The Mediator subunit SFR6/MED16 controls defence gene expression mediated by salicylic acid and jasmonate responsive pathways

Abstract

Summary Arabidopsis SENSITIVE TO FREEZING6 (SFR6) controls cold‐ and drought‐inducible gene expression and freezing‐ and osmotic‐stress tolerance. Its identification as a component of the MEDIATOR transcriptional co‐activator complex led us to address its involvement in other transcriptional responses. Gene expression responses to Pseudomonas syringae, ultraviolet‐C (UV‐C) irradiation, salicylic acid (SA) and jasmonic acid (JA) were investigated in three sfr6 mutant alleles by quantitative real‐time PCR and susceptibility to UV‐C irradiation and Pseudomonas infection were assessed. sfr6 mutants were more susceptible to both Pseudomonas syringae infection and UV‐C irradiation. They exhibited correspondingly weaker PR (pathogenesis‐related) gene expression than wild‐type Arabidopsis following these treatments or after direct application of SA, involved in response to both UV‐C and Pseudomonas infection. Other genes, however, were induced normally in the mutants by these treatments. sfr6 mutants were severely defective in expression of plant defensin genes in response to JA; ectopic expression of defensin genes was provoked in wild‐type but not sfr6 by overexpression of ERF5. SFR6/MED16 controls both SA‐ and JA‐mediated defence gene expression and is necessary for tolerance of Pseudomonas syringae infection and UV‐C irradiation. It is not, however, a universal regulator of stress gene transcription and is likely to mediate transcriptional activation of specific regulons only.

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

“…5), suggesting that MED16 may directly participate in both EIN3/EIL1-and AP2/ERF-mediated transcription. Consistent with this hypothesis, elevated expression of PDF1.2 activated by the overexpression of ERF5 depends on MED16 (Wathugala et al, 2012). Furthermore, EIN3, EIL1, ORA59, and ERF1 have all been shown to interact with MED25, a Mediator subunit physically associating with MED16 (Çevik et al, 2012;Yang et al, 2014).…”

“…and Wathugala et al (2012) have shown that mutations in MED16 block JA/ET-and B. cinerea-induced defense gene expression and compromise resistance to B. cinerea and A. brassicicola. It has been well documented that expression of the defense gene PDF1.2 is regulated by a group of AP2/ERF domain transcription factors including ORA59 and ERF1 (Lorenzo et al, 2003;Pré et al, 2008) and that genes encoding the AP2/ERF factors are, in turn, controlled by the transcription factors EIN3 and EIL1 (Solano et al, 1998;Zhu et al, 2011).…”

“…Since MED16 positively regulates both SA and JA/ET signaling (Wathugala et al, 2012;Zhang et al, 2012), we wondered how SA and JA/ET pathway genes were influenced by the med16-1 mutation during S. sclerotiorum infection. To this end, we further explored the microarray data and identified SA and JA/ET pathway genes that showed a 2-fold or larger difference in their expression levels with a low q value (q # 0.05) between med16-1 and the wild type (Table I).…”

Identification of MEDIATOR16 as the Arabidopsis COBRA suppressor MONGOOSE1

“…SFR6 was identified as MED16, a component of the MEDIATOR transcriptional coactivator complex (31), and is required for RNA polymerase II recruitment of genes regulated by the CBF transcription factor (34). More generally, MED16 has been shown to regulate expression of multiple genes associated with a variety of biological functions (31,34). To identify potential targets of MED16 that are involved in cobra suppression, we performed RNA-sequencing (seq) analysis on 7-d-old seedlings of wild type, cob-6, sfr6-3, and sfr6-3 cob-6 (Fig.…”

“…The Arabidopsis mediator complex was purified (28) and, in combination with subsequent bioinformatic analysis (25), 34 subunits were identified, a number of these specific to plants (29). In Arabidopsis, roles for Mediator subunits have been demonstrated in the transcriptional response to a number of biotic (30)(31)(32) and abiotic stress conditions (33,34) as well as in plant development (35,36).…”