BBX24 Interacts with JAZ3 to Promote Growth by Reducing DELLA Activity in Shade Avoidance

Abstract

Shade avoidance syndrome (SAS) is a strategy of major adaptive significance and typically includes elongation of the stem and petioles, leaf hyponasty, reduced branching, and phototropic orientation of the plant shoot toward canopy gaps. Cryptochrome 1 and phytochrome B (phyB) are both the major photoreceptors that sense the reduction in blue light fluence rate and the low Red:Far-Red (R:FR) ratio, respectively, both light signals associated with plant density and the resource reallocation when SAS responses are triggered. BBX24 has been implicated in the SAS as a regulator of DELLA activity, but this interaction does not explain all the observed BBX24-dependent regulation in shade light. Here, through a combination of transcriptional meta-analysis and large-scale identification of BBX24-interacting transcription factors, we found that JAZ3, a jasmonic acid signaling component, is a direct target of BBX24. Furthermore, we demonstrated that joint loss of BBX24 and JAZ3 function causes insensitivity to DELLA accumulation, and the defective shade-induced elongation in this mutant is rescued by loss of DELLA or phytochrome B functions. Therefore, we propose that JAZ3 is part of the regulatory network that controls the plant growth in response to shade, through a mechanism in which BBX24 and JAZ3 jointly regulate DELLA activity. Our results provide new insights into the participation of BBX24 and JA signaling in the hypocotyl shade avoidance response in Arabidopsis.

BBX24 Increases Saline and Osmotic Tolerance through ABA Signaling in Arabidopsis Seeds

“…The negative interaction between BBX24 and HY5, and its closest homolog HYH, is a common theme in the regulation of seedling photomorphogenesis [17][18][19]22]. In simulated shade, BBX24 can sequester DELLA to promote elongation responses through PIF4 activity [23,24]. More recently, it has been suggested that the module of HY5-BBX24-DELLA can control the crosstalk between GA and UV-B signaling to regulate hypocotyl inhibition [21].…”

“…Several BBX proteins have been documented to be involved in seedling de-etiolation, synthesis of anthocyanins, shade avoidance, flowering and responses to abiotic and biotic stresses [13,16]. BBX24 has been documented to inhibit seedling deetiolation [17][18][19][20], repress UVB signaling [21,22] and promote shade avoidance [17,23,24] and flowering [25]. BBX24 was originally isolated as a SALT-TOLERANT (STO) protein in an Arabidopsis cDNA clone screen that conferred increased salt-tolerance in Saccharomyces cerevisiae [26,27].…”

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

“…The BBX24 and BBX25 are close homologs that function as transcriptional co-repressors of HY5 to inhibit photomorphogenesis (Gangappa et al, 2013; Job et al, 2018). Additionally, BBX24 functions in various signaling pathways, including UV-B signaling (Jiang et al, 2012; Huang et al, 2022), shade-avoidance response (Crocco et al, 2015b; Saura-Sanchez et al, 2023) and flowering (Li et al, 2014). However, the role of BBX24 and BBX25 in temperature-mediated regulation of growth and development remains unknown.…”