A spatiotemporal molecular switch governs plant asymmetric cell division

Changes in hemicellulose metabolism in banana peel during fruit development and ripening

Hemicellulose is key in determining the fate of plant cell wall in almost all growth and developmental stages. Nevertheless, there is limited knowledge regarding its involvement in the development and ripening of banana fruit. This study investigated changes in the temporal-spatial distribution of various hemicellulose components, hemicellulose content, activities of the main hydrolysis enzymes, and transcription level of the main hemicellulose-related gene families in banana peels. Both hemicellulose and xylan contents were positively correlated to the fruit firmness observed in our previous study. On the contrary, the xylanase activity was negatively correlated to xylan content and the fruit firmness. The vascular bundle cells, phloem, and cortex of bananas are abundant in xyloglucan, xylan, and mannan contents. Interestingly, the changes in the signal intensity of the CCRC-M104 antibody recognizing non-XXXG type xyloglucan are positively correlated to hemicellulose content. According to RNA-Seq analysis, xyloglucan and xylan-related genes were highly active in the early stages of growth, and the expression of MaMANs and MaXYNs increased as the fruit ripened. The abundance of plant hormonal and growth-responsive cis-acting elements was detected in the 2 kb upstream region of hemicellulose-related gene families. Interaction between hemicellulose and cell wall-specific proteins and MaKCBP1/2, MaCKG1, and MaHKL1 was found. The findings shed light on cell wall hemicellulose's role in banana fruit development and ripening, which could improve nutrition, flavor, and reduce postharvest fruit losses.

A multifaceted kinase axis regulates plant organ abscission through conserved signaling mechanisms

Plants have evolved mechanisms to abscise organs as they develop or when exposed to unfavorable conditions.1 Uncontrolled abscission of petals, fruits, or leaves can impair agricultural productivity.2,3,4,5 Despite its importance for abscission progression, our understanding of the IDA signaling pathway and its regulation remains incomplete. IDA is secreted to the apoplast, where it is perceived by the receptors HAESA (HAE) and HAESA-LIKE2 (HSL2) and somatic embryogenesis receptor kinase (SERK) co-receptors.6,7,8,9 These plasma membrane receptors activate an intracellular cascade of mitogen-activated protein kinases (MAPKs) by an unknown mechanism.10,11,12 Here, we characterize brassinosteroid signaling kinases (BSKs) as regulators of floral organ abscission in Arabidopsis. BSK1 localizes to the plasma membrane of abscission zone cells, where it interacts with HAESA receptors to regulate abscission. Furthermore, we demonstrate that YODA (YDA) has a leading role among other MAPKKKs in controlling abscission downstream of the HAESA/BSK complex. This kinase axis, comprising a leucine-rich repeat receptor kinase, a BSK, and an MAPKKK, is known to regulate stomatal patterning, early embryo development, and immunity.10,13,14,15,16 How specific cellular responses are obtained despite signaling through common effectors is not well understood. We show that the identified abscission-promoting allele of BSK1 also enhances receptor signaling in other BSK-mediated pathways, suggesting conservation of signaling mechanisms. Furthermore, we provide genetic evidence supporting independence of BSK1 function from its kinase activity in several developmental processes. Together, our findings suggest that BSK1 facilitates signaling between plasma membrane receptor kinases and MAPKKKs via conserved mechanisms across multiple facets of plant development.

Regulation of stomatal development by epidermal, subepidermal and long-distance signals

Plant leaves consist of three layers, including epidermis, mesophyll and vascular tissues. Their development is meticulously orchestrated. Stomata are the specified structures on the epidermis for uptake of carbon dioxide (CO2) while release of water vapour and oxygen (O2), and thus play essential roles in regulation of plant photosynthesis and water use efficiency. To function efficiently, stomatal formation must coordinate with the development of other epidermal cell types, such as pavement cell and trichome, and tissues of other layers, such as mesophyll and leaf vein. This review summarizes the regulation of stomatal development in three dimensions (3D). In the epidermis, specific stomatal transcription factors determine cell fate transitions and also activate a ligand-receptor- MITOGEN-ACTIVATED PROTEIN KINASE (MAPK) signaling for ensuring proper stomatal density and patterning. This forms the core regulation network of stomatal development, which integrates various environmental cues and phytohormone signals to modulate stomatal production. Under the epidermis, mesophyll, endodermis of hypocotyl and inflorescence stem, and veins in grasses secrete mobile signals to influence stomatal formation in the epidermis. In addition, long-distance signals which may include phytohormones, RNAs, peptides and proteins originated from other plant organs modulate stomatal development, enabling plants to systematically adapt to the ever changing environment.

The stomatal fates: Understanding initiation and enforcement of stomatal cell fate transitions

In the stomatal lineage, repeated arcs of initiation, stem-cell proliferation, and terminal cell fate commitment are displayed on the surface of aerial organs. Over the past two decades, the core transcription and signaling elements that guide cell divisions, patterning, and fate transitions were defined. Here we highlight recent work that extends the core using a variety of cutting-edge techniques in different plant species. New work has discovered transcriptional circuits that initiate and reinforce stomatal fate transitions, while also enabling the lineage to interpret and respond to environmental inputs. Recent developments show that some key stomatal factors are more flexible or potentially even interchangeable, opening up avenues to explore stomatal fates and regulatory networks.

Membrane microdomains: Structural and signaling platforms for establishing membrane polarity

Cell polarity results from the asymmetric distribution of cellular structures, molecules, and functions. Polarity is a fundamental cellular trait that can determine the orientation of cell division, the formation of particular cell shapes, and ultimately the development of a multicellular body. To maintain the distinct asymmetric distribution of proteins and lipids in cellular membranes, plant cells have developed complex trafficking and regulatory mechanisms. Major advances have been made in our understanding of how membrane microdomains influence the asymmetric distribution of proteins and lipids. In this review, we first give an overview of cell polarity. Next, we discuss current knowledge concerning membrane microdomains and their roles as structural and signaling platforms to establish and maintain membrane polarity, with a special focus on the asymmetric distribution of proteins and lipids, and advanced microscopy techniques to observe and characterize membrane microdomains. Finally, we review recent advances regarding membrane trafficking in cell polarity establishment and how the balance between exocytosis and endocytosis affects membrane polarity.

Cell type-specific attenuation of brassinosteroid signaling precedes stomatal asymmetric cell division

In Arabidopsis thaliana, brassinosteroid (BR) signaling and stomatal development are connected through the SHAGGY/GSK3-like kinase BR INSENSITIVE2 (BIN2). BIN2 is a key negative regulator of BR signaling but it plays a dual role in stomatal development. BIN2 promotes or restricts stomatal asymmetric cell division (ACD) depending on its subcellular localization, which is regulated by the stomatal lineage-specific scaffold protein POLAR. BRs inactivate BIN2, but how they govern stomatal development remains unclear. Mapping the single-cell transcriptome of stomatal lineages after triggering BR signaling with either exogenous BRs or the specific BIN2 inhibitor, bikinin, revealed that the two modes of BR signaling activation generate spatiotemporally distinct transcriptional responses. We established that BIN2 is always sensitive to the inhibitor but, when in a complex with POLAR and its closest homolog POLAR-LIKE1, it becomes protected from BR-mediated inactivation. Subsequently, BR signaling in ACD precursors is attenuated, while it remains active in epidermal cells devoid of scaffolds and undergoing differentiation. Our study demonstrates how scaffold proteins contribute to cellular signal specificity of hormonal responses in plants.

Polarizing to the challenge: New insights into polarity-mediated division orientation in plant development

Land plants depend on oriented cell divisions that specify cell identities and tissue architecture. As such, the initiation and subsequent growth of plant organs require pathways that integrate diverse systemic signals to inform division orientation. Cell polarity is one solution to this challenge, allowing cells to generate internal asymmetry both spontaneously and in response to extrinsic cues. Here, we provide an update on our understanding of how plasma membrane-associated polarity domains control division orientation in plant cells. These cortical polar domains are flexible protein platforms whose positions, dynamics, and recruited effectors can be modulated by varied signals to control cellular behavior. Several recent reviews have explored the formation and maintenance of polar domains during plant development [1-4], so we focus here on substantial advances in our understanding of polarity-mediated division orientation from the last five years to provide a current snapshot of the field and highlight areas for future exploration.

Maintaining asymmetry in cell division

Promoting asymmetric division through microtubule dynamics establishes cell fate.

Asymmetric cell division in plant development

Asymmetric cell division (ACD) is a fundamental process that generates new cell types during development in eukaryotic species. In plant development, post-embryonic organogenesis driven by ACD is universal and more important than in animals, in which organ pattern is preset during embryogenesis. Thus, plant development provides a powerful system to study molecular mechanisms underlying ACD. During the past decade, tremendous progress has been made in our understanding of the key components and mechanisms involved in this important process in plants. Here, we present an overview of how ACD is determined and regulated in multiple biological processes in plant development and compare their conservation and specificity among different model cell systems. We also summarize the molecular roles and mechanisms of the phytohormones in the regulation of plant ACD. Finally, we conclude with the overarching paradigms and principles that govern plant ACD and consider how new technologies can be exploited to fill the knowledge gaps and make new advances in the field.

Emerging roles of protein phosphorylation in regulation of stomatal development

Stomata, tiny epidermal spores, control gas exchange between plants and their external environment, thereby playing essential roles in plant development and physiology. Stomatal development requires rapid regulation of components in signaling pathways to respond flexibly to numerous intrinsic and extrinsic signals. In support of this, reversible phosphorylation, which is particularly suitable for rapid signal transduction, has been implicated in this process. This review highlights the current understanding of the essential roles of reversible phosphorylation in the regulation of stomatal development, most of which comes from the dicot Arabidopsis thaliana. Protein phosphorylation tightly controls the activity of SPEECHLESS (SPCH)-SCREAM (SCRM), the stomatal lineage switch, and the activity of several mitogen-activated protein kinases and receptor kinases upstream of SPCH-SCRM, thereby regulating stomatal cell differentiation and patterning. In addition, protein phosphorylation is involved in the establishment of cell polarity during stomatal asymmetric cell division. Finally, cyclin-dependent kinase-mediated protein phosphorylation plays essential roles in cell cycle control during stomatal development.

Protein polarization: Spatiotemporal precisions in cell division and differentiation

Specification of cell polarity is vital to normal cell growth, morphogenesis, and function. As other eukaryotes, plants generate cellular polarity that is coordinated with tissue polarity and organ axes. In development, new cell types are generated by stem-cell division and differentiation, a process often involving proteins that are polarized to cortical domains at the plasma membrane. In the past decade, pioneering work using the model plant Arabidopsis identified multiple proteins that are polarized in dividing cells to instruct divisional behaviors and/or specify cell fates. In this review, we use these polarized cell-division regulators as example to summarize key mechanisms underlying protein polarization in plant cells. Recent progress underscores that self-organizing amplification processes are commonly involved in establishing cell polarity, and cellular polarity is influenced by both tissue-level and local mechanochemical cues. In addition, protein polarization during asymmetric cell division shows a distinct feature of temporal control in the stomatal lineage. We further discuss possible coordination between protein polarization and the progression of cell cycle in this developmental context.

Deconvoluting signals downstream of growth and immune receptor kinases by phosphocodes of the BSU1 family phosphatases

Hundreds of leucine-rich repeat receptor kinases (LRR-RKs) have evolved to control diverse processes of growth, development and immunity in plants, but the mechanisms that link LRR-RKs to distinct cellular responses are not understood. Here we show that two LRR-RKs, the brassinosteroid hormone receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1) and the flagellin receptor FLAGELLIN SENSING 2 (FLS2), regulate downstream glycogen synthase kinase 3 (GSK3) and mitogen-activated protein (MAP) kinases, respectively, through phosphocoding of the BRI1-SUPPRESSOR1 (BSU1) phosphatase. BSU1 was previously identified as a component that inactivates GSK3s in the BRI1 pathway. We surprisingly found that the loss of the BSU1 family phosphatases activates effector-triggered immunity and impairs flagellin-triggered MAP kinase activation and immunity. The flagellin-activated BOTRYTIS-INDUCED KINASE 1 (BIK1) phosphorylates BSU1 at serine 251. Mutation of serine 251 reduces BSU1's ability to mediate flagellin-induced MAP kinase activation and immunity, but not its abilities to suppress effector-triggered immunity and interact with GSK3, which is enhanced through the phosphorylation of BSU1 at serine 764 upon brassinosteroid signalling. These results demonstrate that BSU1 plays an essential role in immunity and transduces brassinosteroid-BRI1 and flagellin-FLS2 signals using different phosphorylation sites. Our study illustrates that phosphocoding in shared downstream components provides signalling specificities for diverse plant receptor kinases.

Division site determination during asymmetric cell division in plants

During development, both animals and plants exploit asymmetric cell division (ACD) to increase tissue complexity, a process that usually generates cells dissimilar in size, morphology, and fate. Plants lack the key regulators that control ACD in animals. Instead, plants have evolved two unique cytoskeletal structures to tackle this problem: the preprophase band (PPB) and phragmoplast. The assembly of the PPB and phragmoplast and their contributions to division plane orientation have been extensively studied. However, how the division plane is positioned off the cell center during asymmetric division is poorly understood. Over the past 20 years, emerging evidence points to a critical role for polarly localized membrane proteins in this process. Although many of these proteins are species- or cell type specific, and the molecular mechanism underlying division asymmetry is not fully understood, common features such as morphological changes in cells, cytoskeletal dynamics, and nuclear positioning have been observed. In this review, we provide updates on polarity establishment and nuclear positioning during ACD in plants. Together with previous findings about symmetrically dividing cells and the emerging roles of developmental cues, we aim to offer evolutionary insight into a common framework for asymmetric division-site determination and highlight directions for future work.

Dichotomy of the BSL phosphatase signaling spatially regulates MAPK components in stomatal fate determination

MAPK signaling modules play crucial roles in regulating numerous biological processes in all eukaryotic cells. How MAPK signaling specificity and strength are tightly controlled remains a major challenging question. In Arabidopsis stomatal development, the MAPKK Kinase YODA (YDA) functions at the cell periphery to inhibit stomatal production by activating MAPK 3 and 6 (MPK3/6) that directly phosphorylate stomatal fate-determining transcription factors for degradation in the nucleus. Recently, we demonstrated that BSL1, one of the four BSL protein phosphatases, localizes to the cell cortex to activate YDA, elevating MPK3/6 activity to suppress stomatal formation. Here, we showed that at the plasma membrane, all four members of BSL proteins contribute to the YDA activation. However, in the nucleus, specific BSL members (BSL2, BSL3, and BSU1) directly deactivate MPK6 to counteract the linear MAPK pathway, thereby promoting stomatal formation. Thus, the pivotal MAPK signaling in stomatal fate determination is spatially modulated by a signaling dichotomy of the BSL protein phosphatases in Arabidopsis, providing a prominent example of how MAPK activities are integrated and specified by signaling compartmentalization at the subcellular level.

Cycling in a crowd: Coordination of plant cell division, growth, and cell fate

The reiterative organogenesis that drives plant growth relies on the constant production of new cells, which remain encased by interconnected cell walls. For these reasons, plant morphogenesis strictly depends on the rate and orientation of both cell division and cell growth. Important progress has been made in recent years in understanding how cell cycle progression and the orientation of cell divisions are coordinated with cell and organ growth and with the acquisition of specialized cell fates. We review basic concepts and players in plant cell cycle and division, and then focus on their links to growth-related cues, such as metabolic state, cell size, cell geometry, and cell mechanics, and on how cell cycle progression and cell division are linked to specific cell fates. The retinoblastoma pathway has emerged as a major player in the coordination of the cell cycle with both growth and cell identity, while microtubule dynamics are central in the coordination of oriented cell divisions. Future challenges include clarifying feedbacks between growth and cell cycle progression, revealing the molecular basis of cell division orientation in response to mechanical and chemical signals, and probing the links between cell fate changes and chromatin dynamics during the cell cycle.

Cell biology of the leaf epidermis: Fate specification, morphogenesis, and coordination

As the outermost layer of plants, the epidermis serves as a critical interface between plants and the environment. During leaf development, the differentiation of specialized epidermal cell types, including stomatal guard cells, pavement cells, and trichomes, occurs simultaneously, each providing unique and pivotal functions for plant growth and survival. Decades of molecular-genetic and physiological studies have unraveled key players and hormone signaling specifying epidermal differentiation. However, most studies focus on only one cell type at a time, and how these distinct cell types coordinate as a unit is far from well-comprehended. Here we provide a review on the current knowledge of regulatory mechanisms underpinning the fate specification, differentiation, morphogenesis, and positioning of these specialized cell types. Emphasis is given to their shared developmental origins, fate flexibility, as well as cell cycle and hormonal controls. Furthermore, we discuss computational modeling approaches to integrate how mechanical properties of individual epidermal cell types and entire tissue/organ properties mutually influence each other. We hope to illuminate the underlying mechanisms coordinating the cell differentiation that ultimately generate a functional leaf epidermis.

Connected function of PRAF/RLD and GNOM in membrane trafficking controls intrinsic cell polarity in plants

Cell polarity is a fundamental feature underlying cell morphogenesis and organismal development. In the Arabidopsis stomatal lineage, the polarity protein BASL controls stomatal asymmetric cell division. However, the cellular machinery by which this intrinsic polarity site is established remains unknown. Here, we identify the PRAF/RLD proteins as BASL physical partners and mutating four PRAF members leads to defects in BASL polarization. Members of PRAF proteins are polarized in stomatal lineage cells in a BASL-dependent manner. Developmental defects of the praf mutants phenocopy those of the gnom mutants. GNOM is an activator of the conserved Arf GTPases and plays important roles in membrane trafficking. We further find PRAF physically interacts with GNOM in vitro and in vivo. Thus, we propose that the positive feedback of BASL and PRAF at the plasma membrane and the connected function of PRAF and GNOM in endosomal trafficking establish intrinsic cell polarity in the Arabidopsis stomatal lineage.

Glycogen synthase kinases in model and crop plants - From negative regulators of brassinosteroid signaling to multifaceted hubs of various signaling pathways and modulators of plant reproduction and yield

Glycogen synthase kinases, also known as SHAGGY-like Kinases (GSKs/SKs), are highly conserved serine/threonine protein kinases present both in animals and plants. Plant genomes contain multiple homologs of the GSK3 genes which participate in various biological processes. Plant GSKs/SKs, and their best known representative in Arabidopsis thaliana - Brassinosteroid Insentisive2 (BIN2/SK21) in particular, were first identified as components of the brassinosteroid (BR) signaling pathway. As phytohormones, BRs regulate a wide range of physiological processes in plants - from germination, cell division, elongation and differentiation to leaf senescence, and response to environmental stresses. The GSKs/SKs proteins belong to a group of several highly conserved components of the BR signaling which evolved early during evolution of this molecular relay. However, recent reports indicated that the GSKs/SKs proteins are also implicated in signaling pathways of other phytohormones and stress-response processes. As a consequence, the GSKs/SKs proteins became hubs of various signaling pathways and modulators of plant development and reproduction. Thus, it is very important to understand molecular mechanisms regulating activity of the GSKs/SKs proteins, but also to get insights into role of the GSKs/SKs proteins in modulation of stability and activity of various substrate proteins which participate in the numerous signaling pathways. Although elucidation of these aspects is still in progress, this review presents a comprehensive and detailed description of these processes and their implications for regulation of development, stress response, and reproduction of model and crop species. The GSKs/SKs proteins and their activity are modulated through phosphorylation and de-phosphorylation reactions which are regulated by various proteins. Importantly, both phosphorylations and de-phosphorylations may have positive and negative effects on the activity of the GSKs/SKs proteins. Additionally, the activity of the GSKs/SKs proteins is positively regulated by reactive oxygen species, whereas it is negatively regulated through ubiquitylation, deacetylation, and nitric oxide-mediated nitrosylation. On the other hand, the GSKs/SKs proteins interact with proteins representing various signaling pathways, and on the basis of the complicated network of interactions the GSKs/SKs proteins differentially regulate various physiological, developmental, stress response, and yield-related processes.

Using quantitative methods to understand leaf epidermal development

As the interface between plants and the environment, the leaf epidermis provides the first layer of protection against drought, ultraviolet light, and pathogen attack. This cell layer comprises highly coordinated and specialised cells such as stomata, pavement cells and trichomes. While much has been learned from the genetic dissection of stomatal, trichome and pavement cell formation, emerging methods in quantitative measurements that monitor cellular or tissue dynamics will allow us to further investigate cell state transitions and fate determination in leaf epidermal development. In this review, we introduce the formation of epidermal cell types in Arabidopsis and provide examples of quantitative tools to describe phenotypes in leaf research. We further focus on cellular factors involved in triggering cell fates and their quantitative measurements in mechanistic studies and biological patterning. A comprehensive understanding of how a functional leaf epidermis develops will advance the breeding of crops with improved stress tolerance.

Opposite polarity programs regulate asymmetric subsidiary cell divisions in grasses

Grass stomata recruit lateral subsidiary cells (SCs), which are key to the unique stomatal morphology and the efficient plant-atmosphere gas exchange in grasses. Subsidiary mother cells (SMCs) strongly polarise before an asymmetric division forms a SC. Yet apart from a proximal polarity module that includes PANGLOSS1 (PAN1) and guides nuclear migration, little is known regarding the developmental processes that form SCs. Here, we used comparative transcriptomics of developing wild-type and SC-less bdmute leaves in the genetic model grass Brachypodium distachyon to identify novel factors involved in SC formation. This approach revealed BdPOLAR, which forms a novel, distal polarity domain in SMCs that is opposite to the proximal PAN1 domain. Both polarity domains are required for the formative SC division yet exhibit various roles in guiding pre-mitotic nuclear migration and SMC division plane orientation, respectively. Nonetheless, the domains are linked as the proximal domain controls polarisation of the distal domain. In summary, we identified two opposing polarity domains that coordinate the SC division, a process crucial for grass stomatal physiology.

GSK3s: nodes of multilayer regulation of plant development and stress responses

Glycogen synthase kinase 3 (GSK3) family members are highly conserved serine/threonine protein kinases in eukaryotes. Unlike animals, plants have evolved with multiple homologs of GSK3s involved in a diverse array of biological processes. Emerging evidence suggests that GSK3s act as signaling hubs for integrating perception and transduction of diverse signals required for plant development and responses to abiotic and biotic cues. Here we review recent advances in understanding the molecular interactions between GSK3s and an expanding spectrum of their upstream regulators and downstream substrates in plants. We further discuss how GSK3s act as key signaling nodes of multilayer regulation of plant development and stress response through either being regulated at the post-translational level or regulating their substrates via phosphorylation.

Evolution of polarity protein BASL and the capacity for stomatal lineage asymmetric divisions

Asymmetric and oriented stem cell divisions enable the continued production of patterned tissues. The molecules that guide these divisions include several "polarity proteins" that are localized to discrete plasma membrane domains, are differentially inherited during asymmetric divisions, and whose scaffolding activities can guide division plane orientation and subsequent cell fates. In the stomatal lineages on the surfaces of plant leaves, asymmetric and oriented divisions create distinct cell types in physiologically optimized patterns. The polarity protein BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE (BASL) is a major regulator of stomatal lineage division and cell fate asymmetries in Arabidopsis, but its role in the stomatal lineages of other plants is unclear. Here, using phylogenetic and functional assays, we demonstrate that BASL is a eudicot-specific polarity protein. Dicot BASL orthologs can polarize in heterologous systems and rescue the Arabidopsis BASL mutant. The more widely distributed BASL-like proteins, although they share BASL's conserved C-terminal domain, are neither polarized nor do they function in asymmetric divisions of the stomatal lineage. Comparison of BASL protein localization and loss of function BASL phenotypes in Arabidopsis and tomato revealed previously unappreciated differences in how asymmetric cell divisions are employed for pattern formation in different species. This multi-species analysis therefore provides insight into the evolution of a unique polarity regulator and into the developmental choices available to cells as they build and pattern tissues.

Establishing asymmetry: stomatal division and differentiation in plants

In the leaf epidermis, stomatal pores allow gas exchange between plants and the environment. The production of stomatal guard cells requires the lineage cells to divide asymmetrically. In this Insight review, we describe an emerging picture of how intrinsic molecules drive stomatal asymmetric cell division in multidimensions, from transcriptional activities in the nucleus to the dynamic assembly of the polarity complex at the cell cortex. Given the significant roles of stomatal activity in plant responses to environmental changes, we incorporate recent advances in external cues feeding into the regulation of core molecular machinery required for stomatal development. The work we discuss here is mainly based on the dicot plant Arabidopsis thaliana with summaries of recent progress in the monocots.

Stomatal Lineage Control by Developmental Program and Environmental Cues

Stomata are micropores that allow plants to breathe and play a critical role in photosynthesis and nutrient uptake by regulating gas exchange and transpiration. Stomatal development, therefore, is optimized for survival and growth of the plant despite variable environmental conditions. Signaling cascades and transcriptional networks that determine the birth, proliferation, and differentiation of a stomate have been identified. These networks ensure proper stomatal patterning, density, and polarity. Environmental cues also influence stomatal development. In this review, we highlight recent findings regarding the developmental program governing cell fate and dynamics of stomatal lineage cells at the cell state- or single-cell level. We also overview the control of stomatal development by environmental cues as well as developmental plasticity associated with stomatal function and physiology. Recent advances in our understanding of stomatal development will provide a route to improving photosynthesis and water-stress resilience of crop plants in the climate change we currently face.