Crosstalk of the Brassinosteroid Signalosome with Phytohormonal and Stress Signaling Components Maintains a Balance between the Processes of Growth and Stress Tolerance

Abstract

Brassinosteroids (BRs) are a class of phytohormones, which regulate various processes during plant life cycle. Intensive studies conducted with genetic, physiological and molecular approaches allowed identification of various components participating in the BR signaling—from the ligand perception, through cytoplasmic signal transduction, up to the BR-dependent gene expression, which is regulated by transcription factors and chromatin modifying enzymes. The identification of new components of the BR signaling is an ongoing process, however an emerging view of the BR signalosome indicates that this process is interconnected at various stages with other metabolic pathways. The signaling crosstalk is mediated by the BR signaling proteins, which function as components of the transmembrane BR receptor, by a cytoplasmic kinase playing a role of the major negative regulator of the BR signaling, and by the transcription factors, which regulate the BR-dependent gene expression and form a complicated regulatory system. This molecular network of interdependencies allows a balance in homeostasis of various phytohormones to be maintained. Moreover, the components of the BR signalosome interact with factors regulating plant reactions to environmental cues and stress conditions. This intricate network of interactions enables a rapid adaptation of plant metabolism to constantly changing environmental conditions.

Exploring the Brassinosteroid Signaling in Monocots Reveals Novel Components of the Pathway and Implications for Plant Breeding

“…These results are particularly important given the fact that drought belongs to the most limiting abiotic conditions for crop yield [15,21,22]. Therefore, currently the BR signaling is considered as an ideal target pathway for biotechnological modification to improve crop yield and stress tolerance, especially in the face of global climate change [23][24][25].…”

“…As a result of intensive research conducted for the last three decades in the model, dicot species Arabidopsis thaliana the BR signaling is one of the best described molecular processes in plants [25][26][27][28][29][30]. The intensive studies conducted with various approaches in Arabidopsis led to identification of numerous components of the BR signaling [26,31,32].…”

“…The intensive studies conducted with various approaches in Arabidopsis led to identification of numerous components of the BR signaling [26,31,32]. Moreover, recent reports indicated that various components of the BR signaling function as nodes of interactions with diverse signal transduction pathways of other phytohormones or environmental cues [25,33,34]. These integration hubs allow for a coordinated regulation of diverse physiological processes in reaction to environmental and stress conditions, as well as a rapid and efficient plant adaptation [25,29].…”

“…Moreover, recent reports indicated that various components of the BR signaling function as nodes of interactions with diverse signal transduction pathways of other phytohormones or environmental cues [25,33,34]. These integration hubs allow for a coordinated regulation of diverse physiological processes in reaction to environmental and stress conditions, as well as a rapid and efficient plant adaptation [25,29]. However, the network of the signaling interactions (crosstalk) appears to be very complicated, and therefore remains not fully understood.…”

“…When compared with the BR signaling model described in Arabidopsis, our current knowledge about mechanism of the BR signaling in monocots (including cereal crops) is still rather limited [24,35,36]. Among the monocots, the BR signaling process has been described to the greatest degree in rice [25] and will be presented as a model and reference for other monocots in this review (an updated model of the BR signaling and the BR-dependent regulation of gene expression in rice will be presented in the consecutive figures). However, even in rice a detailed mechanism of the BR signaling, especially the BR-induced protein phosphorylation/dephosphorylation-mediated relay which occurs in the cytoplasm, remains not fully understood [37,38].…”