PLETHORA gradient formation mechanism separates auxin responses

• Published in: Nature (London) Vol. 515; no. 7525; pp. 125 - 129
• Main Authors: Mähönen, Ari Pekka, Tusscher, Kirsten ten, Siligato, Riccardo, Smetana, Ondřej, Díaz-Triviño, Sara, Salojärvi, Jarkko, Wachsman, Guy, Prasad, Kalika, Heidstra, Renze, Scheres, Ben
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 06.11.2014; Nature Publishing Group
• Subjects: 13/100; 13/89; 14/19; 14/35; 14/63; 38/39; 42/44; 45; 45/22; 45/23; 631/114/2397; 631/449/1741/1576; 631/449/1975; 631/449/2653/1974; angiogenesis; Arabidopsis - cytology; Arabidopsis - growth & development; Arabidopsis - metabolism; Arabidopsis Proteins - metabolism; arabidopsis root apex; Arabidopsis thaliana; carcinoma cells; Cell Differentiation; Cell division; Cell growth; Cell Movement; Cloning; Environmental conditions; expression; Gene Expression Regulation, Plant; genomics browser; Gravitropism; Humanities and Social Sciences; Indoleacetic Acids - metabolism; inflammatory breast-cancer; letter; Meristem - growth & development; Meristem - metabolism; Mitosis; monocyte chemoattractant protein-1; multidisciplinary; Plant growth; Plant Roots - cytology; Plant Roots - growth & development; Plant Roots - metabolism; Proteins; Science; Stem cells; stem-cell niche; Studies; Transcription factors; Transcription Factors - metabolism; tumor; Zonation
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature13663

Through a combination of experimental and computational approaches, the interplay between the plant hormone auxin and the auxin-induced PLETHORA transcription factors is shown to control zonation and gravity-prompted growth movements in plants. Auxin responses versus plant growth Gradients of the plant hormone auxin and of auxin-induced PLETHORA (PLT) transcription factors control plant division into distinct developmental zones. Auxin is also essential for the tropic responses through which plants rapidly adjust their direction of growth to adapt to environmental conditions. Using a combination of experimental and computational approaches, Ari Pekka Mähönen et al . show how an interplay of auxin and PLTs controls zonation and gravitropism. They find that PLT gradient is not a direct readout of the auxin gradient. Instead, prolonged high auxin levels generate a narrow PLT transcription domain from which a PLT gradient is generated, defining the location of developmental zones. This specific regulatory design in which auxin cooperates with PLTs through different mechanisms and on different timescales allows both fast tropic environmental responses and stable zonation dynamics necessary for coordinated cell differentiation. During plant growth, dividing cells in meristems must coordinate transitions from division to expansion and differentiation, thus generating three distinct developmental zones: the meristem, elongation zone and differentiation zone 1 . Simultaneously, plants display tropisms, rapid adjustments of their direction of growth to adapt to environmental conditions. It is unclear how stable zonation is maintained during transient adjustments in growth direction. In Arabidopsis roots, many aspects of zonation are controlled by the phytohormone auxin and auxin-induced PLETHORA (PLT) transcription factors, both of which display a graded distribution with a maximum near the root tip 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 . In addition, auxin is also pivotal for tropic responses 13 , 14 . Here, using an iterative experimental and computational approach, we show how an interplay between auxin and PLTs controls zonation and gravitropism. We find that the PLT gradient is not a direct, proportionate readout of the auxin gradient. Rather, prolonged high auxin levels generate a narrow PLT transcription domain from which a gradient of PLT protein is subsequently generated through slow growth dilution and cell-to-cell movement. The resulting PLT levels define the location of developmental zones. In addition to slowly promoting PLT transcription, auxin also rapidly influences division, expansion and differentiation rates. We demonstrate how this specific regulatory design in which auxin cooperates with PLTs through different mechanisms and on different timescales enables both the fast tropic environmental responses and stable zonation dynamics necessary for coordinated cell differentiation.