RESUMO
Root hair growth dramatically expands the root surface area, thus facilitating water and nutrient uptake. Until recently, the molecular mechanism underlying root hair growth was unknown. Recent studies have revealed that the transcription factor ROOT HAIR DEFECTIVE 6 LIKE 4 (RSL4) coordinates hormonal, environmental, and developmental factors to trigger polar growth.
Assuntos
Raízes de Plantas/metabolismo , Fatores de Transcrição/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Regulação da Expressão Gênica de Plantas/genética , Regulação da Expressão Gênica de Plantas/fisiologia , Raízes de Plantas/genética , Fatores de Transcrição/genéticaRESUMO
Root hair polar growth is endogenously controlled by auxin and sustained by oscillating levels of reactive oxygen species (ROS). These cells extend several hundred-fold their original size toward signals important for plant survival. Although their final cell size is of fundamental importance, the molecular mechanisms that control it remain largely unknown. Here we show that ROS production is controlled by the transcription factor RSL4, which in turn is transcriptionally regulated by auxin through several auxin response factors (ARFs). In this manner, auxin controls ROS-mediated polar growth by activating RSL4, which then up-regulates the expression of genes encoding NADPH oxidases (also known as RESPIRATORY BURST OXIDASE HOMOLOG proteins) and class III peroxidases, which catalyze ROS production. Chemical or genetic interference with ROS balance or peroxidase activity affects root hair final cell size. Overall, our findings establish a molecular link between auxin and ROS-mediated polar root hair growth.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Ácidos Indolacéticos/metabolismo , Proteínas de Arabidopsis/genética , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Regulação da Expressão Gênica de Plantas , NADPH Oxidases/metabolismo , Peroxidases/metabolismo , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Fatores de Transcrição/metabolismoRESUMO
Root hairs are single cells that develop by tip growth, a process shared with pollen tubes, axons, and fungal hyphae. However, structural plant cell walls impose constraints to accomplish tip growth. In addition to polysaccharides, plant cell walls are composed of hydroxyproline-rich glycoproteins (HRGPs), which include several groups of O-glycoproteins, including extensins (EXTs). Proline hydroxylation, an early post-translational modification (PTM) of HRGPs catalyzed by prolyl 4-hydroxylases (P4Hs), defines their subsequent O-glycosylation sites. In this work, our genetic analyses prove that P4H5, and to a lesser extent P4H2 and P4H13, are pivotal for root hair tip growth. Second, we demonstrate that P4H5 has in vitro preferred specificity for EXT substrates rather than for other HRGPs. Third, by P4H promoter and protein swapping approaches, we show that P4H2 and P4H13 have interchangeable functions but cannot replace P4H5. These three P4Hs are shown to be targeted to the secretory pathway, where P4H5 forms dimers with P4H2 and P4H13. Finally, we explore the impact of deficient proline hydroxylation on the cell wall architecture. Taken together, our results support a model in which correct peptidyl-proline hydroxylation on EXTs, and possibly in other HRGPs, is required for proper cell wall self-assembly and hence root hair elongation in Arabidopsis thaliana.