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Brassinosteroids (BRs) are steroidal phytohormones that are essential for plant growth, development and adaptation to environmental stresses. BRs act in a dose-dependent manner and do not travel over long distances; hence, BR homeostasis maintenance is critical for their function. Biosynthesis of bioactive BRs relies on the cell-to-cell movement of hormone precursors. However, the mechanism of the short-distance BR transport is unknown, and its contribution to the control of endogenous BR levels remains unexplored. Here we demonstrate that plasmodesmata (PD) mediate the passage of BRs between neighboring cells. Intracellular BR content, in turn, is capable of modulating PD permeability to optimize its own mobility, thereby manipulating BR biosynthesis and signaling. Our work uncovers a thus far unknown mode of steroid transport in eukaryotes and exposes an additional layer of BR homeostasis regulation in plants.
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Updates on BES1/BZR1 Regulatory Networks Coordinating Plant Growth and Stress Responses
Brassinosteroids (BRs) play pivotal roles in the regulation of many dimensions of a plant’s life. Hence, through extensive efforts from many research groups, BR signaling has emerged as one of the best-characterized plant signaling pathways. The key molecular players of BR signaling from the cell surface to the nucleus important for the regulation of plant growth and development are well-established. Recent data show that BRs also modulate plant responses to environmental stresses such as drought and pathogen infection. In this mini review, we present the recent progress in BR signaling specifically in the post-translational SUMO modification of BR’s master regulators, BES1/BZR1. We also discuss recent findings on the crosstalk between BR, UV light, and jasmonic acid signaling pathways to balance growth during light stress and pathogen infections. Finally, we describe the current update on the molecular link between BR signaling and intracellular auxin transport that essential for plant development.
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- Award ID(s):
- 1818160
- PAR ID:
- 10290363
- Date Published:
- Journal Name:
- Frontiers in Plant Science
- Volume:
- 11
- ISSN:
- 1664-462X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The plant-specific TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) transcription factor family is most closely associated with regulating plant developmental programs. Recently, TCPs were also shown to mediate host immune signaling, both as targets of pathogen virulence factors and as regulators of plant defense genes. However, comprehensive characterization of TCP gene targets is still lacking. Loss of function of the class I TCP gene AtTCP8 attenuates early immune signaling and, when combined with mutations in AtTCP14 and AtTCP15, additional layers of defense signaling in Arabidopsis (Arabidopsis thaliana). Here, we focus on TCP8, the most poorly characterized of the three to date. We used chromatin immunoprecipitation and RNA sequencing to identify TCP8-bound gene promoters and differentially regulated genes in the tcp8 mutant; these datasets were heavily enriched in signaling components for multiple phytohormone pathways, including brassinosteroids (BRs), auxin, and jasmonic acid. Using BR signaling as a representative example, we showed that TCP8 directly binds and activates the promoters of the key BR transcriptional regulatory genes BRASSINAZOLE-RESISTANT1 (BZR1) and BRASSINAZOLE-RESISTANT2 (BZR2/BES1). Furthermore, tcp8 mutant seedlings exhibited altered BR-responsive growth patterns and complementary reductions in BZR2 transcript levels, while TCP8 protein demonstrated BR-responsive changes in subnuclear localization and transcriptional activity. We conclude that one explanation for the substantial targeting of TCP8 alongside other TCP family members by pathogen effectors may lie in its role as a modulator of BR and other plant hormone signaling pathways.more » « less
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Brassinosteroids (BR) and Target of Rapamycin Complex (TORC) are two major actors coordinating plant growth and stress responses. BRs function through a signaling pathway to extensively regulate gene expression and TORC is known to regulate translation and autophagy. Recent studies have revealed connections between these two pathways, but a system-wide view of their interplay is still missing. • We quantified the level of 23,975 transcripts, 11,183 proteins, and 27,887phosphorylation sites in wild-type Arabidopsis thalianaand inmutants with altered levels of either BRASSINOSTEROID INSENSITIVE 2 (B IN2) or REGULATORY ASSOCIATED PROTEIN OF TOR 1B (RAPTOR1B), two key players in BR and TORC signaling, respectively.• We found that perturbation of BIN2 or RAPTOR1B levels affects a common set of gene-products involved in growth and stress responses. Furthermore, we used the multi-omic data to reconstruct an integrated signaling network. We screened 41candidate genes identified from the reconstructed network and found that loss of function mutants of many of these proteins led to an altered BR response and/or modulated autophagy activity.• Altogether, these results establish a predictive network that defines different layers of molecular interactions between BR- or TORC-regulated growth and autophagy.more » « less
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Weijers, D.; Ljung, K.; Estelle, M.; Leyser, O. (Ed.)The plant hormone auxin governs many aspects of normal plant growth and development. Auxin also plays an important role in plant–microbe interactions, including interactions between plant hosts and pathogenic microorganisms that cause disease. It is now well established that indole-3-acetic acid (IAA), the most well-studied form of auxin, promotes disease in many plant–pathogen interactions. Recent studies have shown that IAA can act both as a plant hormone that modulates host signaling and physiology to increase host susceptibility and as a microbial signal that directly impacts the pathogen to promote virulence, but large gaps in our understanding remain. In this article, we review recent studies on the roles that auxin plays during plant–pathogen interactions and discuss the virulence mechanisms that many plant pathogens have evolved to manipulate host auxin signaling and promote pathogenesis.more » « less
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Abstract Brassinosteroids (BRs) are plant steroid hormones that regulate cell division and stress response. Here we use a systems biology approach to integrate multi-omic datasets and unravel the molecular signaling events of BR response inArabidopsis. We profile the levels of 26,669 transcripts, 9,533 protein groups, and 26,617 phosphorylation sites fromArabidopsisseedlings treated with brassinolide (BL) for six different lengths of time. We then construct a network inference pipeline called Spatiotemporal Clustering and Inference of Omics Networks (SC-ION) to integrate these data. We use our network predictions to identify putative phosphorylation sites on BES1 and experimentally validate their importance. Additionally, we identify BRONTOSAURUS (BRON) as a transcription factor that regulates cell division, and we show thatBRONexpression is modulated by BR-responsive kinases and transcription factors. This work demonstrates the power of integrative network analysis applied to multi-omic data and provides fundamental insights into the molecular signaling events occurring during BR response.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fpls.2020.617162
