Class I TCP transcription factor AtTCP8 modulates key brassinosteroid-responsive genes

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 data sets 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.

Physiological Roles and Mechanisms of Action of Class I TCP Transcription Factors

“…For example, TCP8 interacts with SRFR1 in nuclear foci, but TCP8-PNM1 complexes were detected in the nucleoplasm in BiFC assays [ 91 , 140 ]. Furthermore, TCP8 nuclear localization seems to be affected by interaction with BZR1 [ 141 ]. As observed with homodimers, TCP15 was detected in the nucleoplasm when interacting with SRFR1, MYB106 and GLK1 [ 66 , 79 , 91 ].…”

Systematic Investigation of TCP Gene Family: Genome-Wide Identification and Light-Regulated Gene Expression Analysis in Pepino (Solanum Muricatum)

“…AtTCP1 , AtTCP12 , and AtTCP18 in the CYC/TB1 class regulate lateral branch formation and flower development [ 41 ]. AtTCP8 , AtTCP14 , AtTCP15 , AtTCP22 , and AtTCP23 , belonging to the Class I subfamily, play a crucial role in regulating leaf development through the cell cycle and the gene network maintained by stem apical meristem [ 42 , 43 ]. Genes in the CIN subcluster, such as AtTCP2 , are regulated by miRNA319 [ 44 , 45 ], which acts as a negative regulator of cell proliferation and controls leaf margin growth.…”

Gene expression and expression quantitative trait loci analyses uncover natural variations underlying the improvement of important agronomic traits during modern maize breeding

“…In Arabidopsis, AtARF6 , the ortholog of the ZmARF34 gene, acts through activating the transcription of a key brassinosteroid (BR) biosynthetic enzyme DWARF4 to regulate leaf and sepal proximodistal growth (Xiong et al., 2021). AtTCP8 , the ortholog of the ZmTCP40 gene in Arabidopsis, could directly activate the expression of the key BR transcriptional regulatory genes BRASSINAZOLE‐RESISTANT 1 ( BZR1 ) and BRASSINAZOLE‐RESISTANT 2 ( BZR2/BES1 ) (Spears et al., 2022). BR signaling plays an important role in influencing leaf angle development (Fang et al., 2020; Min et al., 2019).…”