School of Biosciences, Cardiff University, Cardiff CF10 3AT, UK.
BMC Plant Biol. 2012 Mar 27;12:45. doi: 10.1186/1471-2229-12-45.
Entry into mitosis is regulated by cyclin dependent kinases that in turn are phosphoregulated. In most eukaryotes, phosphoregulation is through WEE1 kinase and CDC25 phosphatase. In higher plants a homologous CDC25 gene is unconfirmed and hence the mitotic inducer Schizosaccharomyces pombe (Sp) cdc25 has been used as a tool in transgenic plants to probe cell cycle function. Expression of Spcdc25 in tobacco BY-2 cells accelerates entry into mitosis and depletes cytokinins; in whole plants it stimulates lateral root production. Here we show, for the first time, that alterations to cytokinin and ethylene signaling explain the rooting phenotype elicited by Spcdc25 expression in Arabidopsis.
Expressing Spcdc25 in Arabidopsis results in increased formation of lateral and adventitious roots, a reduction of primary root width and more isodiametric cells in the root apical meristem (RAM) compared with wild type. Furthermore it stimulates root morphogenesis from hypocotyls when cultured on two way grids of increasing auxin and cytokinin concentrations. Microarray analysis of seedling roots expressing Spcdc25 reveals that expression of 167 genes is changed by > 2-fold. As well as genes related to stress responses and defence, these include 19 genes related to transcriptional regulation and signaling. Amongst these was the up-regulation of genes associated with ethylene synthesis and signaling. Seedlings expressing Spcdc25 produced 2-fold more ethylene than WT and exhibited a significant reduction in hypocotyl length both in darkness or when exposed to 10 ppm ethylene. Furthermore in Spcdc25 expressing plants, the cytokinin receptor AHK3 was down-regulated, and endogenous levels of iPA were reduced whereas endogeous IAA concentrations in the roots increased.
We suggest that the reduction in root width and change to a more isodiametric cell phenotype in the RAM in Spcdc25 expressing plants is a response to ethylene over-production. The increased rooting phenotype in Spcdc25 expressing plants is due to an increase in the ratio of endogenous auxin to cytokinin that is known to stimulate an increased rate of lateral root production. Overall, our data reveal important cross talk between cell division and plant growth regulators leading to developmental changes.
有丝分裂的进入受细胞周期蛋白依赖性激酶（CDK）的调控，而 CDK 又受磷酸化调控。在大多数真核生物中，磷酸化调节是通过 WEE1 激酶和 CDC25 磷酸酶实现的。在高等植物中，尚未确认同源的 CDC25 基因，因此裂殖酵母（Schizosaccharomyces pombe，Sp）cdc25 作为一种有丝分裂诱导剂已被用于转基因植物，以探测细胞周期功能。在烟草 BY-2 细胞中表达 Spcdc25 可加速有丝分裂的进入并耗尽细胞分裂素；在整株植物中，它会刺激侧根的产生。在这里，我们首次表明，细胞分裂素和乙烯信号的改变解释了 Spcdc25 在拟南芥中表达所引起的生根表型。
在拟南芥中表达 Spcdc25 会导致侧根和不定根的形成增加，主根宽度减小，根尖分生组织（RAM）中的等径细胞增多。此外，当在含有逐渐增加的生长素和细胞分裂素浓度的双向网格上培养时，它会刺激下胚轴的根形态发生。表达 Spcdc25 的幼苗根的微阵列分析显示，有 167 个基因的表达变化超过 2 倍。除了与应激反应和防御相关的基因外，这些基因还包括 19 个与转录调控和信号转导相关的基因。其中包括与乙烯合成和信号转导相关的基因上调。表达 Spcdc25 的幼苗比 WT 产生的乙烯多 2 倍，并且在黑暗或暴露于 10 ppm 乙烯时，下胚轴长度显著缩短。此外，在表达 Spcdc25 的植物中，细胞分裂素受体 AHK3 下调，内源 iPA 水平降低，而根部内源 IAA 浓度增加。
我们认为，在表达 Spcdc25 的植物中，RAM 中根宽度减小和更等径细胞表型的改变是由于乙烯过度产生所致。表达 Spcdc25 的植物中增加的生根表型是由于内源生长素与细胞分裂素的比例增加所致，已知这会刺激侧根产生率的增加。总的来说，我们的数据揭示了细胞分裂和植物生长调节剂之间的重要交叉对话，导致了发育变化。
