Franco-Zorrilla José Manuel, Martín Ana Carmen, Leyva Antonio, Paz-Ares Javier
Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, Campus de Cantoblanco 28049, Madrid, Spain.
Plant Physiol. 2005 Jun;138(2):847-57. doi: 10.1104/pp.105.060517. Epub 2005 May 27.
Cytokinins control key processes during plant growth and development, and cytokinin receptors CYTOKININ RESPONSE 1/WOODEN LEG/ARABIDOPSIS HISTIDINE KINASE 4 (CRE1/WOL/AHK4), AHK2, and AHK3 have been shown to play a crucial role in this control. The involvement of cytokinins in signaling the status of several nutrients, such as sugar, nitrogen, sulfur, and phosphate (Pi), has also been highlighted, although the full physiological relevance of this role remains unclear. To gain further insights into this aspect of cytokinin action, we characterized a mutant with reduced sensitivity to cytokinin repression of a Pi starvation-responsive reporter gene and show it corresponds to AHK3. As expected, ahk3 displayed reduced responsiveness to cytokinin in callus proliferation and plant growth assays. In addition, ahk3 showed reduced cytokinin repression of several Pi starvation-responsive genes and increased sucrose sensitivity. These effects of the ahk3 mutation were especially evident in combination with the cre1 mutation, indicating partial functional redundancy between these receptors. We examined the effect of these mutations on Pi-starvation responses and found that the double mutant is not significantly affected in long-distance systemic repression of these responses. Remarkably, we found that expression of many Pi-responsive genes is stimulated by sucrose in shoots and to a lesser extent in roots, and the sugar effect in shoots of Pi-starved plants was particularly enhanced in the cre1 ahk3 double mutant. Altogether, these results indicate the existence of multidirectional cross regulation between cytokinin, sugar, and Pi-starvation signaling, thus underlining the role of cytokinin signaling in nutrient sensing and the relative importance of Pi-starvation signaling in the control of plant metabolism and development.
细胞分裂素控制着植物生长发育过程中的关键进程，细胞分裂素受体细胞分裂素响应1/木腿/拟南芥组氨酸激酶4（CRE1/WOL/AHK4）、AHK2和AHK3已被证明在这种调控中起着至关重要的作用。细胞分裂素参与多种养分（如糖、氮、硫和磷酸盐（Pi））状态的信号传导也已得到强调，尽管这一作用的完整生理相关性仍不清楚。为了进一步深入了解细胞分裂素作用的这一方面，我们对一个对Pi饥饿响应报告基因的细胞分裂素抑制敏感性降低的突变体进行了表征，并表明它对应于AHK3。正如预期的那样，在愈伤组织增殖和植物生长试验中，ahk3对细胞分裂素的反应性降低。此外，ahk3对几个Pi饥饿响应基因的细胞分裂素抑制作用降低，对蔗糖的敏感性增加。ahk3突变的这些效应在与cre1突变结合时尤为明显，表明这些受体之间存在部分功能冗余。我们研究了这些突变对Pi饥饿响应的影响，发现双突变体在这些响应的长距离系统抑制中没有受到显著影响。值得注意的是，我们发现许多Pi响应基因的表达在地上部受到蔗糖的刺激，在根部受到的刺激较小，并且Pi饥饿植物地上部的糖效应在cre1 ahk3双突变体中尤其增强。总之，这些结果表明细胞分裂素、糖和Pi饥饿信号之间存在多向交叉调控，从而强调了细胞分裂素信号在养分感知中的作用以及Pi饥饿信号在植物代谢和发育控制中的相对重要性。
