Interaction between phosphate-starvation, sugar, and cytokinin signaling in Arabidopsis and the roles of cytokinin receptors CRE1/AHK4 and AHK3.
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.
Franco-Zorrilla
José Manuel
JM
Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, Campus de Cantoblanco 28049, Madrid, Spain.
Martín
Ana Carmen
AC
Leyva
Antonio
A
Paz-Ares
Javier
J
D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000502:physiology*; D002241:Carbohydrates / Q000502:physiology*; D003583:Cytokinins / Q000502:physiology*; D015536:Down-Regulation; D018506:Gene Expression Regulation, Plant; D000071677:Histidine Kinase; D010710:Phosphates / Q000502:physiology*; D018517:Plant Roots / Q000502:physiology; D018520:Plant Shoots / Q000502:physiology; D011494:Protein Kinases / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000502:physiology*; D015398:Signal Transduction
D029681:Arabidopsis Proteins; D002241:Carbohydrates; D003583:Cytokinins; D010710:Phosphates; D011956:Receptors, Cell Surface; D011494:Protein Kinases; D000071677:Histidine Kinase; C000605492:AHK2 protein, Arabidopsis; C000605493:AHK3 protein, Arabidopsis; C421783:WOL protein, Arabidopsis