Variability and constancy in cellular growth of Arabidopsis sepals

Abstract

Growth of tissues is highly reproducible; yet, growth of individual cells in a tissue is highly variable, and neighboring cells can grow at different rates. We analyzed the growth of epidermal cell lineages in the Arabidopsis (Arabidopsis thaliana) sepal to determine how the growth curves of individual cell lineages relate to one another in a developing tissue. To identify underlying growth trends, we developed a continuous displacement field to predict spatially averaged growth rates. We showed that this displacement field accurately describes the growth of sepal cell lineages and reveals underlying trends within the variability of in vivo cellular growth. We found that the tissue, individual cell lineages, and cell walls all exhibit growth rates that are initially low, accelerate to a maximum, and decrease again. Accordingly, these growth curves can be represented by sigmoid functions. We examined the relationships among the cell lineage growth curves and surprisingly found that all lineages reach the same maximum growth rate relative to their size. However, the cell lineages are not synchronized; each cell lineage reaches this same maximum relative growth rate but at different times. The heterogeneity in observed growth results from shifting the same underlying sigmoid curve in time and scaling by size. Thus, despite the variability in growth observed in our study and others, individual cell lineages in the developing sepal follow similarly shaped growth curves.

CUTIN SYNTHASE 2 Maintains Progressively Developing Cuticular Ridges in Arabidopsis Sepals

“…Here, we characterize the dynamic formation of cuticular ridges on the Arabidopsis floral organ epidermis in a developmental context. We use the sepal as a model system because it is the outermost floral organ, which is accessible for live imaging and cellular growth analysis (Roeder et al, 2010(Roeder et al, , 2012Qu et al, 2014;Tauriello et al, 2015;Hong et al, 2016). Our results show that cuticular ridge formation proceeds from the tip to the base of the sepal, coincident with the wave of cellular maturation typified by the cessation of cell division and transition to slow cell growth.…”

Ploidy and Size at Multiple Scales in the Arabidopsis Sepal

“…diploid plants have ploidy between 2C and 32C and vary ∼40fold in length (Roeder et al, 2010) ( Figure 1D). Live imaging of Arabidopsis sepal pavement cells has shown that endoreduplicating cells grow at the same relative rate, on average, as their dividing neighbors (Tauriello et al, 2015); in essence, endoreduplicated cells are larger because they grow without being halved by division (Roeder et al, 2010). Endopolyploidy has also been linked to cell fate: nascent trichomes in which endoreduplication is blocked often lose their identity (Bramsiepe et al, 2010), and pavement cells differ in gene expression based on their level of endopolyploidy (Roeder et al, 2012;Schwarz and Roeder, 2016).…”

Fluctuations of the transcription factor ATML1 generate the pattern of giant cells in the Arabidopsis sepal

“…During the development of Arabidopsis thaliana ’s outmost floral organ, the sepal, equivalent epidermal cells in the primordium differentiate to produce a scattered pattern of giant cells that are interspersed between smaller cells (Figure 1A–F; Roeder et al, 2010, 2012; Tauriello et al, 2015). The sepal is a useful model system because the giant cell patterning process can be live imaged from the earliest stages of initiation through giant cell differentiation.…”