Abscisic acid modulates neighbor proximity-induced leaf hyponasty in Arabidopsis

Abstract

Leaves of shade-avoiding plants such as Arabidopsis (Arabidopsis thaliana) change their growth pattern and position in response to low red to far-red ratios (LRFRs) encountered in dense plant communities. Under LRFR, transcription factors of the phytochrome interacting factor (PIF) family are de-repressed. PIFs induce auxin production, which is required for promoting leaf hyponasty, thereby favoring access to unfiltered sunlight. Abscisic acid (ABA) has also been implicated in the control of leaf hyponasty, with gene expression patterns suggesting that LRFR regulates the ABA response. Here, we show that LRFR leads to a rapid increase in ABA levels in leaves. Changes in ABA levels depend on PIFs, which regulate the expression of genes encoding isoforms of the enzyme catalyzing a rate-limiting step in ABA biosynthesis. Interestingly, ABA biosynthesis and signaling mutants have more erect leaves than wild-type Arabidopsis under white light but respond less to LRFR. Consistent with this, ABA application decreases leaf angle under white light; however, this response is inhibited under LRFR. Tissue-specific interference with ABA signaling indicates that an ABA response is required in different cell types for LRFR-induced hyponasty. Collectively, our data indicate that LRFR triggers rapid PIF-mediated ABA production. ABA plays a different role in controlling hyponasty under white light than under LRFR. Moreover, ABA exerts its activity in multiple cell types to control leaf position.

A transcriptome atlas ofStriga hermonthicagermination

“…One possibility is that Striga maintains hyperactive phytochromes consistent with the phenotypes of PHYA over-expressors (FRANKLIN and WHITELAM, 2005). Interestingly, it was recently shown that ABA modulates shade avoidance by inducing hyponasty movement in Arabidopsis (Michaud et al, 2022) adding to another piece of circumstantial evidence for ABA involvement in Striga ’s germination and infection process. This is an interesting subject for future investigation.…”

Waterlogging shifts ontogenic hormone dynamics in tomato leaves and petioles

“…Next, auxin signaling in the lower side of the petiole stimulates local gibberellic acid (GA) biosynthesis, initiating abaxial cell elongation, and hence petiole hyponasty (Küpers et al, 2022). Concomitantly, abscisic acid (ABA) signaling stimulates hyponasty, potentially through the interaction with sugar signaling (Michaud et al, 2022). Much of the SAS-related hormonal crosstalk is shared with thermonastic responses.…”

Let the sunshine in: Abscisic acid modulates shade avoidance by inducing hyponasty movement in Arabidopsis

“…Although the pivotal function of auxin in regulating LRFR-induced hyponasty has been well-studied (Michaud et al, 2017;Pantazopoulou et al, 2017), knowledge on the role of other phytohormones in this phenomenon is scarce. In this issue of Plant Physiology, Michaud et al (2022) report that abscisic acid (ABA) plays a crucial role in mediating LRFR-induced hyponasty. They demonstrate that exposure to LRFR rapidly increases the biosynthesis of ABA, which is necessary for the upward movement of leaves in the proximity of competing neighbors.…”

“…LRFR induces auxin production in the leaf blade, which ultimately mediates the hyponastic leaf movement (Michaud et al, 2017). Considering this, Michaud et al (2022) compared leaf movements of WT and aba2 after exogenous application of auxin (Indole-3-acetic acid, IAA) to their leaf tips. The aba2 mutant exhibited a reduced hyponastic response compared to WT upon IAA application, indicating that auxin-induced leaf movements require ABA biosynthesis.…”

“…Historically, with few exceptions, elongation of hypocotyls and petioles have been used as the primary readout for studying the mechanisms of shade avoidance (Ballare ´and Pierik, 2017). The findings from Michaud et al (2022) substantially add to our understanding of the mechanism of altered leaf movements, which is an equally important attribute under foliar shade. Accumulating evidence emphasizes the importance of the interactions between light and ABA signaling pathways in multiple aspects of plant development (Yadukrishnan and Datta, 2021).…”