Abstract
When subject to vegetational shading, shade-avoiding plants detect neighbors by perceiving reduced light quantity and altered light quality. The former includes decreases in the ratio of red to far-red wavelengths (low R:FR) and low blue light ratio (LBL) predominantly detected by phytochromes and cryptochromes, respectively. By integrating multiple signals, plants generate a suite of responses, such as elongation of a variety of organs, accelerated flowering, and reduced branching, which are collectively termed the shade-avoidance syndrome (SAS). To trigger the SAS, interactions between photoreceptors and phytochrome-interacting factors are the general switch for activation of downstream signaling pathways. A number of transcription factor families and phytohormones, especially auxin, gibberellins, ethylene, and brassinosteroids, are involved in the SAS processes. In this review, shade signals, the major photoreceptors involved, and the phenotypic characteristics of the shade-intolerant plant Arabidopsis thaliana are described in detail. In addition, integration of the signaling mechanisms that link photoreceptors with multiple hormone signaling pathways is presented and future research directions are discussed.
Highlights
Sunlight is the energy source for plant growth
Recruited by PIF7, ARABIDOPSIS MORF RELATED GENE 1 (MRG1) and MRG2 were combined with H3K4me3/H3K36me3 to induce histone acetylation and, in this manner, the two genes promote the expression of shaderesponsive genes, which include YUCCA8 and IAA19 that participate in the biosynthesis and signaling pathways of auxin, and PACLOBUTRAZOL RESISTANCE1/BANQUO1 (PRE1/ BNQ1), which is involved in brassinosteroid-regulated cell elongation (Peng et al, 2018)
The above findings robustly indicate that multiple photoreceptors as well as several central circadian components connect immediately to downstream transcriptional networks through direct binding to, and repression of, the members of phytochrome-interacting factors (PIFs) quintet (PIF1, PIF3, PHYTOCHROME INTERACTING FACTOR 4 (PIF4), PIF5, and PIF7) that comprise the signaling hub (Franklin, 2020; Zhang et al, 2020)
Summary
Sunlight is the energy source for plant growth. The spectrum of solar radiation utilized by green plants for conducting photosynthesis is termed photosynthetically active radiation (PAR; 400–700 nm). Shade-avoidance responses involve a cascade reaction of the light signal system, plant hormone signaling pathways, and growth regulation (Smith and Whitelam, 1997; Yang and Li, 2017).
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