The B-box bridge between light and hormones in plants

Vaishak, K.P.; Yadukrishnan, Premachandran; Bakshi, S. K.; Kushwaha, A. K. S.; Ramachandran, Harshil; Job, Nikhil; Babu, Dion; Datta, Sourav

doi:10.1016/j.jphotobiol.2018.12.021

Cited by 78 publications

(44 citation statements)

References 124 publications

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“…Light‐directed seedling growth (photomorphogenesis) is one of the best‐characterized examples of a highly dense regulatory network. Small molecule hormones are critical for relaying information about the light environment, as well as a diverse set of additional metabolic, environmental, and developmental cues (Vaishak et al, ; de Wit, Galvão, & Fankhauser, ). Hormones like auxin and brassinosteroids (BRs) play a central role in coordinating growth during photomorphogenesis.…”

Section: Introductionmentioning

confidence: 99%

Auxin promotion of seedling growth via ARF5 is dependent on the brassinosteroid‐regulated transcription factors BES1 and BEH4

Galstyan

Nemhauser

2019

Plant Direct

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Seedlings must continually calibrate their growth in response to the environment. Auxin and brassinosteroids (BRs) are plant hormones that work together to control growth responses during photomorphogenesis. We used our previous analysis of promoter architecture in an auxin and BR target gene to guide our investigation into the broader molecular bases and biological relevance of transcriptional co‐regulation by these hormones. We found that the auxin‐regulated transcription factor Auxin Responsive Factor 5 (ARF5) and the brassinosteroid‐regulated transcription factor BRI1‐EMS‐Suppressor 1/Brassinazole Resistant 2 (BES1) co‐regulated a subset of growth‐promoting genes via conserved bipartite cis ‐regulatory elements. Moreover, ARF5 binding to DNA could be enriched by increasing BES1 levels. The evolutionary loss of bipartite elements in promoters results in loss of hormone responsiveness. We also identified another member of the BES1/BZR1 family called BEH4 that acts partially redundantly with BES1 to regulate seedling growth. Double mutant analysis showed that BEH4 and not BZR1 were required alongside BES1 for normal auxin response during early seedling development. We propose that an ARF5‐BES1/BEH4 transcriptional module acts to promote growth via modulation of a diverse set of growth‐associated genes.

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Section: Introductionmentioning

confidence: 99%

Auxin promotion of seedling growth via ARF5 is dependent on the brassinosteroid‐regulated transcription factors BES1 and BEH4

Galstyan

Nemhauser

2019

Plant Direct

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“…COP1 and SPA proteins differ in their N-termini; while COP1 has a RING-finger domain, SPA proteins contain kinase-like domains (4,5). The COP1/SPA complex targets numerous transcription factors that regulate gene expression in response to light signals, including ELONGATED HYPOCOTYL5 (HY5) (6), its homolog HYH (7), LONG HYPOCOTYL IN FAR-RED1 (HFR1) (8,9), SALT TOLERANCE (STO), its homolog STH (10), SHI-RELATED SEQUENCE5 (11), CONSTANS (CO) and other BBX family proteins (12)(13)(14)(15)(16)(17)(18) and PRODUCTION OF ANTHOCYANIN PIGMENT (PAP) proteins (19). On light exposure, the photoreceptors cryptochromes and phytochromes directly interact with the COP1/SPA complex to suppress the E3 ubiquitin ligase activity of COP1/SPA, thereby stabilizing the downstream transcription factors (2).…”

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confidence: 99%

Cryptochrome 2 competes with COP1 substrates to repress COP1 ubiquitin ligase activity during Arabidopsis photomorphogenesis

Ponnu

Riedel

Penner

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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In plants, the cryptochrome photoreceptors suppress the activity of the COP1/SPA ubiquitin ligase to initiate photomorphogenesis in blue light. Both CRY1 and CRY2 interact with the COP1/SPA complex in a blue light-dependent manner. The mechanisms underlying the inhibition of COP1 activity through direct interactions with photoactivated CRYs are not fully understood. Here we tested the hypothesis that CRY2 inhibits COP1 by displacing the degradation substrates from COP1. To this end, we analyzed the role of a conserved valine-proline (VP) motif in the C-terminal domain of CRY2 (CCT2), which resembles the core COP1-WD40–binding sequences present in the substrates of COP1. We show that the VP motif in CRY2 is essential for the interaction of CRY2 with COP1 in yeast two-hybrid assays andin planta. Mutations in the VP motif of CRY2 abolished the CRY2 activity in photomorphogenesis, indicating the importance of VP. The interaction between COP1 and its VP-containing substrate PAP2 was prevented in the presence of coexpressed CRY2, but not in the presence of CRY2 carrying a VP mutation. Thus, since both PAP2 and CRY2 engage VP motifs to bind to COP1, these results demonstrate that CRY2 outcompetes PAP2 for binding to COP1. We further found that the previously unknown interaction between SPA1-WD and CCT2 occurs via the VP motif in CRY2, suggesting structural similarities in the VP-binding pockets of COP1-WD40 and SPA1-WD40 domains. A VP motif present in CRY1 is also essential for binding to COP1. Thus, CRY1 and CRY2 might share this mechanism of COP1 inactivation.

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“…This indicates that COL4 has important functions in plants besides flowering control, similar to other COLs and BBX family members. Recent publications discuss a linkage between COLs and BBX proteins being involved in plant developmental processes spanning over transition to flowering, seedling de-etiolation, photomorphogenesis, responses to antibiotic stress and shade avoidance, plant architecture, e.g., branching, circadian clock regulations and hormone signaling (Ledger et al, 2001; Cheng and Wang, 2005; Datta et al, 2006; Hassidim et al, 2009; Wang et al, 2013; Wang and Dehesh, 2015; Graeff et al, 2016; Tripathi et al, 2016, for review see: Vaishak et al, 2019). The COLs, especially CO, form heterodimers with other BBX proteins while being mediated into larger protein complexes and inactivated that subsequently alters the flowering habit.…”

Section: Discussionmentioning

confidence: 99%

The Arabidopsis thalianaCONSTANS-LIKE 4 (COL4) – A Modulator of Flowering Time

Steinbach

2019

Front. Plant Sci.

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Appropriate control of flowering time is crucial for crop yield and the reproductive success of plants. Flowering can be induced by a number of molecular pathways that respond to internal and external signals. In Arabidopsis, expression of the key florigenic signal FLOWERING LOCUS T ( FT ) is positively regulated by CONSTANS (CO) a BBX protein sharing high sequence similarity with 16 CO-like proteins. Within this study, we investigated the role of the Arabidopsis CONSTANS - LIKE 4 ( COL4) , whose role in flowering control was unknown. We demonstrate that, unlike CO, COL4 is a flowering repressor in long days (LD) and short days (SD) and acts on the expression of FT and FT -like genes as well as on SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 ( SOC1 ). Reduction of COL4 expression level leads to an increase of FT and APETALA 1 ( AP1 ) expression and to accelerated flowering, while the increase of COL4 expression causes a flowering delay. Further, the observed co-localization of COL4 protein and CO in nuclear speckles supports the idea that the two act as an antagonistic pair of transcription factors. This interaction may serve the fine-tuning of flowering time control and other light dependent plant developmental processes.

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The B-box bridge between light and hormones in plants

Cited by 78 publications

References 124 publications

Auxin promotion of seedling growth via ARF5 is dependent on the brassinosteroid‐regulated transcription factors BES1 and BEH4

Auxin promotion of seedling growth via ARF5 is dependent on the brassinosteroid‐regulated transcription factors BES1 and BEH4

Cryptochrome 2 competes with COP1 substrates to repress COP1 ubiquitin ligase activity during Arabidopsis photomorphogenesis

The Arabidopsis thalianaCONSTANS-LIKE 4 (COL4) – A Modulator of Flowering Time

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