Histidine kinase homologs that act as cytokinin receptors possess overlapping functions in the regulation of shoot and root growth in Arabidopsis
Histidine kinase homologs that act as cytokinin receptors possess overlapping functions in the regulation of shoot and root growth in Arabidopsis
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DOI：
10.1105/tpc.021477
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发表时间：
2004-06-01
期刊：
影响因子：
11.6
通讯作者：
Ueguchi, C
中科院分区：
文献类型：
--
作者：
Nishimura, C;Ohashi, Y;Ueguchi, C
细胞分裂素是植物激素，在植物生长发育的各个方面都起着重要的作用。虽然外源性细胞分裂素对细胞增殖和分化的功能意义已被充分证明，但内源性细胞分裂素的生物学作用在很大程度上仍然未知。最近在拟南芥中发现的拟南芥组氨酸激酶4（AHK 4）/CRE 1/WOL细胞分裂素受体强烈表明细胞对细胞分裂素的反应涉及一个双组分信号转导系统。然而，突变体中缺乏明显的表型，可能是因为遗传冗余，使我们无法确定细胞分裂素受体在植物中的作用。为了深入了解三个AHK基因AHK 2，AHK 3和AHK 4的分子功能，在这项研究中，我们确定了AHK 2和AHK 3基因的突变等位基因，这两个基因都编码与AHK 4密切相关的传感器组氨酸激酶，并构建了一组多个AHK突变体。将外源细胞分裂素应用于所得菌株揭示了AHK 2和AHK 3都作为细胞分裂素信号传导的正调节剂起作用，类似于AHK 4。ahk 2 ahk 4和ahk 3 ahk 4双突变体和ahk单突变体生长正常，而ahk 2 ahk 3双突变体表现出半矮生表型，如叶大小减小和茎长度减少。ahk 2 ahk 3 ahk 4三突变体的生长发育在营养生长期的根、叶和生殖生长期的茎分生组织中均受到明显抑制。我们发现生长的抑制与细胞分生组织活性的降低有关。涉及AHK：P-葡萄糖醛酸酶融合基因的表达分析表明，AHK基因在胚后生长和发育过程中的各种组织中普遍表达。因此，我们的研究结果强烈表明，AHK基因的主要功能，和那些内源性细胞分裂素，是触发细胞分裂和维持细胞的分生能力，以防止随后的分化，直到有足够数量的细胞积累在器官发生。
Cytokinins are plant hormones that may play essential and crucial roles in various aspects of plant growth and development. Although the functional significance of exogenous cytokinins as to the proliferation and differentiation of cells has been well documented, the biological roles of endogenous cytokinins have remained largely unknown. The recent discovery of the Arabidopsis Histidine Kinase 4 (AHK4)/CRE1/WOL cytokinin receptor in Arabidopsis thaliana strongly suggested that the cellular response to cytokinins involves a two-component signal transduction system. However, the lack of an apparent phenotype in the mutant, presumably because of genetic redundancy, prevented us from determining the in planta roles of the cytokinin receptor. To gain insight into the molecular functions of the three AHK genes AHK2, AHK3, and AHK4 in this study, we identified mutational alleles of the AHK2 and AHK3 genes, both of which encode sensor histidine kinases closely related to AHK4, and constructed a set of multiple ahk mutants. Application of exogenous cytokinins to the resultant strains revealed that both AHK2 and AHK3 function as positive regulators for cytokinin signaling similar to AHK4. The ahk2 ahk4 and ahk3 ahk4 double mutants and the ahk single mutants grew normally, whereas the ahk2 ahk3 double mutants exhibited a semidwarf phenotype as to shoots, such as a reduced leaf size and a reduced influorescence stem length. The growth and development of the ahk2 ahk3 ahk4 triple mutant were markedly inhibited in various tissues and organs, including the roots and leaves in the vegetative growth phase and the influorescence meristem in the reproductive phase. We showed that the inhibition of growth is associated with reduced meristematic activity of cells. Expression analysis involving AHK:P-glucuronidase fusion genes suggested that the AHK genes are expressed ubiquitously in various tissues during postembryonic growth and development. Our results thus strongly suggest that the primary functions of AHK genes, and those of endogenous cytokinins, are triggering of the cell division and maintenance of the meristematic competence of cells to prevent subsequent differentiation until a sufficient number of cells has accumulated during organogenesis.