Masubelele Nompumelelo H, Dewitte Walter, Menges Margit, Maughan Spencer, Collins Carl, Huntley Rachael, Nieuwland Jeroen, Scofield Simon, Murray James A H
Institute of Biotechnology, University of Cambridge, Tennis Court Road, CB2 1QT Cambridge, United Kingdom.
Proc Natl Acad Sci U S A. 2005 Oct 25;102(43):15694-9. doi: 10.1073/pnas.0507581102. Epub 2005 Oct 14.
Seeds provide survival and dispersal capabilities by protecting the dormant mature plant embryo. Germination and resumption of development under favourable conditions requires the reinitiation of cell growth and division through poorly understood processes. Here we show that four phases of cell division activation during germination in Arabidopsis are related to external morphological changes. Cell division initiates in the root apical meristem (RAM) before root protrusion, followed by sequential activation of cell division in the cotyledons, shoot apical meristem (SAM), and secondary meristems. Major changes in transcript levels of >2,000 genes precede root emergence, including expression peaks of six D-type (CYCD) and two A-type cyclins. Two further CYCDs are activated later with the SAM. Early activated CYCDs play key roles in regulating the extent of cell division, because loss-of-function alleles of early CYCDs display reduced division activation and consequential delayed root emergence. Conversely, elevation of early CYCDs increases cell cycle activation in the RAM and promotes embryonic root (radicle) protrusion, whereas a later-acting CYCD does not. These phenotypes, together with their overlapping expression domains, support a cumulative action of a subset of CYCDs in cell cycle reactivation, rather than a complete functional redundancy. This analysis reveals a phenotype associated with loss-of-function of a plant cyclin and demonstrates that D-type cyclins regulate cell cycle reentry during meristem activation to promote successful germination and early seedling growth.
种子通过保护处于休眠状态的成熟植物胚，提供了生存和传播能力。在有利条件下种子萌发和恢复生长需要通过尚不明确的过程重新启动细胞生长和分裂。在此，我们表明拟南芥种子萌发过程中细胞分裂激活的四个阶段与外部形态变化相关。在根突出之前，细胞分裂在根尖分生组织（RAM）中启动，随后子叶、茎尖分生组织（SAM）和次生分生组织中的细胞分裂依次被激活。超过2000个基因的转录水平在根出现之前发生重大变化，包括六个D型（CYCD）和两个A型细胞周期蛋白的表达峰值。另外两个CYCDs随后在SAM中被激活。早期激活的CYCDs在调节细胞分裂程度方面起关键作用，因为早期CYCDs的功能缺失等位基因表现出细胞分裂激活减少以及随之而来的根出现延迟。相反，早期CYCDs的升高会增加RAM中的细胞周期激活，并促进胚根突出，而后期起作用的CYCD则没有这种作用。这些表型及其重叠的表达域，支持了CYCDs的一个子集在细胞周期重新激活中的累积作用，而不是完全的功能冗余。该分析揭示了一种与植物细胞周期蛋白功能丧失相关的表型，并表明D型细胞周期蛋白在分生组织激活过程中调节细胞周期重新进入，以促进成功萌发和早期幼苗生长。
