The DORNRÖSCHEN/ENHANCER OF SHOOT REGENERATION1 Gene of Arabidopsis Acts in the Control of Meristem Cell Fate and Lateral Organ Development

Abstract

The two main tasks of a meristem, self-perpetuation and organ initiation, are separated spatially. Slowly dividing cells in the meristem center act as pluripotent stem cells, and only their derivatives in the meristem periphery specify new organs. Meristem integrity and cellular proliferation are controlled in part by regulatory interactions between genes that are expressed in specific subdomains of the meristem. Using transposon-mediated activation tagging, we have identified Dornröschen ( drn-D ) mutants of Arabidopsis that prematurely arrest shoot meristem activity with the formation of radialized lateral organs. The mutated gene ( DRN/ESR1 ), which encodes an AP2/ERF protein, is expressed in a subdomain of meristem stem cells, in lateral organ anlagen, and transiently in the distal domain of organ primordia. During the development of drn-D mutants, expression of the homeobox gene SHOOTMERISTEMLESS is downregulated and later reactivated in an altered domain. In addition, we found increased expression of CLAVATA3 and WUSCHEL , two genes that antagonistically regulate stem cell fate in meristems. These findings suggest that the DRN/ESR1 gene product is involved in the regulation of gene expression patterns in meristems. Furthermore, specific misexpression of DRN in meristem stem cells affects organ polarity and outgrowth in the meristem periphery, indicating that DRN/ESR1 itself, or a process regulated by DRN/ESR1 , can act non-cell-autonomously. We elaborate on the role of DRN/ESR1 in meristem and organ development and discuss its possible role in the process of shoot regeneration.

Aging in Legume Symbiosis. A Molecular View on Nodule Senescence in Medicago truncatula

“…Regulatory genes in this cluster could be part of signal transduction pathways triggered during the very initial stages and therefore could be important targets for future functional research. In this early cluster, two genes code for transcription factors belonging to the APETALA/ETHYLENE RESPONSE FACTOR (AP2/ERF) family known to be involved in developmental as well as disease resistance and stress responses (Kirch et al, 2003;Gutterson and Reuber, 2004;Yi et al, 2004). Interestingly, in this early cluster, a tag is present that is homologous to genes encoding abscisic acid-insensitive/viviparousrelated transcription factors and is characterized by an AP2/ERF and B3 DNA-binding domain, which are thus far unique for plants (Kagaya et al, 1999) and without obvious function.…”

WIND1 Promotes Shoot Regeneration through Transcriptional Activation of ENHANCER OF SHOOT REGENERATION1 in Arabidopsis

“…To explore the wound-induced expression of the ESR1 gene in planta, we examined the pattern of its promoter activity using Pro DRN/ESR1 :GUS lines, referred to hereafter as Pro ESR1 :GUS, in which the expression of the GUS gene is driven by the promoter of ESR1 (Kirch et al, 2003). As expected, the promoter activity of ESR1 is not detected in intact leaf explants, but its activity is induced locally at wound sites ( Figure 1B).…”

“…This is interesting, since ESR1 expression is restricted to the shoot apical meristem and leaf primordia during normal development (Kirch et al, 2003) and its overexpression confers increased shoot regenerative capacity in tissue culture (Banno et al, 2001). To validate this observation, we compared the level of ESR1 expression between 14-d-old wild-type seedlings and 35S: WIND1 callus.…”

“…To validate this further, we generated double transgenic lines between WIND1-SRDX and esr1/drn-D gain-offunction mutants, referred to hereafter as esr1-D, in which the expression of ESR1 is ectopically activated by the 35S promoter (Kirch et al, 2003), and tested whether ectopic expression of ESR1 in WIND1-SRDX plants was sufficient to rescue defects in wound-induced callus formation. As shown in Figures 4A and 4B, WIND1-SRDX leaf explants, cultured on MS medium, display strong defects in callus formation, producing only a very small mass of cells at wound sites.…”

“…A cluster of CUC2-expressing cells continues to proliferate to form promeristems, in which polarized expression of the auxin transporter PIN-FORMED1 and another meristem regulator SHOOT MERISTEMLESS (STM) further organizes the formation of functional shoot meristem. Previous studies have also identified several other regulators, such as ENHANCER OF SHOOT REGENERATION1/DORNRÖSCHEN (ESR1/DRN), ESR2/DRN-LIKE (DRNL), and RAP2.6L, that contribute to shoot regeneration in vitro (Banno et al, 2001;Kirch et al, 2003;Che et al, 2006). An early study showed that overexpression of ESR1 promotes shoot regeneration without or at low doses of exogenous cytokinin (Banno et al, 2001).…”