CDK8 is associated with RAP2.6 and SnRK2.6 and positively modulates abscisic acid signaling and drought response in Arabidopsis

Abstract

Summary CDK8 is a key subunit of Mediator complex, a large multiprotein complex that is a fundamental part of the conserved eukaryotic transcriptional machinery. However, the biological functions of CDK8 in plant abiotic stress responses remain largely unexplored. Here, we demonstrated CDK8 as a critical regulator in the abscisic acid (ABA) signaling and drought response pathways in Arabidopsis. Compared to wild‐type, cdk8 mutants showed reduced sensitivity to ABA, impaired stomatal apertures and hypersensitivity to drought stress. Transcriptomic and chromatin immunoprecipitation analysis revealed that CDK8 positively regulates the transcription of several ABA‐responsive genes, probably through promoting the recruitment of RNA polymerase II to their promoters. We discovered that both CDK8 and SnRK2.6 interact physically with an ERF/AP2 transcription factor RAP2.6, which can directly bind to the promoters of RD29A and COLD‐REGULATED 15A (COR15A) with GCC or DRE elements, thereby promoting their expression. Importantly, we also showed that CDK8 is essential for the ABA‐induced expression of RAP2.6 and RAP2.6‐mediated upregulation of ABA‐responsive genes, indicating that CDK8 could link the SnRK2.6‐mediated ABA signaling to RNA polymerase II to promote immediate transcriptional response to ABA and drought signals. Overall, our data provide new insights into the roles of CDK8 in modulating ABA signaling and drought responses.

Mediator Complex: A Pivotal Regulator of ABA Signaling Pathway and Abiotic Stress Response in Plants

“…Recently, another subunit belonging to the Mediator kinase module termed as CDK8 , has been identified as a critical regulator in the ABA signaling pathway [ 48 ]. As described previously, SnRK2s need to be phosphorylated by certain protein kinases in order to further perform the ABA signaling process [ 36 ].…”

“…The CDK8 and its kinase module components are generally known as negative regulators of gene expression in yeast, metazoan cells, and plants [ 13 , 49 , 50 ]. However, increasing evidence is showing that CDK8 could also play a positive role in plant transcriptional regulation as expression of defense-responsive genes ( PDF1.2 , AACT1 and NPR1 ), salicylic acid (SA)-biosynthetic genes ( ICS1 and EDS5 ) and ABA-responsive genes such as RAP2.6 , RD29A , RD29B , and COR15A [ 44 , 48 , 51 , 52 ] are positively regulated by CDK8 in plants. Transcriptomic analysis has revealed that CDK8 affects approximately 30% of the ABA-responsive genes, most of these genes are downregulated in cdk8 mutants compared to WT.…”

“…In response to ABA, RAP2.6 could be enriched at the RD29A and COR15A promoters. These findings indicated the possibility that CDK8 may regulate the expression of ABA-responsive genes through RAP2.6 [ 48 ]. It may also be possible that other TFs interact with CDK8 to regulate the expression of ABA-responsive genes.…”

“…Abiotic stresses such as cold, high salinity, and drought are some of the environmental stimuli that plants get exposed to and they must be able to integrate these signals using different regulatory pathways if they are to survive [ 25 , 53 ]. Various subunits of the Mediator complex including CDK8, MED16, MED14, and MED25 have been identified to help plants to respond to these stresses [ 1 , 48 ]. We will summarize some of the findings that have been reported about the functions of these subunits in dealing with three abiotic stresses of cold, high salinity, and drought ( Figure 2 ).…”

“…In addition, CDK8 has also been indicated to participate in drought stress recently. CDK8 mutation results in higher stomatal density and impaired stomatal aperture, as well as reduced tolerance to drought [ 48 ]. Consistently, over-expression of CDK8 enhances the drought tolerance.…”