Plant bodies are built from immobile cells, making the regulation of cell expansion essential for growth, development, and adaptation. In roots, cell elongation executes the movement of the root tips through the soil. This process is tightly controlled by numerous signaling pathways. Among these, gibberellin and auxin signaling stand out for their contrasting effects on root growth, interacting through complex cross talk at multiple regulatory levels. Here, we reveal the molecular basis of the auxin-gibberellin cross talk in the model plant Arabidopsis thaliana. We show that the auxin signaling pathway steers the expression of GIBBERELLIN 2-OXIDASES (GA2OXs), key gibberellin-deactivating enzymes in the root elongation zone (EZ). GA2OXs are negative regulators of root cell elongation; GA2OX8 overexpression decreases gibberellin levels and inhibits root cell elongation; in contrast, the ga2ox heptuple mutant roots show elevated gibberellin levels in the EZ and grow longer roots. Intriguingly, shoot-derived auxin can regulate GA2OX6 and GA2OX8 expression in roots, linking systemic auxin signaling to local gibberellin level modulation. Together, our findings identify GA2OX6 and GA2OX8 enzymes as key mediators of auxin-gibberellin cross talk, providing insights into their roles in root elongation. These results expand our understanding of how auxin integrates with gibberellin signaling to coordinate root development and growth dynamics.

• Klíčová slova
• Arabidopsis, auxin, gibberellin, root,
• MeSH
• Arabidopsis * růst a vývoj   metabolismus   genetika   enzymologie   MeSH
• gibereliny * metabolismus   MeSH
• kořeny rostlin * růst a vývoj   metabolismus   genetika   MeSH
• kyseliny indoloctové * metabolismus   MeSH
• oxygenasy se smíšenou funkcí * metabolismus   genetika   MeSH
• proteiny huseníčku * metabolismus   genetika   MeSH
• regulace genové exprese u rostlin MeSH
• regulátory růstu rostlin metabolismus   MeSH
• signální transdukce MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• gibberellin 2-dioxygenase MeSH Prohlížeč
• gibereliny * MeSH
• kyseliny indoloctové * MeSH
• oxygenasy se smíšenou funkcí * MeSH
• proteiny huseníčku * MeSH
• regulátory růstu rostlin MeSH

The vegetative juvenile-to-adult transition (vegetative phase change) is a critical phase in plant development, the timing of which is controlled by the highly conserved age pathway, comprising the miR156/miR157-SPL module and the downstream miR172-AP2-like module, and is modulated by exogenous and endogenous cues. The phytohormones cytokinin (CK) and gibberellin (GA) have been described to both alter miR172 levels, most probably by regulating SPL activity. In this study, we establish an epistatic relation between CK and GA, in which CK action depends on GA, contrasting with the antagonistic nature described previously for CK-GA crosstalk. We show that CK positively affects GA biosynthesis during Arabidopsis vegetative development and depends on the GA biosynthetic enzymes GA3ox1 and GA3ox2 to modify the appearance of abaxial trichomes as well as leaf shape, both hallmarks of vegetative phase change. Downstream of CK, epidermal identity is regulated in dependence of SPL transcription factors, the GA signaling repressors GAI and RGA and the miR172-targets TOE1 and TOE2. Notably, genetic analysis revealed that GA regulates this process also CK-independently. Furthermore, our data from genetic analyses suggests that CK affects leaf shape through other GA signaling components and AP2-like transcription factors rather than SPLs. Hence, CK differentially regulates several aspects of vegetative phase change. The work contributes to the understanding of vegetative phase change regulation as well as phytohormone crosstalk in general.

• MeSH
• Arabidopsis * metabolismus   genetika   růst a vývoj   MeSH
• cytokininy * metabolismus   MeSH
• gibereliny * metabolismus   MeSH
• jaderné proteiny MeSH
• listy rostlin metabolismus   růst a vývoj   MeSH
• mikro RNA metabolismus   genetika   MeSH
• oxygenasy se smíšenou funkcí metabolismus   genetika   MeSH
• proteiny huseníčku metabolismus   genetika   MeSH
• regulace genové exprese u rostlin MeSH
• regulátory růstu rostlin metabolismus   MeSH
• represorové proteiny MeSH
• signální transdukce MeSH
• transkripční faktory metabolismus   genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• cytokininy * MeSH
• GAI protein, Arabidopsis MeSH Prohlížeč
• gibereliny * MeSH
• jaderné proteiny MeSH
• mikro RNA MeSH
• Mirn156 microRNA, Arabidopsis MeSH Prohlížeč
• oxygenasy se smíšenou funkcí MeSH
• proteiny huseníčku MeSH
• regulátory růstu rostlin MeSH
• represorové proteiny MeSH
• RGA protein, Arabidopsis MeSH Prohlížeč
• SPL protein, Arabidopsis MeSH Prohlížeč
• transkripční faktory MeSH

Linear modelling approaches detected significant gradients in organ growth and patterning across early flowers of the Arabidopsis inflorescence and uncovered evidence of new roles for gibberellin in floral development. Most flowering plants, including the genetic model Arabidopsis thaliana, produce multiple flowers in sequence from a reproductive shoot apex to form a flower spike (inflorescence). The development of individual flowers on an Arabidopsis inflorescence has typically been considered as highly stereotypical and uniform, but this assumption is contradicted by the existence of mutants with phenotypes visible in early flowers only. This phenomenon is demonstrated by mutants partially impaired in the biosynthesis of the phytohormone gibberellin (GA), in which floral organ growth is retarded in the first flowers to be produced but has recovered spontaneously by the 10th flower. We presently lack systematic data from multiple flowers across the Arabidopsis inflorescence to explain such changes. Using mutants of the GA 20-OXIDASE (GA20ox) GA biosynthesis gene family to manipulate endogenous GA levels, we investigated the dynamics of changing floral organ growth across the early Arabidopsis inflorescence (flowers 1-10). Modelling of floral organ lengths identified a significant, GA-independent gradient of increasing stamen length relative to the pistil in the wild-type inflorescence that was separable from other, GA-dependent effects. It was also found that the first flowers exhibited unstable organ patterning in contrast to later flowers and that this instability was prolonged by exogenous GA treatment. These findings indicate that the development of individual flowers is influenced by hitherto unknown factors acting across the inflorescence and also suggest novel functions for GA in floral patterning.

• Klíčová slova
• Arabidopsis, Flower, Gibberellin (GA), Inflorescence, Modelling,
• MeSH
• Arabidopsis genetika   růst a vývoj   MeSH
• fenotyp MeSH
• gibereliny metabolismus   farmakologie   MeSH
• inflorescentia genetika   růst a vývoj   MeSH
• květy genetika   růst a vývoj   MeSH
• lineární modely MeSH
• meristém genetika   růst a vývoj   MeSH
• mutace MeSH
• oxygenasy se smíšenou funkcí genetika   metabolismus   MeSH
• proteiny huseníčku genetika   metabolismus   MeSH
• regulátory růstu rostlin metabolismus   farmakologie   MeSH
• signální transdukce MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• gibberellin, 2-oxoglutarate-oxygen oxidoreductase (20-hydroxylating, oxidizing) MeSH Prohlížeč
• gibereliny MeSH
• oxygenasy se smíšenou funkcí MeSH
• proteiny huseníčku MeSH
• regulátory růstu rostlin MeSH