Cytokinins are required for symbiotic nodule development in legumes, and cytokinin signaling responses occur locally in nodule primordia and in developing nodules. Here, we show that the Lotus japonicus Ckx3 cytokinin oxidase/dehydrogenase gene is induced by Nod factor during the early phase of nodule initiation. At the cellular level, pCkx3::YFP reporter-gene studies revealed that the Ckx3 promoter is active during the first cortical cell divisions of the nodule primordium and in growing nodules. Cytokinin measurements in ckx3 mutants confirmed that CKX3 activity negatively regulates root cytokinin levels. Particularly, tZ and DHZ type cytokinins in both inoculated and uninoculated roots were elevated in ckx3 mutants, suggesting that these are targets for degradation by the CKX3 cytokinin oxidase/dehydrogenase. The effect of CKX3 on the positive and negative roles of cytokinin in nodule development, infection and regulation was further clarified using ckx3 insertion mutants. Phenotypic analysis indicated that ckx3 mutants have reduced nodulation, infection thread formation and root growth. We also identify a role for cytokinin in regulating nodulation and nitrogen fixation in response to nitrate as ckx3 phenotypes are exaggerated at increased nitrate levels. Together, these findings show that cytokinin accumulation is tightly regulated during nodulation in order to balance the requirement for cell divisions with negative regulatory effects of cytokinin on infection events and root development.
- MeSH
- alely MeSH
- buněčná diferenciace MeSH
- cytokininy metabolismus MeSH
- dusičnany metabolismus MeSH
- fenotyp MeSH
- fixace dusíku genetika MeSH
- fylogeneze MeSH
- homeostáza * MeSH
- kořenové hlízky rostlin genetika růst a vývoj MeSH
- Lotus enzymologie genetika růst a vývoj MeSH
- meristém cytologie růst a vývoj MeSH
- mutace genetika MeSH
- oxidoreduktasy genetika metabolismus MeSH
- promotorové oblasti (genetika) MeSH
- rostlinné geny MeSH
- rostlinné proteiny genetika metabolismus MeSH
- tvorba kořenových hlízek genetika MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Bud outgrowth is controlled by environmental and endogenous factors. Through the use of the photosynthesis inhibitor norflurazon and of masking experiments, evidence is given here that light acts mainly as a morphogenic signal in the triggering of bud outgrowth and that initial steps in the light signaling pathway involve cytokinins (CKs). Indeed, in rose (Rosa hybrida), inhibition of bud outgrowth by darkness is suppressed solely by the application of CKs. In contrast, application of sugars has a limited effect. Exposure of plants to white light (WL) induces a rapid (after 3-6 h of WL exposure) up-regulation of CK synthesis (RhIPT3 and RhIPT5), of CK activation (RhLOG8), and of CK putative transporter RhPUP5 genes and to the repression of the CK degradation RhCKX1 gene in the node. This leads to the accumulation of CKs in the node within 6 h and in the bud at 24 h and to the triggering of bud outgrowth. Molecular analysis of genes involved in major mechanisms of bud outgrowth (strigolactone signaling [RwMAX2], metabolism and transport of auxin [RhPIN1, RhYUC1, and RhTAR1], regulation of sugar sink strength [RhVI, RhSUSY, RhSUC2, and RhSWEET10], and cell division and expansion [RhEXP and RhPCNA]) reveal that, when supplied in darkness, CKs up-regulate their expression as rapidly and as intensely as WL Additionally, up-regulation of CKs by WL promotes xylem flux toward the bud, as evidenced by Methylene Blue accumulation in the bud after CK treatment in the dark. Altogether, these results suggest that CKs are initial components of the light signaling pathway that controls the initiation of bud outgrowth.
- MeSH
- biologické modely MeSH
- časové faktory MeSH
- cytokininy metabolismus farmakologie MeSH
- meristém genetika růst a vývoj metabolismus MeSH
- polymerázová řetězová reakce s reverzní transkripcí MeSH
- regulace genové exprese u rostlin účinky léků účinky záření MeSH
- regulátory růstu rostlin metabolismus farmakologie MeSH
- Rosa genetika růst a vývoj metabolismus MeSH
- rostlinné proteiny genetika metabolismus MeSH
- signální transdukce účinky léků genetika účinky záření MeSH
- světlo * MeSH
- tma MeSH
- výhonky rostlin genetika růst a vývoj metabolismus MeSH
- vývojová regulace genové exprese účinky léků účinky záření MeSH
- xylém genetika růst a vývoj metabolismus MeSH
- Publikační typ
- časopisecké články MeSH