Biology subjects

Clark, F. K.

Publications and source records attributed to Clark, F. K..

5 recordsLinked to original sources

bioRxiv2026

Stomatal patterning is shaped by the interplay with giant cell patterning in Arabidopsis

In developing tissues, cells differentiate into distinct cell types and form complex spatial patterns. How distinct patterning systems interact during tissue growth to shape tissue composition and spatial organization remains poorly understood. Here, we investigate this question in the abaxial leaf epidermis of Arabidopsis thaliana, in which the same pool of progenitor cells gives rise to stomata, pavement cells, and giant cells. Using a quantitative approach combining Euclidean and network-based spatial analysis, we show that stomatal number and density are robust to reduced endoreduplication, whereas forced endoreduplication actively competes with the stomatal lineage to reduce stomatal number. Furthermore, we show that the stomatal spatial pattern is also shaped by the broader tissue context such as cell growth, cell division, and giant cell patterning, with distinct consequences for stomatal spatial distribution and cellular arrangement. Our results highlight that the interplay between patterning systems must be considered to understand how tissue organization is established.

plant biology↗

bioRxiv2024

The receptor-like kinase ALE2 promotes giant cell formation in the sepal epidermis

During sepal development in Arabidopsis thaliana, epidermal pavement cells differentiate into small cells and large, highly endoreduplicated giant cells. While the placement of giant cells differs between sepals, the number of giant cells is fairly consistent. The HD-ZIP class IV transcription factor ATML1 has been found to promote giant cell formation. ATML1 protein fluctuates within epidermal nuclei of developing sepals and high ATML1 concentrations reached in the G2 phase of the cell cycle strongly correlates with giant cell fate specification. A genetic screen for reduced giant cell number identified the receptor-like kinase ABNORMAL LEAF SHAPE2 (ALE2) as being important for giant cell formation. We find that ALE2 functions genetically upstream of ATML1 in promoting the formation of giant cells. We observe that nuclear-localized mCitrine-ATML1 fluctuates in ale2 mutants much as it does in wild type and, importantly, nuclear mCitrine-ATML1 reaches similarly high peak concentrations in ale2-1 mutants as in wild type. This indicates that ALE2 functions upstream of ATML1 by affecting protein activity rather than gene expression or protein degradation. One function of ATML1 is to promote transcription of the CDK inhibitor LGO. We find that LGO transcription is delayed and decreased in ale2-1 mutants as compared to wild-type plants, consistent with ATML1 having impaired protein function in ale2 mutants. Overall, we find that the receptor-like kinase ALE2 is necessary to sensitize cells of the developing sepal epidermis to fluctuations of the transcription factor ATML1.

plant biology↗

bioRxiv2024

A common pathway controls cell size in the sepal and leaf epidermis leading to a non-random pattern of giant cells

Arabidopsis leaf epidermal cells have a wide range of sizes and ploidies, but the mechanisms patterning their size and spatial distribution remain unclear. Here, we show that the same genetic pathway creating giant cells in sepals also regulates cell size in the leaf epidermis, leading to the formation of giant cells. In both sepals and leaves, giant cells are scattered among smaller cells; therefore, we asked whether their spatial arrangement is random. By comparing sepal and leaf epidermises with computationally generated randomized tissues we show that the giant cell pattern becomes less random across the epidermis as the cells surrounding giant cells divide, leading to clustered patterns in mature tissues. Our cell-autonomous and stochastic computational model reproduces the giant cell organization, suggesting that random giant cell initiation together with the divisions of surrounding cells lead to the observed clustered pattern. These findings reveal that cell-size patterning is developmentally regulated by common mechanisms in leaves and sepals, and the spatial pattern of giant cells emerges from the interplay between stochastic cell- autonomous gene expression and tissue growth.

plant biology↗

bioRxiv2024

The transcription factor ATML1 maintains giant cell identity by inducing synthesis of its own (very) long-chain fatty acid-containing ligands

During development, cells not only adopt specialized identities but also maintain those identities. Endoreduplication is thought to maintain cell identity. High concentrations of ARABIDOPSIS THALIANA MERISTEM LAYER1 (ATML1) specify giant cell identity and induce endoreduplication in sepals. How different concentrations of ATML1 can specify different identities remains unclear. Here, we show that high concentrations of ATML1 induce the biosynthesis of both long-chain and very long-chain fatty acids (LCFAs/VLCFAs), and these fatty acids are required for the maintenance of giant cell identity. Inhibition of VLCFA biosynthesis causes endoreduplicated giant cells to resume division and lose their identity, indicating that endoreduplication is not sufficient to maintain cell identity. Structural predictions suggest that LCFA-containing lipids bind to the START domain 2 of ATML1, causing ATML1 dimerization and its auto-activation. Our data and modeling imply that ATML1 induces biosynthesis of its own lipid ligands in a positive feedback loop, shedding light on the intricate network dynamics that specify and maintain giant cell identity. Teaser: Endoreduplicated cells in Arabidopsis thaliana sepals divide and de-differentiate in the absence of VLCFA biosynthesis.

plant biology↗

bioRxiv2023

Robust organ size in Arabidopsis is primarily governed by cell growth rather than cell division patterns

Organ sizes and shapes are highly reproducible, or robust, within a species and individuals. Arabidopsis thaliana sepals, which are the leaf-like organs that enclose flower buds, have consistent size and shape, which indicates robust development. Counterintuitively, variability in cell growth rate over time and between cells facilitates robust development because cumulative cell growth averages to a uniform rate. Here we investigate how sepal morphogenesis is robust to changes in cell division but not robust to changes in cell growth variability. We live image and quantitatively compare the development of sepals with increased or decreased cell division rate (lgo mutant and LGO overexpression, respectively), a mutant with altered cell growth variability (ftsh4), and double mutants combining these. We find that robustness is preserved when cell division rate changes because there is no change in the spatial pattern of growth. Meanwhile when robustness is lost in ftsh4 mutants, cell growth accumulates unevenly, and cells have disorganized growth directions. Thus, we demonstrate in vivo that both cell growth rate and direction average in robust development, preserving robustness despite changes in cell division. Summary statementRobust sepal development is preserved despite changes in cell division rate and is characterized by spatiotemporal averaging of heterogeneity in cell growth rate and direction.

plant biology↗