Abstract
Plant uses multiple photoreceptors and downstream components to rapidly respond to dynamic changes in environmental light. Under shade conditions, many species exhibit shade avoidance responses that promote stem and petiole elongation, thus helping plants reach the sunlight. In the last few years, the regulatory molecular mechanisms by which plants respond to shade signals have been intensively studied. This review discusses the regulatory mechanisms underlying auxin-mediated cell elongation in the shade avoidance responses. In the early response to shade signals, auxin biosynthesis, transport, and sensitivity are all rapidly activated, thus promoting cell elongation of the hypocotyls and other organs. Under prolonged shade, increased auxin sensitivity—rather than increased auxin biosynthesis—plays a major role in cell elongation. In addition, we discuss the interaction network of photoreceptors and Phytochrome-Interacting Factors, and the antagonistic regulation of Auxin/Indole Acetic Acid proteins by auxin and light. This review provides perspectives to reframe how we think about shade responses in the natural environment.
Highlights
Light is a vital resource for green plants, as it provides an energy source for photosynthesis and acts as a signal to direct plant growth and development
We focus on the current understanding of auxin-mediated cell elongation under various shade conditions in Arabidopsis thaliana
This indicates that polar auxin transport from the cotyledon to the hypocotyl is required for the shade avoidance response (Keuskamp et al, 2010; Kohnen et al, 2016)
Summary
Light is a vital resource for green plants, as it provides an energy source for photosynthesis and acts as a signal to direct plant growth and development. In leaves at the top of the canopy, chlorophylls and other pigments absorb blue (400–500 nm, B) and red (600–700 nm; R) wavelengths of light. Most shade-intolerant species (e.g., Arabidopsis thaliana) exhibit shade avoidance responses, including enhanced cell elongation in various organs (hypocotyl, petioles, internode, stem, and branches), increased hyponastic growth of leaves, and accelerated flowering time (Franklin, 2008; Casal, 2012, 2013). When growing taller is not an option, some plants exhibit a series of tolerance-related morphological and physiological changes, including expanded leaf size and area, decreased leaf thickness, and reduced chlorophyll a:b ratio, increasing plant performance and the efficiency of light capture under shade and dim-light conditions (Gommers et al, 2013). We focus on the current understanding of auxin-mediated cell elongation under various shade conditions in Arabidopsis thaliana
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