Mediator tail module subunits MED16 and MED25 differentially regulate abscisic acid signaling in Arabidopsis

Abstract

MED25 has been implicated as a negative regulator of the abscisic acid (ABA) signaling pathway. However, it is unclear whether other Mediator subunits could associate with MED25 to participate in the ABA response. Here, we used affinity purification followed by mass spectrometry to uncover Mediator subunits that associate with MED25 in transgenic plants. We found that at least 26 Mediator subunits, belonging to the head, middle, tail, and CDK8 kinase modules, were co‐purified with MED25 in vivo. Interestingly, the tail module subunit MED16 was identified to associate with MED25 under both mock and ABA treatments. We further showed that the disruption of MED16 led to reduced ABA sensitivity compared to the wild type. Transcriptomic analysis revealed that the expression of several ABA‐responsive genes was significantly lower in med16 than those in wild type. Furthermore, we discovered that MED16 may possibly compete with MED25 to interact with the key transcription factor ABA INSENSITIVE 5 (ABI5) to positively regulate ABA signaling. Consistently, med16 and med25 mutants displayed opposite phenotypes in ABA response, cuticle permeability, and differential ABI5‐mediated EM1 and EM6 expression. Together, our data indicate that MED16 and MED25 differentially regulate ABA signaling by antagonistically affecting ABI5‐mediated transcription in Arabidopsis.

The CBP/p300 histone acetyltransferases function as plant‐specific MEDIATOR subunits in Arabidopsis

“…Given that cell suspension cultures were used in the previous study (Backstrom et al, 2007) and seedlings were used in the current study, it is possible that the kinase module functions as a part of MEDIATOR in seedlings but not in cell suspension cultures. The inclusion of the kinase module in the Arabidopsis MEDIATOR complex was also supported by an independent study published in this issue (Guo et al, 2020), but the study did not identify CYCC1-1, CYCC1-2, MED30, MED31, HAC1, and HAC5 as subunits of the MEDIATOR complex in Arabidopsis.…”

SIZ1 negatively regulates aluminum resistance by mediating the STOP1–ALMT1 pathway in Arabidopsis

“…All Arabidopsis thaliana mutants and transgenic plants used were in the Columbia‐0 (Col‐0) ecotype background. siz1‐2 (SALK_065397), stop1 (SALK_114108), almt1 (SALK_ 009629), and med16‐2 (SALK_048091) are previously reported T‐DNA insertion mutants (Miura et al, 2005; Liu et al, 2009; Sawaki et al, 2009; Guo et al, 2020b) and sfr6‐1 carries a ethylmethane sulfonate (EMS)‐induced mutation of MED16 (Knight et al, 2009). The s iz1‐2/stop1 and siz1‐2/almt1 mutants were derived by crossing siz1‐2 with stop1 or almt1 .…”

Interconnection of iron and osmotic stress signalling in plants: is FIT a regulatory hub to cross‐connect abscisic acid responses?

“…Recently, it was found that MED16 interacts with ABI5 and positively affects ABA signalling (Guo et al . 2021). Gain‐ and loss‐of‐function studies demonstrated that EIN3/EIL1 is also necessary and sufficient for enhanced salt tolerance (Peng et al .…”