Arabidopsis homologues of the histone chaperone ASF1 are crucial for chromatin replication and cell proliferation in plant development.
Arabidopsis homologues of the histone chaperone ASF1 are crucial for chromatin replication and cell proliferation in plant development.
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DOI：
10.1111/j.1365-313x.2011.04504.x
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发表时间：
2011-05
期刊：
影响因子：
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通讯作者：
Yan Zhu;Minjie Weng;Yue Yang;Chi Zhang;Ziyu Li;W. Shen;A. Dong
中科院分区：
文献类型：
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作者：
Yan Zhu;Minjie Weng;Yue Yang;Chi Zhang;Ziyu Li;W. Shen;A. Dong
抗沉默功能蛋白1（ASF 1）是一种进化上保守的组蛋白伴侣。在酵母和动物中的研究表明，ASF 1蛋白在各种基于染色质的过程中发挥重要作用，包括基因转录，DNA复制和修复。虽然在拟南芥基因组中发现了两个编码ASF 1同源物的基因AtASF 1A和AtASF 1B，但尚未研究它们的功能。在这里，我们报告，AtASF 1A和AtASF 1B蛋白结合组蛋白H3，并定位在细胞质和细胞核。AtASF 1A或AtASF 1B的功能丧失并没有表现出明显的缺陷，而同时敲低这两个基因的双突变体Atasf 1ab大大抑制植物生长，并引起异常的营养和生殖器官发育。Atasf 1ab突变体植物表现出细胞数量减少，S期延迟/停滞，和降低的多倍体水平。在Atasf 1ab中观察到一组基因表达的选择性上调，包括参与S期检查点的基因和CYCB 1;1基因在G期向M期转变的基因。此外，Atasf 1ab触发的复制叉停滞组成型激活DNA损伤检查点和修复基因，包括ATM、ATR、PARP 1和PARP 2以及同源重组（HR）途径的几个基因，但不激活非同源末端连接（NHEJ）途径的基因。尽管修复基因被激活，但在Atasf 1ab中检测到DNA损伤水平增加，这表明突变体中的缺陷大大超过了修复机制的可用能力。综上所述，我们的研究确定了AtASF 1A和AtASF 1B基因在植物发育过程中染色质复制，基因组完整性维护和细胞增殖中的关键作用。
Anti-silencing function1 (ASF1) is an evolutionarily conserved histone chaperone. Studies in yeast and animals indicate that ASF1 proteins play important roles in various chromatin-based processes, including gene transcription, DNA replication and repair. While two genes encoding ASF1 homologues, AtASF1A and AtASF1B, are found in the Arabidopsis genome, their function has not been studied. Here we report that both AtASF1A and AtASF1B proteins bind histone H3, and are localized in the cytoplasm and the nucleus. Loss-of-function of either AtASF1A or AtASF1B 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 CYCB1;1 gene at the G₂-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, PARP1 and PARP2 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 AtASF1A and AtASF1B genes in chromatin replication, maintenance of genome integrity and cell proliferation during plant development.