Biology subjects

Spears, B. J.

Publications and source records attributed to Spears, B. J..

3 recordsLinked to original sources

bioRxiv2025

Regulation of brassinosteroid signaling through Arabidopsis transcription factor TCP8 by a conserved post-translational mechanism

The ability of plants to respond to changing environmental conditions is dependent on their capacities to produce fast, transient, and reversible changes to stress-responsive gene expression profiles. Post-translation modification of transcription factors has been identified as a contributing mechanism to these responses but has yet to be explored mechanistically in the TCPs, a plant-specific TF family known to be broadly involved in phytohormone signaling governing biotic and abiotic stress responses. Here, we use a recombinant expression system and proteomic approach to identify the specific residues at which AtTCP8 is covalently modified by the small peptide SUMO and demonstrate that loss of key lysine residues abolishes modification of the TF. We validate these observations by demonstrating the failure of a sumoylation-site-deficient AtTCP8 mutant to complement a known tcp8 BR signaling deficiency phenotype natively in Arabidopsis and reduced transcriptional activity of the protein at a known regulatory target promoter. Further, we show that class I TCP orthologs in the model non-vascular plant Physcomitrium patens are sumoylated as well in our system, a novel finding for TFs in this organism. These data support a conserved model for post-translational regulation by SUMO of phytohormone-responsive gene expression between vascular and non-vascular plants.

plant biology↗

bioRxiv2021

The class I TCP transcription factor AtTCP8 is a modulator of phytohormone-responsive signaling networks

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 regulators of plant defense genes. However, any comprehensive characterization of TCP gene targets is still lacking. Loss of the class I TCP AtTCP8 attenuates early immune signaling, and when combined with mutations in AtTCP14 and AtTCP15, additional layers of defense signaling in Arabidopsis thaliana. Here we focus on TCP8, the most poorly characterized of the three to date. We use chIP and RNA-sequencing to identify TCP8-bound gene promoters and differentially regulated genes in the tcp8 mutant, data sets that are heavily enriched in signaling components for multiple phytohormone pathways, including brassinosteroids (BRs), auxin, and jasmonic acid (JA). Using BR signaling as a representative example, we show that TCP8 directly binds and activates the promoters of the key BR transcriptional regulators BZR1 and BZR2/BES1. Furthermore, tcp8 mutant seedlings exhibit altered BR-responsive growth patterns and complementary reductions in BZR2 transcript levels, while the expressed protein demonstrates BR-responsive changes in subnuclear localization and transcriptional activity. We conclude that one explanation for the significant targeting of TCP8 alongside other TCP family members by pathogen effectors may lie in its role as a modulator of brassinosteroid and other plant hormone signaling pathways. One Sentence SummaryOne member of a pathogen-targeted transcription factor family modulates phytohormone response networks and displays brassinosteroid-dependent cellular location and activity.

plant biology↗

bioRxiv2020

Opposing functions of the plant TOPLESS gene family during SNC1-mediated autoimmunity

Regulation of the plant immune system is important for controlling the specificity and amplitude of responses to pathogens and in preventing growth-inhibiting autoimmunity that leads to reductions in plant fitness. In previous work, we reported that SRFR1, a negative regulator of effector-triggered immunity, interacts with SNC1 and EDS1. When SRFR1 is non-functional in the Arabidopsis accession Col-0, SNC1 levels increase, causing a cascade of events that lead to autoimmunity phenotypes. Previous work showed that some members of the transcriptional co-repressor family TOPLESS interact with SNC1 to repress negative regulators of immunity. Therefore, to explore potential connections between SRFR1 and TOPLESS family members, we took a genetic approach that examined the effect of each TOPLESS member in the srfr1 mutant background. The data indicated that an additive genetic interaction exists between SRFR1 and two members of the TOPLESS family, TPR2 and TPR3, as demonstrated by increased stunting and elevated PR2 expression in srfr1 tpr2 and srfr1 tpr2 tpr3 mutants. Furthermore, the tpr2 mutation intensifies autoimmunity in the auto-active snc1-1 mutant, indicating a novel role of these TOPLESS family members in negatively regulating SNC1-dependent phenotypes. This negative regulation can also be reversed by overexpressing TPR2 in the srfr1 tpr2 background. Thus, this work uncovers diverse functions of individual members of the TOPLESS family in Arabidopsis and provides evidence for the additive effect of transcriptional and post-transcriptional regulation of SNC1. Author SummaryThe immune system is a double-edged sword that affords organisms with protection against infectious diseases but can also lead to negative effects if not properly controlled. Plants only possess an innate antimicrobial immune system that relies on rapid upregulation of defenses once immune receptors detect the presence of microbes. Plant immune receptors known as resistance proteins play a key role in rapidly triggering defenses if pathogens breach other defenses. A common model of unregulated immunity in the reference Arabidopsis variety Columbia-0 involves a resistance gene called SNC1. When the SNC1 protein accumulates to unnaturally high levels or possesses auto-activating mutations, the visible manifestations of immune overactivity include stunted growth and low biomass and seedset. Consequently, expression of this gene and accumulation of the encoded protein are tightly regulated on multiple levels. Despite careful study the mechanisms of SNC1 gene regulation are not fully understood. Here we present data on members of the well-known TOPLESS family of transcriptional repressors. While previously characterized members were shown to function in indirect activation of defenses, TPR2 and TPR3 are shown here to function in preventing high defense activity. This study therefore contributes to the understanding of complex regulatory processes in plant immunity.

plant biology↗