Abstract
Size control is a fundamental question in biology, showing incremental complexity in plants, whose cells possess a rigid cell wall. The phytohormone auxin is a vital growth regulator with central importance for differential growth control. Our results indicate that auxin-reliant growth programs affect the molecular complexity of xyloglucans, the major type of cell wall hemicellulose in eudicots. Auxin-dependent induction and repression of growth coincide with reduced and enhanced molecular complexity of xyloglucans, respectively. In agreement with a proposed function in growth control, genetic interference with xyloglucan side decorations distinctly modulates auxin-dependent differential growth rates. Our work proposes that auxin-dependent growth programs have a spatially defined effect on xyloglucan’s molecular structure, which in turn affects cell wall mechanics and specifies differential, gravitropic hypocotyl growth.
Highlights
The phytohormone auxin is a central regulator of plant development and is of pivotal importance for differential growth control
Biochemical and imaging approaches, we provide evidence that auxin-dependent growth programs exert a spatial control on XyG structure, namely on the level and types of backbone substitutions, which contributes to gravity induced, differential growth in dark grown hypocotyls
In order to study auxin-reliant differential growth, we exposed plants to a gravitropic stimulus, which activates a complex sequence of events inducing an asymmetric increase of auxin and cellular elongation at the lower side of the shoot [31]
Summary
The phytohormone auxin is a central regulator of plant development and is of pivotal importance for differential growth control. We do not fully understand the subcellular mechanisms by which auxin reliant growth programs define the size of a cell that is surrounded by a rigid cell wall structure. Auxin signaling steers promotion and repression of cell expansion in a concentration- and cell-type-dependent manner [1]. Tissue specific expression of auxin signaling components and intracellular auxin transport define cellular sensitivity to auxins [5,6,7]. Transcriptional auxin responses take place in the nucleus via auxin binding to its co-receptors transport inhibitor response 1/auxin signaling F-box (TIR1/AFBs) and the transcriptional repressor auxin/indole-3-acetic acid (Aux/IAAs) [8]. Auxin-induced cellular elongation in hypocotyls requires TIR1/AFBs-dependent transcriptional auxin responses [9]. Auxin-triggered repression of root cell expansion utilizes a TIR1/AFBs-dependent, non-genomic pathway [10].
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