Light-Mediated Hormonal Regulation of Plant Growth and Development

Abstract

Light is crucial for plant life, and perception of the light environment dictates plant growth, morphology, and developmental changes. Such adjustments in growth and development in response to light conditions are often established through changes in hormone levels and signaling. This review discusses examples of light-regulated processes throughout a plant's life cycle for which it is known how light signals lead to hormonal regulation. Light acts as an important developmental switch in germination, photomorphogenesis, and transition to flowering, and light cues are essential to ensure light capture through architectural changes during phototropism and the shade avoidance response. In describing well-established links between light perception and hormonal changes, we aim to give insight into the mechanisms that enable plants to thrive in variable light environments.

Seedling Establishment: A Dimmer Switch-Regulated Process between Dark and Light Signaling

“…During the heterotrophic phase in darkness, PIF1 and PIF3 are negative regulators of chloroplast development, particularly of tetrapyrrole biosynthesis genes (Huq et al, 2004;Stephenson et al, 2009), and transcriptionally suppress together with EIN3 (which is stabilized by soil pressure-enhanced ET production; see Box 2; Lau and Deng, 2010;Leivar and Monte, 2014;de Lucas and Prat, 2014;Chaiwanon et al, 2016;de Wit et al, 2016a;Hornitschek et al, 2012;Pfeiffer et al, 2014;Zádníková et al, 2016;Li et al, 1996;Symons et al, 2002;Oh et al, 2012;Shahnejat-Bushehri et al, 2016;Li and He, 2016;Feng et al, 2008;de Lucas et al, 2008;Guzman and Ecker, 1990;Zhong et al, 2012;Jeong et al, 2016;Shi et al, 2016;Dong et al, 2017) chloroplast development genes . Among these are the transcription factors GOLDEN2-LIKE1 (GLK1) and GLK2, which are necessary for chloroplast development (Fitter et al, 2002;Oh and Montgomery, 2014), and target genes involved in chlorophyll biosynthesis, light harvesting, and electron transport (Waters et al, 2009).…”

“…To facilitate cell expansion, the cell wall of the epidermal cells gains flexibility, which appears to be independent of cell wall synthesis, and is regulated by specialized proteins such as expansins and XYLOGLUCAN ENDO-TRANSGLUCOSYLASE /HYDROLASEs (XTHs; Ivakov et al, 2017). In dark conditions, PIFs directly induce the expression of the genes encoding for these proteins (Leivar et al, 2009), and integrate the strong influence of several hormones such as auxin, brassinosteroids (BRs), GA, and ET in hypocotyl elongation (Box 2; for review, see Leivar and Monte, 2014;de Wit et al, 2016a; Fig. 3C).…”

Systemic induction of photosynthesis via illumination of the shoot apex is mediated by phytochrome B

“…Phytochrome signaling mediates many systemic responses in plants, including flowering time, tuberization, and nodule development, processes that are regulated by light-induced changes in phytohormone homeostasis (de Wit et al, 2016). Like PAT, the lightinduced signaling pathway that influences photosynthetic induction is basipetal.…”

Reciprocal proteasome-mediated degradation of PIFs and HFR1 underlies photomorphogenic development in Arabidopsis

“…By contrast, they undergo photomorphogenic development under light, which is characterized by short hypocotyl and expanded open cotyledons. Under red/far-red light conditions, photomorphogenesis is regulated by the phytochrome ( phy) family photoreceptors (Bae and Choi, 2008;de Wit, et al, 2016). Encoded by a small five-member family ( phyA-phyE) in Arabidopsis, phys can form homo-and heterodimers in vivo (Clack, et al, 2009).…”