A transposon-based activation-tagging population in Arabidopsis thaliana (TAMARA) and its application in the identification of dominant developmental and metabolic mutations

AbstractA population of 9471 stable activation-tagged lines was generated by transposable element mediated activation tagging mutagenesis in Arabidopsis (TAMARA) using the maize En/Spm transposon system. Based on DNA gel blot and flanking sequence analysis, this population contains approximately 6000 independent transposon insertions. A greenhouse-based screen identified six dominant or semi-dominant activation tagged mutants with obvious developmental alterations, among these a new pistillata mutant allele. In addition, a subset of 1500 lines was screened by a HPLC based high-throughput method for dominant activation tagged mutants with enhanced contents of phenolic compounds. One dominant activation tagged mutant (hpc1-1D) was isolated showing accumulation of a particular compound due to the upregulation of an R2R3-MYB transcription factor

The intrinsic chaperone network of Arabidopsis stem cells confers protection against proteotoxic stress

The biological purpose of plant stem cells is to maintain themselves while providing new pools of differentiated cells that form organs and rejuvenate or replace damaged tissues. Protein homeostasis or proteostasis is required for cell function and viability. However, the link between proteostasis and plant stem cell identity remains unknown. In contrast to their differentiated counterparts, we find that root stem cells can prevent the accumulation of aggregated proteins even under proteotoxic stress conditions such as heat stress or proteasome inhibition. Notably, root stem cells exhibit enhanced expression of distinct chaperones that maintain proteome integrity. Particularly, intrinsic high levels of the T-complex protein-1 ring complex/chaperonin containing TCP1 (TRiC/CCT) complex determine stem cell maintenance and their remarkable ability to suppress protein aggregation. Overexpression of CCT8, a key activator of TRiC/CCT assembly, is sufficient to ameliorate protein aggregation in differentiated cells and confer resistance to proteotoxic stress in plants. Taken together, our results indicate that enhanced proteostasis mechanisms in stem cells could be an important requirement for plants to persist under extreme environmental conditions and reach extreme long ages. Thus, proteostasis of stem cells can provide insights to design and breed plants tolerant to environmental challenges caused by the climate change

Transcription of the WUSCHEL-RELATED HOMEOBOX 4 gene in Arabidopsis thaliana

Phylogenetic shadowing and chromatin accessibility data suggested that essential regulatory elements are absent in the 2.9 kb immediate upstream region of the published WOX4(pro)::YFP cambium marker. Inclusion of an additional 6.3 kb of upstream promoter sequence and confocal imaging with different fluorophores in transgenic Arabidopsis lines revealed a much wider cell-type-specific expression pattern in parenchymous cells of the aerial plant body. The previously demonstrated activity of the WOX4(pro)::YFP marker in the cambium of vascular strands in the young Arabidopsis inflorescence stem depicts only sectors of a circular subcortical layer of parenchymous AtWOX4-positive cells. Transcription starts in subepidermal cells within the inflorescence apex in a phyllotactic pattern and extends into successively branching lateral organs, which are connected via small tube-like domains of AtWOX4-expressing cells with the circular subcortical parenchymal layer that extends basipetally down the stem. AtWOX4 expression is most dynamic in leaves, where promoter activity is observed transiently at the adaxial side of the lamina and remains detectable later in the palisade parenchyma, although at a weaker level than in the vasculature. In the root the extended AtWOX4 promoter is active through the proximal root meristem, i.e. in the quiescent centre (QC) and its surrounding initials, a pattern that is broader than transcription of its stem cell promoting relative AtWOX5 in the QC. Outside the proximal meristem AtWOX4 transcription is observed in upper cell layers of the columella root cap beneath or above within the stele in proto- and metaxylem cells, in a ribbon-type pattern which divides the central cylinder in two equal halves. This xylem-specific expression it the root stele relates to established AtWOX4 activity in xylem parenchyma specificity within vascular bundles of the stem

Stem Cell Fate versus Differentiation: the Missing Link

The shoot apical meristem provides a microenvironment that ensures stem cell fate and proliferation via homeostasis between WUSCHEL (WUS) activity and CLAVATA signalling. New data from maize and arabidopsis reveal that an evolutionarily conserved signal deriving from primordium cells links WUS transcription to the morphogenetic programme

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

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