XXXX homologues of the histone chaperone @entity40654 are crucial for chromatin replication and cell proliferation in plant development.

@entity958 @entity17748 @entity40654 @entity72278 @entity72279 @entity375 @entity40312 @entity40313
Anti-silencing function1 ( @entity40654 ) is an evolutionarily conserved histone chaperone. Studies in @entity375 and animals indicate that @entity40654 proteins play important roles in various chromatin-based processes, including gene transcription, DNA replication and repair. While two genes encoding @entity40654 homologues, @entity40312 and @entity40313 , are found in the @entity958 genome, their function has not been studied. Here we report that both @entity40312 and @entity40313 proteins bind histone H3, and are localized in the cytoplasm and the nucleus. Loss-of-function of either @entity40312 or @entity40313 did not show obvious defects, whereas simultaneous knockdown of both genes in the double mutant Atasf1ab drastically inhibited plant growth and caused abnormal vegetative and reproductive organ development. The Atasf1ab mutant plants exhibit cell number reduction, S-phase delay/arrest, and reduced polyploidy levels. Selective up-regulation of expression of a subset of genes, including those involved in S-phase checkpoints and the @entity17748 gene at the G   -to-M transition, was observed in Atasf1ab. Furthermore, the Atasf1ab-triggered replication fork stalling constitutively activates the DNA damage checkpoint and repair genes, including ATM, ATR, @entity72278 and @entity72279 as well as several genes of the homologous recombination (HR) pathway but not genes of the non-homologous end joining (NHEJ) pathway. In spite of the activation of repair genes, an increased level of DNA damage was detected in Atasf1ab, suggesting that defects in the mutant largely exceed the available capacity of the repair machinery. Taken together, our study establishes crucial roles for the @entity40312 and @entity40313 genes in chromatin replication, maintenance of genome integrity and cell proliferation during plant development.
