Environmental Control of Hypocotyl Elongation

Abstract

The hypocotyl is the embryonic stem connecting the primary root to the cotyledons. Hypocotyl length varies tremendously depending on the conditions. This developmental plasticity and the simplicity of the organ explain its success as a model for growth regulation. Light and temperature are prominent growth-controlling cues, using shared signaling elements. Mechanisms controlling hypocotyl elongation in etiolated seedlings reaching the light differ from those in photoautotrophic seedlings. However, many common growth regulators intervene in both situations. Multiple photoreceptors including phytochromes, which also respond to temperature, control the activity of several transcription factors, thereby eliciting rapid transcriptional reprogramming. Hypocotyl growth often depends on sensing in green tissues and interorgan communication comprising auxin. Hypocotyl auxin, in conjunction with other hormones, determines epidermal cell elongation. Plants facing cues with opposite effects on growth control hypocotyl elongation through intricate mechanisms. We discuss the status of the field and end by highlighting open questions. Expected final online publication date for the Annual Review of Plant Biology, Volume 75 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The ELF3-BBX24/BBX25-PIF4 module controls thermosensory growth in Arabidopsis

“…Warm temperature-mediated hypocotyl growth is linked to enhanced accumulation of auxin, brassinosteroid (BR) and gibberellic acid (GA) growth hormones, which is largely mediated by PIF4 and BZR1 (Gray et al, 1998; Stavang et al, 2009; Franklin et al, 2011; Oh et al, 2012; Ibanez et al, 2018; Krahmer and Fankhauser, 2023). As BBX24/BBX25 act to promote PIF4 function, we wanted to see if BBX24/BBX25 are involved in inducing growth hormone accumulation.…”

“…Ecological cues such as light and temperature are key in regulating plant growth, architecture, and fitness (Franklin et al, 2014; Casal and Questa, 2018; Casal and Balasubramanian, 2019; Legris et al, 2019; Lippmann et al, 2019; Quint et al, 2023). Plants have evolved sophisticated and multifaceted mechanisms to perceive, integrate, and process these cues (Legris et al, 2019; Krahmer and Fankhauser, 2023). Because plants experience these conflicting signals in nature, they must constantly sense and integrate these signals to optimise growth and acclimatise to the local environments.…”

“…Temperature has a multitude of effects on plant development (Casal and Balasubramanian, 2019; Quint et al, 2023). Specifically, warm ambient temperatures strongly influence plant growth by accelerating vegetative and reproductive transitions, resulting in shortened life-cycle duration (Koini et al, 2009; Crawford et al, 2012; Kumar et al, 2012; Casal and Balasubramanian, 2019; Krahmer and Fankhauser, 2023; Quint et al, 2023). However, warm temperatures strongly compromise immunity and also severely affect seed set and yield (Koester et al, 2014; Zhao et al, 2017; Burroughs et al, 2023).…”

“…PIF4 is essential for warm temperature-induced hypocotyl and petiole growth, rosette development, hyponasty, and flowering (Koini et al, 2009; Kumar et al, 2012; Oh et al, 2012; Quint et al, 2016; Casal and Balasubramanian, 2019; Favero et al, 2020; Zhao and Bao, 2021; Quint et al, 2023). PIF4-mediated thermomorphogeneis is linked to the activation of genes involved in auxin/brassinosteroid biosynthesis and signaling (Franklin et al, 2011; Sun et al, 2012; Ibanez et al, 2018; Krahmer and Fankhauser, 2023), cell elongation (Gangappa and Kumar, 2017) and flowering (Kumar et al, 2012). Warm temperature-mediated inhibition of phyB activity increases PIF4 activity, resulting in the thermosensory growth (Legris et al, 2016).…”

An active light signalling pathway is necessary for ABA-induced inhibition of hypocotyl elongation

“…In nature, for some species, hypocotyl elongation, at early stages of seed development, represents the capacity to emerge from soil and perceive light ensuring the establishment as autotrophic self-sustained organism. Once this establishment occurs, at the initial developmental stages, hypocotyl elongation is crucial for early plant responsiveness to environmental light conditions as light cues, temperature, hypoxia or drought (Boron and Vissenberg, 2014;Krahmer and Fankhauser, 2023).…”