Auxins mediate various processes that are involved in plant growth and development in response to specific environmental conditions. Its proper spatio-temporal distribution that is driven by polar auxin transport machinery plays a crucial role in the wide range of auxins physiological effects. Numbers of approaches have been developed to either directly or indirectly monitor auxin distribution in vivo in order to elucidate the basis of its precise regulation. Herein, we provide an updated list of valuable techniques used for monitoring auxins in plants, with their utilities and limitations. Because the spatial and temporal resolutions of the presented approaches are different, their combination may provide a comprehensive outcome of auxin distribution in diverse developmental processes.

• Keywords
• auxin, auxin distribution, auxin signalling, auxin transport, direct visualization, indirect visualization, receptor, sensor,
• MeSH
• Arabidopsis metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Plant Development physiology   MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Indoleacetic Acids MeSH

Plant growth depends on stem cell niches in meristems. In the root apical meristem, the quiescent center (QC) cells form a niche together with the surrounding stem cells. Stem cells produce daughter cells that are displaced into a transit-amplifying (TA) domain of the root meristem. TA cells divide several times to provide cells for growth. SHORTROOT (SHR) and SCARECROW (SCR) are key regulators of the stem cell niche. Cytokinin controls TA cell activities in a dose-dependent manner. Although the regulatory programs in each compartment of the root meristem have been identified, it is still unclear how they coordinate one another. Here, we investigate how PHABULOSA (PHB), under the posttranscriptional control of SHR and SCR, regulates TA cell activities. The root meristem and growth defects in shr or scr mutants were significantly recovered in the shr phb or scr phb double mutant, respectively. This rescue in root growth occurs in the absence of a QC. Conversely, when the modified PHB, which is highly resistant to microRNA, was expressed throughout the stele of the wild-type root meristem, root growth became very similar to that observed in the shr; however, the identity of the QC was unaffected. Interestingly, a moderate increase in PHB resulted in a root meristem phenotype similar to that observed following the application of high levels of cytokinin. Our protoplast assay and transgenic approach using ARR10 suggest that the depletion of TA cells by high PHB in the stele occurs via the repression of B-ARR activities. This regulatory mechanism seems to help to maintain the cytokinin homeostasis in the meristem. Taken together, our study suggests that PHB can dynamically regulate TA cell activities in a QC-independent manner, and that the SHR-PHB pathway enables a robust root growth system by coordinating the stem cell niche and TA domain.

• MeSH
• Arabidopsis genetics   growth & development   MeSH
• Cell Division genetics   MeSH
• Cytokinins genetics   metabolism   MeSH
• DNA-Binding Proteins genetics   MeSH
• Phenotype MeSH
• Plants, Genetically Modified growth & development   MeSH
• Homeodomain Proteins biosynthesis   genetics   MeSH
• Homeostasis MeSH
• Plant Roots genetics   growth & development   MeSH
• Meristem genetics   growth & development   MeSH
• Stem Cell Niche genetics   MeSH
• Arabidopsis Proteins biosynthesis   genetics   metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Transcription Factors genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Names of Substances
• ARR10 protein, Arabidopsis MeSH Browser
• Cytokinins MeSH
• DNA-Binding Proteins MeSH
• Homeodomain Proteins MeSH
• PHB protein, Arabidopsis MeSH Browser
• Arabidopsis Proteins MeSH
• SCR protein, Arabidopsis MeSH Browser
• SHORT ROOT protein, Arabidopsis MeSH Browser
• Transcription Factors MeSH