The Trithorax Group Factor ULTRAPETALA1 Regulates Developmental as Well as Biotic and Abiotic Stress Response Genes in Arabidopsis

Abstract

In eukaryotes, Polycomb group (PcG) and trithorax group (trxG) factors oppositely regulate gene transcription during development through histone modifications, with PcG factors repressing and trxG factors activating the expression of their target genes. Although plant trxG factors regulate many developmental and physiological processes, their downstream targets are poorly characterized. Here we use transcriptomics to identify genome-wide targets of the Arabidopsis thaliana trxG factor ULTRAPETALA1 (ULT1) during vegetative and reproductive development and compare them with those of the PcG factor CURLY LEAF (CLF). We find that genes involved in development and transcription regulation are over-represented among ULT1 target genes. In addition, stress response genes and defense response genes such as those in glucosinolate metabolic pathways are enriched, revealing a previously unknown role for ULT1 in controlling biotic and abiotic response pathways. Finally, we show that many ULT1 target genes can be oppositely regulated by CLF, suggesting that ULT1 and CLF may have antagonistic effects on plant growth and development in response to various endogenous and environmental cues.

Whether Gametophytes Are Reduced or Unreduced in Angiosperms Might Be Determined Metabolically

“…These are then stabilized by PCR2 H3K27me3 silencing marks [50]. ULTRAPETALA1 (ULT1) is a trithorax factor that functions as an anti-repressor to counteract PcG silencing at 1000s of loci, including many genes where specific up or downregulation is required for normal reproductive development [51,52]. The upregulation in B. stricta of AL7 and ULT1 genes (Figure 5a-c) is further evidence that floral development at the molecular level was strongly supported in sexual B. stricta but weakly supported in apomictic B.…”

The Epigenetic Faces of ULTRAPETALA1

“…This model suggests that ULT1 not only acts to antagonize the PcG activity; instead, it could act together with PRC2, maintaining the repression states of some targets, through the maintenance of the H3K27me3 mark ( Figure 3D). For instance, it has been seen that the ult1 mutants have more upregulated genes than down-regulated genes (Xu et al, 2018;Tyler et al, 2019). Interestingly, the MADSbox FLOWERING LOCUS C (FLC) gene, which is activated by TrxG and repressed by PcG (Whittaker and Dean, 2017), is upregulated (∼4.35 fold) in ult1 mutant plants (Pu et al, 2013;Xu et al, 2018;Tyler et al, 2019), contrary to what is expected for TrxG mutants.…”

“…For instance, it has been seen that the ult1 mutants have more upregulated genes than down-regulated genes (Xu et al, 2018;Tyler et al, 2019). Interestingly, the MADSbox FLOWERING LOCUS C (FLC) gene, which is activated by TrxG and repressed by PcG (Whittaker and Dean, 2017), is upregulated (∼4.35 fold) in ult1 mutant plants (Pu et al, 2013;Xu et al, 2018;Tyler et al, 2019), contrary to what is expected for TrxG mutants. Besides, ULT1 binding to the FLC locus supports a direct regulation (Xu et al, 2018).…”

“…Genome-wide analyses have revealed that ULT1-regulated genes are involved in different developmental processes (Tyler et al, 2019). Besides its function in SAM development (Fletcher, 2001), ULT1 participates in different stress processes (Pu et al, 2013;Tyler et al, 2019).…”

“…Genome-wide analyses have revealed that ULT1-regulated genes are involved in different developmental processes (Tyler et al, 2019). Besides its function in SAM development (Fletcher, 2001), ULT1 participates in different stress processes (Pu et al, 2013;Tyler et al, 2019). In addition, we recently found that ULT1 is necessary for root stem cell niche (SCN) maintenance ( Figure 3C), including the cell division rate of the Quiescent Center (QC) and the undifferentiated state of the columella stem cells (Ornelas-Ayala et al, 2020).…”