Abstract
Reactive oxygen species (ROS), a type of oxygen monoelectronic reduction product, have a higher chemical activity than O2. Although ROS pose potential risks to all organisms via inducing oxidative stress, indispensable role of ROS in individual development cannot be ignored. Among them, the role of ROS in the model plant Arabidopsis thaliana is deeply studied. Mounting evidence suggests that ROS are essential for root and root hair development. In the present review, we provide an updated perspective on the latest research progress pertaining to the role of ROS in the precise regulation of root stem cell maintenance and differentiation, redox regulation of the cell cycle, and root hair initiation during root growth. Among the different types of ROS, O2 •− and H2O2 have been extensively investigated, and they exhibit different gradient distributions in the roots. The concentration of O2 •− decreases along a gradient from the meristem to the transition zone and the concentration of H2O2 decreases along a gradient from the differentiation zone to the elongation zone. These gradients are regulated by peroxidases, which are modulated by the UPBEAT1 (UPB1) transcription factor. In addition, multiple transcriptional factors, such as APP1, ABO8, PHB3, and RITF1, which are involved in the brassinolide signaling pathway, converge as a ROS signal to regulate root stem cell maintenance. Furthermore, superoxide anions (O2 •−) are generated from the oxidation in mitochondria, ROS produced during plasmid metabolism, H2O2 produced in apoplasts, and catalysis of respiratory burst oxidase homolog (RBOH) in the cell membrane. Furthermore, ROS can act as a signal to regulate redox status, which regulates the expression of the cell-cycle components CYC2;3, CYCB1;1, and retinoblastoma-related protein, thereby controlling the cell-cycle progression. In the root maturation zone, the epidermal cells located in the H cell position emerge to form hair cells, and plant hormones, such as auxin and ethylene regulate root hair formation via ROS. Furthermore, ROS accumulation can influence hormone signal transduction and vice versa. Data about the association between nutrient stress and ROS signals in root hair development are scarce. However, the fact that ROBHC/RHD2 or RHD6 is specifically expressed in root hair cells and induced by nutrients, may explain the relationship. Future studies should focus on the regulatory mechanisms underlying root hair development via the interactions of ROS with hormone signals and nutrient components.
Highlights
In the Earth’s distant past, the rapid accumulation of oxygen in the atmosphere was an important event for the evolution of multicellular molecular processes (Jeltsch, 2013)
Mutations in the oxidation sites in the proteins aforementioned such as BRASSINAZOLE-RESISTANT 1 (BZR1) and BRI1-EMS-SUPPRESSOR 1 (BES1), or a reduction in endogenous reactive oxygen species (ROS) content can significantly impair the functions of BZR1 and BES1 in regulating gene expression and various biological processes, including quiescent center (QC) cell division in the roots (Vilarrasa-Blasi et al, 2014; Yang et al, 2018; Surgun-Acar and Zemheri-Navruz, 2019)
The study of root hair cells shows that the polarized growth of cells depends on the local accumulation of ROS produced by NADPH oxidase (NOX) (Foreman et al, 2003)
Summary
In the Earth’s distant past, the rapid accumulation of oxygen in the atmosphere was an important event for the evolution of multicellular molecular processes (Jeltsch, 2013). GRADIENT DISTRIBUTION OF ROS REGULATES ROOT STEM CELL DIFFERENTIATION This leads to the establishment of a hypothetical relationship between ROS signals and PLT-mediated maintenance and regulation of the root stem cell niche (Figure 2) (Yang et al, 2014; Tsukagoshi, 2016).
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