Plant Science

Root Growth Revealed

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Science  23 Dec 2011:
Vol. 334, Issue 6063, pp. 1607
DOI: 10.1126/science.334.6063.1607-b

In the growing Arabidopsis root tip, the hormone auxin regulates cell division and differentiation from the stem cell niche. Auxin is expressed as a gradient, which peaks at the root meristem, where stem cells drive root growth. This asymmetry is maintained by transporter proteins that are themselves asymmetrically organized to transport auxin from cell to cell. The gene BREVIS RADIX (BRX), which is regulated by auxin, does not, however, function in a pattern that reflects the auxin distribution. Through a combination of experiment and dynamic computational modeling to describe the interactions of hormone and targets, Santuari et al. found out why. The BRX gene appeared to encode a transcriptional coregulator despite BRX primarily localizing to the plasma membrane. Because BRX function in the nucleus is dependent on endocytic recycling, the authors layered endocytosis pathways into their computational model. The endocytic pathways themselves respond to auxin, although in a nonlinear manner. By combining the various inputs, the authors generated a model that reflected BRX function in the normal root. Thus, although auxin regulates BRX transcription, the association of BRX with the plasma membrane, and the activity of the endocytic pathways required to get BRX to the nucleus, add up to a cellular distribution of BRX that does not parallel the distribution of auxin.

Curr. Biol. 21, 1918 (2011).

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