The Mediator Complex Subunit PFT1 Interferes with COP1 and HY5 in the Regulation of Arabidopsis Light Signaling      

Abstract

Arabidopsis (Arabidopsis thaliana) mutants hypersensitive to far-red light were isolated under a light program of alternating red and far-red light pulses and were named eid (for empfindlicher im dunkelroten Licht). The dominant eid3 mutant carries a missense mutation in a conserved domain of PHYTOCHROME AND FLOWERING TIME1 (PFT1), an important component of the plant mediator coactivator complex, which links promoter-bound transcriptional regulators to RNA polymerase II complexes. Epistatic analyses were performed to obtain information about the coaction between the mutated PFT1 eid3 and positively and negatively acting components of light signaling cascades. The data presented here provide clear evidence that the mutation mainly enhances light sensitivity downstream of phytochrome A (phyA) and modulates phyB function. Our results demonstrate that the Mediator component cooperates with CONSTITUTIVE PHOTORMORPHOGENIC1 in the regulation of light responses and that the hypersensitive phenotype strictly depends on the presence of the ELONGATED HYPOCOTYL5 transcription factor, an important positive regulator of light-dependent gene expression. Expression profile analyses revealed that PFT1 eid3 alters the transcript accumulation of light-regulated genes even in darkness. Our data further indicate that PFT1 regulates the floral transition downstream of phyA. The PFT1 missense mutation seems to create a constitutively active transcription factor by mimicking an early step in light signaling.

PHYTOCHROME AND FLOWERING TIME1/MEDIATOR25 Regulates Lateral Root Formation via Auxin Signaling in Arabidopsis

“…Emerging evidence indicates that PFT1/MED25 plays multiple roles in a number of essential plant processes, including light signaling and flowering time (Cerdán and Chory, 2003;Wollenberg et al, 2008;Iñigo et al, 2012;Klose et al, 2012), JA-mediated pathogen defense (Kidd et al, 2009), organ growth (Xu and Li, 2011), abiotic stress (Elfving et al, 2011), and JA and abscisic acid signaling (Çevik et al, 2012;Chen et al, 2012). This is consistent with the expectation that individual Mediator subunits recognize and respond to a subset of the approximately 1,500 transcription factors present in the Arabidopsis genome.…”

HEMERA Couples the Proteolysis and Transcriptional Activity of PHYTOCHROME INTERACTING FACTORs in Arabidopsis Photomorphogenesis

“…MED25 interacts directly with the transcriptional activation domain of VP16 (Vojnic et al, 2011). The ortholog of MED25 in Arabidopsis, known as PFT1 (Phytochrome and Flowering Time1) (Cerdán and Chory, 2003;Bäckström et al, 2007), was identified as a factor involved in phy signaling and flowering time (Cerdán and Chory, 2003;Iñigo et al, 2012aIñigo et al, , 2012bKlose et al, 2012). Our future investigation will test the hypothesis that HMR's 9aaTAD interacts directly with PFT1 to promote gene activation.…”

The Arabidopsis Mediator Complex Subunit16 Is a Key Component of Basal Resistance against the Necrotrophic Fungal Pathogen Sclerotinia sclerotiorum

“…For instance, the Arabidopsis MEDIATOR SUBUNIT14 (MED14)/STRUWWELPETER is a key regulator of cell proliferation (Autran et al, 2002). MED25/ PHYTOCHROME AND FLOWERING TIME1 was first identified as a key regulator of flowering (Cerdán and Chory, 2003) and later found to regulate final organ size and light signaling (Xu and Li, 2011;Klose et al, 2012). MED18 was found to control flowering time and floral organ identity (Zheng et al, 2013).…”