which is coupled to
nucleosome assembly through modulation of H3 levels in the nucleus.