Abstract
Plants sense and respond to light via multiple photoreceptors including phytochrome. The decreased ratio of red to far-red light that occurs under a canopy triggers shade-avoidance responses, which allow plants to compete with neighboring plants. The leaf acts as a photoperceptive organ in this response. In this study, we investigated how the shade stimulus is spatially processed within the cotyledon. We performed transcriptome analysis on microtissue samples collected from vascular and nonvascular regions of Arabidopsis (Arabidopsis thaliana) cotyledons. In addition, we mechanically isolated and analyzed the vascular tissue. More genes were up-regulated by the shade stimulus in vascular tissues than in mesophyll and epidermal tissues. The genes up-regulated in the vasculature were functionally divergent and included many auxin-responsive genes, suggesting that various physiological/developmental processes might be controlled by shade stimulus in the vasculature. We then investigated the spatial regulation of these genes in the vascular tissues. A small vascular region within a cotyledon was irradiated with far-red light, and the response was compared with that when the whole seedling was irradiated with far-red light. Most of the auxin-responsive genes were not fully induced by the local irradiation, suggesting that perception of the shade stimulus requires that a wider area be exposed to far-red light or that a certain position in the mesophyll and epidermis of the cotyledon be irradiated. This result was consistent with a previous report that auxin synthesis genes are up-regulated in the periphery of the cotyledon. Hence, auxin acts as an important intraorgan signaling factor that controls the vascular shade response within the cotyledon.
Highlights
Plants sense and respond to light via multiple photoreceptors including phytochrome
To investigate the spatial regulation of the gene expression responses to the shade stimulus within cotyledons, micro samples were prepared from two distinct regions of cotyledons of 4-d-old Arabidopsis seedlings using a needle-based device (Kajiyama et al, 2015; Nito et al, 2015; Fig. 1)
The MN sample of ∼100 μm in diameter was excised from a nonvascular region in the Downloaded from on October 5, 2020 - Published by www.plantphysiol.org Plant Physiol
Summary
Plants sense and respond to light via multiple photoreceptors including phytochrome. The decreased ratio of red to far-red light that occurs under a canopy triggers shade-avoidance responses, which allow plants to compete with neighboring plants. The genes up-regulated in the vasculature were functionally divergent and included many auxin-responsive genes, suggesting that various physiological/developmental processes might be controlled by shade stimulus in the vasculature. Most of the auxinresponsive genes were not fully induced by the local irradiation, suggesting that perception of the shade stimulus requires that a wider area be exposed to far-red light or that a certain position in the mesophyll and epidermis of the cotyledon be irradiated. This result was consistent with a previous report that auxin synthesis genes are up-regulated in the periphery of the cotyledon. The physiological consequence of auxin accumulation can vary depending on the organ (de Wit et al, 2015)
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