Abstract
Plants are highly attuned to translating environmental changes to appropriate modifications in growth. Such phenotypic plasticity is observed in dense vegetations, where shading by neighboring plants, triggers rapid unidirectional shoot growth (shade avoidance), such as petiole elongation, which is partly under the control of auxin. This growth is fuelled by cellular expansion requiring cell-wall modification by proteins such as xyloglucan endotransglucosylase/hydrolases (XTHs). Cortical microtubules (cMTs) are highly dynamic cytoskeletal structures that are also implicated in growth regulation. The objective of this study was to investigate the tripartite interaction between auxin, cMTs and XTHs in shade avoidance. Our results indicate a role for cMTs to control rapid petiole elongation in Arabidopsis during shade avoidance. Genetic and pharmacological perturbation of cMTs obliterated shade-induced growth and led to a reduction in XTH activity as well. Furthermore, the cMT disruption repressed the shade-induced expression of a specific set of XTHs. These XTHs were also regulated by the hormone auxin, an important regulator of plant developmental plasticity and also of several shade avoidance responses. Accordingly, the effect of cMT disruption on the shade enhanced XTH expression could be rescued by auxin application. Based on the results we hypothesize that cMTs can mediate petiole elongation during shade avoidance by regulating the expression of cell wall modifying proteins via control of auxin distribution.
Highlights
The ‘shade avoidance syndrome’ (SAS), induced by aboveground plant-plant competition represents a classic example of successful adaptive environmental sensing and response [1,2]
Considering the important role of auxin and polar auxin transport in mediating shade avoidance responses, we investigated the role of Cortical microtubules (cMTs) in mediating shade-induced petiole elongation in Arabidopsis via regulation of auxin transport
In order to determine the effect of cMT disruption on shade avoidance, plants were treated with the cMT disrupting drug oryzalin
Summary
The ‘shade avoidance syndrome’ (SAS), induced by aboveground plant-plant competition represents a classic example of successful adaptive environmental sensing and response [1,2]. When canopy closure occurs, shaded plants experience a simultaneous occurrence of both low R:FR and low blue These reductions in blue light and R:FR are important cues that are sensed by the plant photoreceptors as a shading threat [3,4,5] and initiates a suite of morphological responses that constitutes the SAS. Cellular expansion occurs when cell walls yield to turgor pressure within the cell resulting in a relaxation of wall stress This ‘cell-wall loosening’ is the result of proteins that modify cell-wall structure [7,8]. Upstream of the expansins and XTHs are various components regulating SAS Amongst these is the phytohormone auxin, which is an important regulator of shade-induced growth responses in plants [13]. In Arabidopsis seedlings exposed to low R:FR, the auxin transporter protein PIN-FORMED3 (PIN3) changes from a basal to lateral distribution driving auxin towards the cortical and epidermal cells where cellular expansion occurs [19]
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