Biology subjects

Bergmann, D. C.

Publications and source records attributed to Bergmann, D. C..

4 recordsLinked to original sources

bioRxiv2018

SOL1 and SOL2 Regulate Fate Transition and Cell Divisions in the Arabidopsis Stomatal Lineage

In the stomatal lineage, cells make fate transitions from asymmetrically dividing and self-renewing meristemoids, to commitment to the guard mother cell identity, and finally though a single division to create mature, post-mitotic stomatal guard cells. Flexibility in the stomatal lineage allows plants to alter leaf size and stomatal density in response to environmental conditions; however, transitions must be clean and unidirectional in order to produce functional and correctly patterned stomata. Among direct transcriptional targets of the stomatal initiating factor, SPEECHLESS, we found a pair of genes, SOL1 and SOL2, required for effective transitions in the lineage. Here we show that these two genes, which are homologues of the LIN54 DNA-binding components of the mammalian DREAM complex, are expressed in a cell cycle dependent manner and regulate cell fate and division properties in the self-renewing early lineage. In the terminal division of the stomatal lineage, however, these two proteins appear to act in opposition to their closest paralogue, TSO1, revealing complexity in the gene family may enable customization of cell divisions in coordination with development.

developmental biology↗

bioRxiv2018

Conservation and Divergence of YODA MAPKKK Function in Regulation of Grass Epidermal Patterning

All multicellular organisms must properly pattern cell types to generate functional tissues and organs. The organized and predictable cell lineages of the Brachypodium leaf enabled us to characterize the role of the MAPK kinase kinase gene BdYODA1 in regulating asymmetric cell divisions. We find that YODA genes promote normal stomatal spacing patterns in both Arabidopsis and Brachypodium, despite species-specific differences in those patterns. Using lineage tracing and cell fate markers, we show that, unexpectedly, patterning defects in bdyoda1 mutants do not arise from faulty physical asymmetry in cell divisions but rather from improper enforcement of alternative cellular fates after division. These cross-species comparisons allow us to refine our interpretations of MAPK activities during plant asymmetric cell divisions.\n\nSummary StatementAnalysis of Brachypodium leaf epidermis development reveals that the MAPKKK, BdYODA1, regulates asymmetric divisions by enforcing resultant cell fates rather than driving initial physical asymmetries.

plant biology↗

bioRxiv2017

Lineage and stage-specific expressed CYCD7;1 coordinates the single symmetric division that creates stomatal guard cells

Plants, with cells fixed in place by rigid walls, often utilize spatial and temporally distinct cell division programs to organize and maintain organs. This leads to the question of how developmental regulators interact with the cell cycle machinery to link cell division events with particular developmental trajectories. In Arabidopsis leaves, the development of stomata, two-celled epidermal valves that mediate plant-atmosphere gas exchange, relies on a series of oriented stem-cell-like asymmetric divisions followed by a single symmetric division. The stomatal lineage is embedded in a tissue whose cells transition from proliferation to post-mitotic differentiation earlier, necessitating stomatal lineage-specific factors to prolong competence to divide. We show that the D-type cyclin, CYCD7;1 is specifically expressed just prior to the symmetric guard-cell forming division, and that it is limiting for this division. Further, we find that CYCD7;1 is capable of promoting divisions in multiple contexts, likely through RBR-dependent promotion of the G1/S transition, but that CYCD7;1 is regulated at the transcriptional level by cell-type specific transcription factors that confine its expression to the appropriate developmental window.

plant biology↗

bioRxiv2017

Dissection of MAPK signaling specificity through protein engineering in a developmental context

Mitogen-activated protein kinases (MAPK) signaling affects many processes, some of which have different outcomes in the same cell. In Arabidopsis, activation of a MAPK cascade consisting of YODA, MKK4/5 and MPK3/6 inhibits early stages of stomatal developmental, but this ability is lost at the latest stage when guard mother cells (GMCs) transition to guard cells (GCs). Rather than downregulating cascade components, stomatal precursors must have a mechanism to prevent late stage inhibition because the same MKKs and MPKs mediate other physiological responses. Here, we artificially activated the MAPK cascade using MKK7, another MKK that can modulate stomatal development, and found that inhibition of stomatal development is still possible in GMCs. This suggests that MKK4/5, but not MKK7, are specifically prevented from inhibiting stomatal development. To identify regions of MKKs responsible for cell-type specific regulation, we used a domain swap approach with MKK7 and a battery of in vitro and in vivo kinase assays. We found that N-terminal regions of MKK5 and MKK7 establish specific signal-to-output connections like they do in other organisms, but they do so in combination with previously undescribed modules in the C-terminus. One of these modules encodes the GMC-specific regulation of MKK5, that when swapped with MKK7s, allows MKK5 to mediate robust inhibition of late stomatal development. Because MKK structure is conserved across species, the identification of new MKK specificity modules and signaling rules furthers our understanding of how eukaryotes create specificity in complex biological systems.

plant biology↗