The Rockefeller University, New York, New York 10065.
The Rockefeller University, New York, New York 10065
Plant Cell. 2018 Feb;30(2):429-446. doi: 10.1105/tpc.17.00759. Epub 2018 Jan 24.
The cyclin-dependent kinase CDK1 is essential for mitosis in fungi and animals. Plant genomes contain the CDK1 ortholog CDKA and a plant kingdom-specific relative, CDKB. The green alga has a long G1 growth period followed by rapid cycles of DNA replication and cell division. We show that null alleles of CDKA extend the growth period prior to the first division cycle and modestly extend the subsequent division cycles, but do not prevent cell division, indicating at most a minor role for the CDK1 ortholog in mitosis in Chlamydomonas. A null allele of cyclin A has a similar though less extreme phenotype. In contrast, both CDKB and cyclin B are essential for mitosis. CDK kinase activity measurements imply that the predominant in vivo complexes are probably cyclin A-CDKA and cyclin B-CDKB. We propose a negative feedback loop: CDKA activates cyclin B-CDKB. Cyclin B-CDKB in turn promotes mitotic entry and inactivates cyclin A-CDKA. Cyclin A-CDKA and cyclin B-CDKB may redundantly promote DNA replication. We show that the anaphase-promoting complex is required for inactivation of both CDKA and CDKB and is essential for anaphase. These results are consistent with findings in and may delineate the core of plant kingdom cell cycle control that, compared with the well-studied yeast and animal systems, exhibits deep conservation in some respects and striking divergence in others.
细胞周期蛋白依赖性激酶 CDK1 对于真菌和动物的有丝分裂是必不可少的。植物基因组包含 CDK1 直系同源物 CDKA 和一个植物界特有的相对物 CDKB。绿藻具有较长的 G1 生长期，随后是快速的 DNA 复制和细胞分裂周期。我们表明，CDKA 的 null 等位基因延长了第一个分裂周期之前的生长周期，并适度延长了随后的分裂周期，但不会阻止细胞分裂，表明 CDK1 直系同源物在衣藻的有丝分裂中最多起次要作用。cyclin A 的 null 等位基因具有类似但不太极端的表型。相比之下，CDKB 和 cyclin B 对于有丝分裂都是必不可少的。CDK 激酶活性测量表明，占主导地位的体内复合物可能是 cyclin A-CDKA 和 cyclin B-CDKB。我们提出了一个负反馈回路：CDKA 激活 cyclin B-CDKB。cyclin B-CDKB 反过来又促进有丝分裂进入并使 cyclin A-CDKA 失活。cyclin A-CDKA 和 cyclin B-CDKB 可能冗余地促进 DNA 复制。我们表明，后期促进复合物对于 CDKA 和 CDKB 的失活都是必需的，并且对于后期是必不可少的。这些结果与在 中发现的结果一致，并且可能描绘了植物王国细胞周期控制的核心，与研究充分的酵母和动物系统相比，在某些方面表现出深度保守，而在其他方面则表现出惊人的差异。
