Plants optimize carbon assimilation while limiting water loss by adjusting stomatal aperture. In grasses, a developmental innovation-the addition of subsidiary cells (SCs) flanking two dumbbell-shaped guard cells (GCs)-is linked to improved stomatal physiology. Here, we identify a transcription factor necessary and sufficient for SC formation in the wheat relative Unexpectedly, the transcription factor is an ortholog of the stomatal regulator, which defines GC precursor fate in The novel role of in specifying lateral SCs appears linked to its acquisition of cell-to-cell mobility in Physiological analyses on SC-less plants experimentally support classic hypotheses that SCs permit greater stomatal responsiveness and larger range of pore apertures. Manipulation of SC formation and function in crops, therefore, may be an effective approach to enhance plant performance.

Stomata, epidermal valves facilitating plant-atmosphere gas exchange, represent a powerful model for understanding cell fate and pattern in plants. Core basic helix-loop-helix (bHLH) transcription factors regulating stomatal development were identified in Arabidopsis, but this dicot's developmental pattern and stomatal morphology represent only one of many possibilities in nature. Here, using unbiased forward genetic screens, followed by analysis of reporters and engineered mutants, we show that stomatal initiation in the grass Brachypodium distachyon uses orthologs of stomatal regulators known from Arabidopsis but that the function and behavior of individual genes, the relationships among genes, and the regulation of their protein products have diverged. Our results highlight ways in which a kernel of conserved genes may be alternatively wired to produce diversity in patterning and morphology and suggest that the stomatal transcription factor module is a prime target for breeding or genome modification to improve plant productivity.stomatal development | bHLH transcription factor | Brachypodium | grass S tomata are valves on the surface of plants with central roles in gas exchange and biosphere productivity. Stomata are both ancientthey appear on 400 million-year-old fossils-and nearly ubiquitously found in extant land plants. The diversity of stomatal morphologies and patterned distributions across different plant families coupled with rapidly advancing functional genomic resources offers a powerful opportunity to follow morphological innovation and gene regulatory network evolution simultaneously. In most plants, stomata consist of two kidney-shaped epidermal guard cells (GCs) surrounding a pore (Fig. 1A). Grass stomatal morphology is unique, featuring dumbbell-shaped GCs flanked by subsidiary cells (SCs) (Fig. 1A), and physiological measurements suggest this derived form is more efficient (1). The distribution of stomata on leaves is also species specific. Dicots such as Arabidopsis display a scattered distribution, with avoidance of direct contact being the most basic patterning rule; dispersed stem cell-like stomatal precursors divide throughout the leaf to produce this pattern and promote the typical "broadleaf" or radial growth characteristic of these plants (Fig. 1A). Grasses, in contrast, generate stomata, which are always oriented in the same direction, from specific cell files. These stomatal lineage files are established in a single zone at the leaf base with differentiation proceeding in a linear gradient toward the tip (Fig. 1A).Our understanding of the genetic underpinnings of stomatal fate and pattern is derived mostly from studies in the dicot Arabidopsis where the group Ia basic helix-loop-helix (bHLH) transcription factors SPEECHLESS (AtSPCH), AtMUTE, and AtFAMA establish stomatal lineage identity, regulate the transition to terminal precursor fate, and promote the differentiation of GCs, respectively (2-4). The function of these stage-specific factors requires heterodimerization with one of ...

Trogocytosis is part of an emerging, exciting theme of cell-cell interactions both within and between species, and it is relevant to host-pathogen interactions in many different contexts. Trogocytosis is a process in which one cell physically extracts and ingests “bites” of cellular material from another cell. It was first described in eukaryotic microbes, where it was uncovered as a mechanism by which amoebae kill cells. Trogocytosis is potentially a fundamental form of eukaryotic cell-cell interaction, since it also occurs in multicellular organisms, where it has functions in the immune system, in the central nervous system, and during development. There are numerous scenarios in which trogocytosis occurs and an ever-evolving list of functions associated with this process. Many aspects of trogocytosis are relevant to microbial pathogenesis. It was recently discovered that immune cells perform trogocytosis to kill Trichomonas vaginalis parasites. Additionally, through trogocytosis, Entamoeba histolytica acquires and displays human cell membrane proteins, enabling immune evasion. Intracellular bacteria seem to exploit host cell trogocytosis, since they can use it to spread from cell to cell. Thus, a picture is emerging in which trogocytosis plays critical roles in normal physiology, infection, and disease.