Hidden functional complexity in the flora of an early land ecosystem.

The first land ecosystems were composed of organisms considered simple in nature, yet the morphological diversity of their flora was extraordinary. The biological significance of this diversity remains a mystery largely due to the absence of feasible study approaches. To study the functional biology of Early Devonian flora, we have reconstructed extinct plants from fossilised remains in silico. We explored the morphological diversity of sporangia in relation to their mechanical properties using finite element method. Our approach highlights the impact of sporangia morphology on spore dispersal and adaptation. We discovered previously unidentified innovations among early land plants, discussing how different species might have opted for different spore dispersal strategies. We present examples of convergent evolution for turgor pressure resistance, achieved by homogenisation of stress in spherical sporangia and by torquing force in Tortilicaulis-like specimens. In addition, we show a potential mechanism for stress-assisted sporangium rupture. Our study reveals the deceptive complexity of this seemingly simple group of organisms. We leveraged the quantitative nature of our approach and constructed a fitness landscape to understand the different ecological niches present in the Early Devonian Welsh Borderland flora. By connecting morphology to functional biology, these findings facilitate a deeper understanding of the diversity of early land plants and their place within their ecosystem.

Meeting report - Cell size and growth: from single cells to the tree of life.

In April 2022, The Company of Biologists hosted their first post-pandemic in-person Workshop at Buxted Park Country House in the Sussex countryside. The Workshop, entitled 'Cell size and growth: from single cells to the tree of life', gathered a small group of early-career and senior researchers with expertise in cell size spanning a broad range of organisms, including bacteria, yeast, animal cells, embryos and plants, and working in fields from cell biology to ecology and evolutionary biology. The programme made ample room for fruitful discussions and provided a much-needed opportunity to discuss the most recent findings relating to the regulation of cell size and growth, identify the emerging challenges for the field, and build a community after the pandemic.

Cell size controlled in plants using DNA content as an internal scale.

How eukaryotic cells assess and maintain sizes specific for their species and cell type remains unclear. We show that in the Arabidopsis shoot stem cell niche, cell size variability caused by asymmetric divisions is corrected by adjusting the growth period before DNA synthesis. KIP-related protein 4 (KRP4) inhibits progression to DNA synthesis and associates with mitotic chromosomes. The F BOX-LIKE 17 (FBL17) protein removes excess KRP4. Consequently, daughter cells are born with comparable amounts of KRP4. Inhibitor dilution models predicted that KRP4 inherited through chromatin would robustly regulate size, whereas inheritance of excess free KRP4 would disrupt size homeostasis, as confirmed by mutant analyses. We propose that a cell cycle regulator, stabilized by association with mitotic chromosomes, reads DNA content as a cell size-independent scale.

Cell Size Control in Plants.

The genetic control of the characteristic cell sizes of different species and tissues is a long-standing enigma. Plants are convenient for studying this question in a multicellular context, as their cells do not move and are easily tracked and measured from organ initiation in the meristems to subsequent morphogenesis and differentiation. In this article, we discuss cell size control in plants compared with other organisms. As seen from yeast cells to mammalian cells, size homeostasis is maintained cell autonomously in the shoot meristem. In developing organs, vacuolization contributes to cell size heterogeneity and may resolve conflicts between growth control at the cellular and organ levels. Molecular mechanisms for cell size control have implications for how cell size responds to changes in ploidy, which are particularly important in plant development and evolution. We also discuss comparatively the functional consequences of cell size and their potential repercussions at higher scales, including genome evolution.

Small RNAs: Big Impact on Plant Development.

While the role of proteins in determining cell identity has been extensively studied, the contribution of small noncoding RNA molecules such as miRNAs and siRNAs has been also recognised. miRNAs bind to complementary sites in target mRNA molecules to trigger the degradation or translational inhibition of those targets. Recent studies have revealed that miRNAs play pivotal roles in key developmental processes such as patterning of the embryo, meristem, leaf, and flower. Furthermore, these miRNAs have been recruited throughout plant evolution into pathways that create diverse plant organ forms and shapes. This review focuses on the roles of miRNAs in establishing plant cell identity during key plant development processes and creating morphological diversity during plant evolution.