The primary signaling outputs of brassinosteroids are regulated by abscisic acid signaling

Abstract

Phytohormones have essential roles in coordinately regulating a large array of developmental processes. Studies have revealed that brassinosteroids (BRs) and abscisic acid (ABA) interact to regulate hundreds of expression in genes, governing many biological processes. However, whether their interaction is through modification or intersection of their primary signaling cascades, or by independent or parallel pathways remains a big mystery. Using biochemical and molecular markers of BR signaling and ABA biosynthetic mutants, we demonstrated that exogenous ABA rapidly inhibits BR signaling outputs as indicated by the phosphorylation status of BES1 and BR-responsive gene expression. Experiments using a bri1 null-allele, bri1-116, and analysis of subcellular localization of BKI1-YFP further revealed that the BR receptor complex is not required for ABA to act on BR signaling outputs. However, when the BR downstream signaling component BIN2 is inhibited by LiCl, ABA failed to inhibit BR signaling outputs. Also, using a set of ABA insensitive mutants, we found that regulation of ABA on the BR primary signaling pathway depends on the ABA early signaling components, ABI1 and ABI2. We propose that the signaling cascades of ABA and BR primarily cross-talk after BR perception, but before their transcriptional activation. This model provides a reasonable explanation for why a large proportion of BR-responsive genes are also regulated by ABA, and provides an insight into the molecular mechanisms by which BRs could interact with ABA.cross-talk ͉ gene expression ͉ phosphorylation ͉ seed germination ͉ signal transduction U nlike animals, plants are sessile and need to constantly regulate their developmental and physiological processes to respond to various internal and external stimuli. Studies have revealed that many biological processes result from integrating multiple hormonal signals, and extensive cross-talk among different hormonal signaling pathways is present in plants (1, 2). Recently, a large set of microarray data verified that many genes are coregulated by multiple hormones, suggesting the importance of hormones to coordinately regulate biological processes in plants (3,4). A few studies have also elucidated specific molecular mechanisms of hormonal cross-talk. They include the role of auxin and ethylene in regulating root meristem development (1), the antagonistic relationship between abscisic acid (ABA) and gibberellins (GAs) on seed dormancy and germination (5, 6), and integration of the primary signaling pathways of auxin and brassinosteroids (BRs) by auxin response factor 2 (ARF2) (7).Studies have indicated that BRs and ABA can coregulate the expression of hundreds of genes (4), and they interact physiologically in controlling many developmental processes (5,(8)(9)(10). It is also well known that ABA is required to establish seed dormancy during embryo maturation and to inhibit seed germination (5), whereas BRs promote seed germination, likely through enhancing the embryo growth potential to antagonize the effect...

Identification and characterization of the BZR transcription factor family and its expression in response to abiotic stresses in Zea mays L.

“…These apparently conflicting data might be explained considering that BRs perform diverse functions by sharing signaling pathways with other phytohormones. For example, it has been demonstrated that ABA inhibits plant growth by suppressing BR signaling downstream of BR receptor (Zhang et al 2009). An antagonistic interaction has been also evidenced between BRs and gibberellins, since the GA repressor DELLA directly interacts with BZR1 to inhibit its DNA binding and thus transcription activity in controlling photomorphogenesis (Sun et al 2010;Li et al 2012).…”

Control of early seedling development by BES1/TPL/HDA19-mediated epigenetic regulation of ABI3

“…There are multiple overlaps in the gene sets regulated by BR and GA, and in the biological effects of these two hormones, and the BR-regulated transcriptional activity of BZR1 and BES1 is known to be required for proper GA responses in skotomorphogenic seedlings 1,3 . In addition, similar to GAs, BRs play negative roles in ABA-inhibited early seedling development [14][15][16] , and exogenous BR application or overexpression of BR biosynthetic DWF4 can overcome the low seed germination phenotype of GAdefective mutants 43 . Furthermore, central negative regulators of GA signalling, DELLA proteins, could directly inhibit the transcriptional activity of BES1 and BZR1, and BR activity was required for GA-mediated cell elongation 1,3 .…”

“…Exogenous BR application rescued the low germination phenotype of GA-related mutants and BR-defective mutants are hypersensitive to ABA during early seedling development and stomatal closure [14][15][16] . Furthermore, the biologically active BR (brassinolide and castasterone) and BR biosynthetic gene expression were greatly increased during seed growth and germination of Pisum sativum (pea) 17 .…”

“…BR was reported to have antagonist effects on ABA signalling based on the findings that the BR-defective det2, bri1 and bin2-1 mutants are hypersensitive to ABA during early seedling development 14,22 . Furthermore, ABI2-mediated ABA signalling pathways were shown to negatively control primary BR signalling outputs by facilitating BIN2 activity 16 , suggesting that the coordination of BR and ABA signalling is accomplished by the BIN2-regulated transcriptional activity of BES1 or BZR1. However, the molecular mechanisms that integrate BR signalling pathways with ABA signalling in early seedling development are largely unknown.…”

Plant Stress Surveillance Monitored by ABA and Disease Signaling Interactions

“…In addition to the genetic interactions of ABA signaling with ethylene, gibberellins, and brassinosteroids signal transduction in embryonic and early postembryonic development (Beaudoin et al, 2000;Gazzarrini et al, 2004;Ghassemian et al, 2000;Zhang et al, 2009), novel roles of ABA signaling during pathogen infection and following defense responses against biotic stresses have been suggested (Asselbergh et al, 2008;Cao et al, 2011;Fujita et al, 2006;Ton et al, 2009). Jasmonic acid (JA) and salicylic acid (SA) are two major plant hormones regulating plant biotic stress signal transduction.…”