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

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 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.

Genome-Wide Identification of Binding Sites for SmTCP7a Transcription Factors of Eggplant during Bacterial Wilt Resistance by ChIP-Seq

“…Although both TCP classes can recognize some common cis-elements [ 32 ], the conserved DNA binding sites of class I and class II are quite distinct [ 1 ]. Several results have shown that class I TCPs, such as TCP8 [ 8 , 11 ], TC9 [ 10 ], TCP14 [ 20 ], TCP15 [ 26 ] and TCP23 [ 27 ], play a key role in plant disease resistance. Our polygenetic tree results showed that SmTCP7a is a class I TCP.…”

“…In Arabidopsis, AtTCP4, AtTCP9 and AtTCP20 can bind to the LOX2 promoter to regulate JA biosynthesis [ 9 ]. AtTCP8 can bind to the ICS1 promoter to regulate SA biosynthesis [ 9 , 10 ] as well as the key BR transcriptional regulators, BZR1 and BZR2/BES1 [ 11 ]. However, the molecular mechanism underlying their transcription control remains unclear.…”