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Root branching toward water involves posttranslational modification of transcription factor ARF7

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Science  21 Dec 2018:
Vol. 362, Issue 6421, pp. 1407-1410
DOI: 10.1126/science.aau3956

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Rooting out the mechanism of asymmetry

Plant roots grow not in response to architectural blueprints but rather in search of scarce resources in the soil. Orosa-Puente et al. show why a new lateral root emerges on the damp side of a root rather than the dry side (see the Perspective by Giehl and von Wirén). The transcription factor ARF7 is found across the whole root but acquires a posttranslational modification on the dry side of the root, which represses its function. ARF7 on the damp side remains functional and is thus able to initiate the signaling cascade that leads to a new lateral root.

Science, this issue p. 1407; see also p. 1358

Abstract

Plants adapt to heterogeneous soil conditions by altering their root architecture. For example, roots branch when in contact with water by using the hydropatterning response. We report that hydropatterning is dependent on auxin response factor ARF7. This transcription factor induces asymmetric expression of its target gene LBD16 in lateral root founder cells. This differential expression pattern is regulated by posttranslational modification of ARF7 with the small ubiquitin-like modifier (SUMO) protein. SUMOylation negatively regulates ARF7 DNA binding activity. ARF7 SUMOylation is required to recruit the Aux/IAA (indole-3-acetic acid) repressor protein IAA3. Blocking ARF7 SUMOylation disrupts IAA3 recruitment and hydropatterning. We conclude that SUMO-dependent regulation of auxin response controls root branching pattern in response to water availability.

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