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Root system architecture from coupling cell shape to auxin transport.

ABSTRACT: Lateral organ position along roots and shoots largely determines plant architecture, and depends on auxin distribution patterns. Determination of the underlying patterning mechanisms has hitherto been complicated because they operate during growth and division. Here, we show by experiments and computational modeling that curvature of the Arabidopsis root influences cell sizes, which, together with tissue properties that determine auxin transport, induces higher auxin levels in the pericycle cells on the outside of the curve. The abundance and position of the auxin transporters restricts this response to the zone competent for lateral root formation. The auxin import facilitator, AUX1, is up-regulated by auxin, resulting in additional local auxin import, thus creating a new auxin maximum that triggers organ formation. Longitudinal spacing of lateral roots is modulated by PIN proteins that promote auxin efflux, and pin2,3,7 triple mutants show impaired lateral inhibition. Thus, lateral root patterning combines a trigger, such as cell size difference due to bending, with a self-organizing system that mediates alterations in auxin transport.

SUBMITTER: Laskowski M

PROVIDER: S-EPMC2602721 | biostudies-literature | 2008 Dec

REPOSITORIES: biostudies-literature

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Root system architecture from coupling cell shape to auxin transport.

Laskowski Marta M Grieneisen Verônica A VA Hofhuis Hugo H Hove Colette A Ten CA Hogeweg Paulien P Marée Athanasius F M AF Scheres Ben B

PLoS biology 20081201 12

Lateral organ position along roots and shoots largely determines plant architecture, and depends on auxin distribution patterns. Determination of the underlying patterning mechanisms has hitherto been complicated because they operate during growth and division. Here, we show by experiments and computational modeling that curvature of the Arabidopsis root influences cell sizes, which, together with tissue properties that determine auxin transport, induces higher auxin levels in the pericycle cell ...[more]

PMID: 19090618

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Project description:Azospirillum is a plant growth promoting rhizobacteria (PGPR) with ability to produce several phytohormones such as auxins, mainly indole-3-acetic acid (IAA). The positive interaction of Azospirillum with plants has been simplified and explained through the bacterial capacity to produce IAA. Typical changes on root architecture by promoting the number of lateral roots and hair formation, and reducing the primary root length were established in inoculated plants. These changes increase the root surface improving the water and nutrients acquisition, and thus the growth of the whole plant. The mechanisms by which Azospirillum induces such changes fails to be explained only by the bacterial capacity to produce IAA. In this work, we have evaluated the root architecture and gene expression changes occurred in Arabidopsis thaliana inoculated with A. brasilense Az39 and the IAA-deficient mutant (Az39 ipdC-), or treated with exogenous IAA solution to confirm both, the IAA-dependent and IAA-independent Azospirillum´s pathways to promote the root growth. Our results demonstrate the ability of Az39 to modify the primary root development through IAA biosynthesis, while other IAA-independent mechanisms were related to an increase in the lateral roots development and the root hairs number. Jasmonates, ethylene and salicylic acid were increased in the IAA-deficient bacterial treatments, as the ipdC mutant significantly up-regulated transcription of genes enriched of these phytohormones signaling after 7 days. Further, the physical presence of the inactive bacteria (Az39φ) seems to mediate the development of root hairs, a mechanism common to other non-PGPR as E. coli DH5α. Our results suggest that Az39 inoculation induces morphological changes in root architecture through both IAA-dependent and independent mechanism. The IAA biosynthesis by Az39 reduces the primary root length; while the cells contact with the roots increases the root hairs production. Both the synthesis of active IAA and the presence of metabolically active Az39 cells increase the growth and development of lateral roots.

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Root system architecture from coupling cell shape to auxin transport.

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Root system architecture from coupling cell shape to auxin transport.

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