MEDIATOR18 influences Arabidopsis root architecture, represses auxin signaling and is a critical factor for cell viability in root meristems

Abstract

Summary The Mediator (MED) complex plays a key role in the recruitment and assembly of the transcription machinery for the control of gene expression. Here, we report on the role of MEDIATOR18 (MED18) subunit in root development, auxin signaling and meristem cell viability in Arabidopsis thaliana seedlings. Loss‐of‐function mutations in MED18 reduce primary root growth, but increase lateral root formation and root hair development. This phenotype correlates with alterations in cell division and elongation likely caused by an increased auxin response and transport at the root tip, as evidenced by DR5:GFP, pPIN1::PIN1‐GFP, pPIN2::PIN2‐GFP and pPIN3::PIN3‐GFP auxin‐related gene expression. Noteworthy, med18 seedlings manifest cell death in the root meristem, which exacerbates with age and/or exposition to DNA‐damaging agents, and display high expression of the cell regeneration factor ERF115. Cell death in the root tip was reduced in med18 seedlings grown in darkness, but remained when only the shoot was exposed to light, suggesting that MED18 acts to protect root meristem cells from local cell death, and/or in response to root‐acting signal(s) emitted by the shoot in response to light stimuli. These data point to MED18 as an important component for auxin‐regulated root development, cell death and cell regeneration in root meristems.

Specific functions for Mediator complex subunits from different modules in the transcriptional response of Arabidopsis thaliana to abiotic stress

“…These TFs have been implicated as central regulators of the low-energy transcriptional response which may overlap with the abiotic stress response 92 , and the data presented here implicate MED18 as a co-regulator during salt stress. bZIP11 and MED18 have both been implicated in auxin-mediated transcription, suggesting a possible integration point for these signaling pathways 93,94 . Our results also identify a putative interaction between MED18 and light signaling pathways via the PIF1/PIF3 TFs.…”

Physiological and Transcriptomic Changes during the Early Phases of Adventitious Root Formation in Mulberry Stem Hardwood Cuttings

“…In the current study, the AP2/EREBP family presented the most responsive common DEGs compared to the other families. Genes of this family showed a global up-regulation, which was closely associated with auxin and cytokinin signaling in root regeneration [68,69,70]. A good example is RAP2.6L , which was involved in pith cell division and displayed a great induction in response to the reduced auxin level at the lower side of incision in Arabidopsis stems [71].…”

PP7L is essential for MAIL1‐mediated transposable element silencing and primary root growth

“…In agreement, impaired root growth and spontaneous cell death in the RAM was also described for mutants with defects in DNA replication, DNA repair, or chromatin assembly. Examples are mutants lacking components of the mediator complex (Raya‐Gonzalez et al , ) or with disrupted function of the homologue of yeast DNA Replication Helicase/Nuclease 2 (Jia et al , ), as well as mutants with impaired function of histone chaperone complexes (Ma et al , ) or with defects in structural components of the chromatin (Diaz et al , ).…”