Photoexcited CRY1 and phyB interact directly with ARF6 and ARF8 to regulate their DNA‐binding activity and auxin‐induced hypocotyl elongation in Arabidopsis

Abstract

Summary Arabidopsis CRY1 and phyB are the primary blue and red light photoreceptors mediating blue and red light inhibition of hypocotyl elongation, respectively. Auxin is a pivotal phytohormone involved in promoting hypocotyl elongation. CRY1 and phyB interact with and stabilize auxin/indole acetic acid proteins (Aux/IAAs) to inhibit auxin signaling. The present study investigated whether photoreceptors might interact directly with Auxin Response Factors (ARFs) to regulate auxin signaling. Protein–protein interaction studies demonstrated that CRY1 and phyB interact physically with ARF6 and ARF8 through their N‐terminal domains in a blue and red light‐dependent manner, respectively. Moreover, the N‐terminal DNA‐binding domain of ARF6 and ARF8 is involved in mediating their interactions with CRY1. Genetic studies showed that ARF6 and ARF8 act partially downstream from CRY1 and PHYB to regulate hypocotyl elongation under blue and red light, respectively. Chromatin immunoprecipitation‐PCR assays demonstrated that CRY1 and phyB mediate blue and red light repression of the DNA‐binding activity of ARF6 and ARF6‐target gene expression, respectively. Altogether, the results herein suggest that the direct repression of auxin‐responsive gene expression mediated by the interactions of CRY1 and phyB with ARFs constitutes a new layer of the regulatory mechanisms by which light inhibits auxin‐induced hypocotyl elongation.

Photoreceptors Regulate Plant Developmental Plasticity through Auxin

“…In the absence of IAA, AUX/IAAs inhibit auxin signalling by interacting with Auxin Response Factors (ARFs), preventing their DNA binding and transcriptional activity. ARF activity is further reduced by photoreceptor stabilisation of AUX/IAAs, and the formation of a transcriptionally inactive photoreceptor-AUX/IAA-ARF complex [29][30][31]. PhyB inactivation in persistent shade enhances auxin signalling through reduced expression of the TIR1-targeting miR393 [32].…”

“…This releases AUX/IAA repression of auxin related gene expression and cell growth [28]. Recent studies have established that photoreceptor activation by light prevents AUX/IAA degradation and thereby lessens the auxin induced growth response [29][30][31].…”

A point‐to‐point protein–protein interaction assay reveals the signaling interplays among plant hormones and environmental cues

“…CRY1, the homologue of CRY2, interacted with IAA7, IAA12, IAA17, ARF6, and ARF8 and mediated the light-auxin signaling-induced antagonistic regulation of hypocotyl elongation in recent studies (Mao et al, 2020;Xu et al, 2018). These PPIs confirm that auxin and light co-regulate plant development.…”

“…Auxin helps plants properly respond to light (Mao et al, 2020;Xu et al, 2018). In our screen, many IAA proteins were identified to interact with CRY2, a core component of the light signaling pathway (Table 1).…”

In Arabidopsis, low blue light enhances phototropism by releasing cryptochrome 1-mediated inhibition ofPIF4expression

“…Phenotypical experiments of seedlings defective for another class of blue light photoreceptors, called cryptochromes (cry), revealed that they modulate phototropism with a positive role in etiolated seedlings (Whippo and Hangarter, 2003; Ohgishi et al, 2004; Tsuchida-Mayama et al, 2010), and a potentially negative role in de-etiolated seedlings (Goyal et al, 2016). The Arabidopsis genome encodes two crys, cry1 and cry2, which coordinate blue light-mediated gene expression by the inactivation of the COP1/SPA E3 ligase complex (Holtkotte et al, 2017; Lau et al, 2019; Ponnu et al, 2019) or through the interaction with several transcription factors (Liu et al, 2008; Ma et al, 2016; Pedmale et al, 2016; Wang et al, 2018; Xu et al, 2018; He et al, 2019; Mao et al, 2020). Light-induced activation of cry1 and cry2 is controlled by BIC1 (Blue light Inhibitor of Cryptochrome 1) and BIC2 (Wang et al, 2016).…”