AUTHOR=Wang Chenggang , Du Xuezhu , Mou Zhonglin 

TITLE=The Mediator Complex Subunits MED14, MED15, and MED16 Are Involved in Defense Signaling Crosstalk in Arabidopsis

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.01947

DOI=10.3389/fpls.2016.01947

ISSN=1664-462X

ABSTRACT=<p>Mediator is a highly conserved protein complex that functions as a transcriptional coactivator in RNA polymerase II (RNAPII)-mediated transcription. The <italic>Arabidopsis</italic> Mediator complex has recently been implicated in plant immune responses. Here, we compared salicylic acid (SA)-, methyl jasmonate (MeJA)-, and the ethylene (ET) precursor 1-aminocyclopropane-1-carboxylic acid (ACC)-induced defense and/or wound-responsive gene expression in 14 <italic>Arabidopsis</italic> Mediator subunit mutants. Our results show that MED14, MED15, and MED16 are required for SA-activated expression of the defense marker gene <italic>PATHOEGNESIS-RELATED GENE1</italic>, MED25 is required for MeJA-induced expression of the wound-responsive marker gene <italic>VEGATATIVE STORAGE PROTEIN1</italic> (<italic>VSP1</italic>), MED8, MED14, MED15, MED16, MED18, MED20a, MED25, MED31, and MED33A/B (MED33a and MED33B) are required for MeJA-induced expression of the defense maker gene <italic>PLANT DEFENSIN1.2</italic> (<italic>PDF1.2</italic>), and MED8, MED14, MED15, MED16, MED25, and MED33A/B are also required for ACC-triggered expression of <italic>PDF1.2</italic>. Furthermore, we investigated the involvement of MED14, MED15, and MED16 in plant defense signaling crosstalk and found that MED14, MED15, and MED16 are required for SA- and ET-mediated suppression of MeJA-induced <italic>VSP1</italic> expression. This result suggests that MED14, MED15, and MED16 not only relay defense signaling from the SA and JA/ET defense pathways to the RNAPII transcription machinery, but also fine-tune defense signaling crosstalk. Finally, we show that MED33A/B contributes to the necrotrophic fungal pathogen <italic>Botrytis cinerea-</italic>induced expression of the defense genes <italic>PDF1.2, HEVEIN-LIKE</italic>, and <italic>BASIC CHITINASE</italic> and is required for full-scale basal resistance to <italic>B. cinerea</italic>, demonstrating a positive role for MED33 in plant immunity against necrotrophic fungal pathogens.</p>