Plant Development: Suppression the Key to Asymmetric Cell Fate

A new study shows that SPEECHLESS determines cell fate in the stomatal lineage but is inherited equally by daughter cells following an asymmetric cell division. The polarity determinant BASL acts as a MAPK scaffold, targeting SPEECHLESS for degradation in the larger daughter cell

Plant Development: Suppression the Key to Asymmetric Cell Fate

A new study shows that SPEECHLESS determines cell fate in the stomatal lineage but is inherited equally by daughter cells following an asymmetric cell division. The polarity determinant BASL acts as a MAPK scaffold, targeting SPEECHLESS for degradation in the larger daughter cell

Origins and evolution of stomatal development

The fossil record suggests stomata-like pores were present on the surfaces of land plants over 400 million years ago. Whether stomata arose once or whether they arose independently across newly evolving land plant lineages has long been a matter of debate. In Arabidopsis, a genetic toolbox has been identified that tightly controls stomatal development and patterning. This includes the basic helix-loop-helix (bHLH) transcription factors SPEECHLESS (SPCH), MUTE, FAMA, and ICE/SCREAMs (SCRMs), which promote stomatal formation. These factors are regulated via a signaling cascade, which includes mobile EPIDERMAL PATTERNING FACTOR (EPF) peptides to enforce stomatal spacing. Mosses and hornworts, the most ancient extant lineages to possess stomata, possess orthologs of these Arabidopsis (Arabidopsis thaliana) stomatal toolbox genes, and manipulation in the model bryophyte Physcomitrella patens has shown that the bHLH and EPF components are also required for moss stomatal development and patterning. This supports an ancient and tightly conserved genetic origin of stomata. Here, we review recent discoveries and, by interrogating newly available plant genomes, we advance the story of stomatal development and patterning across land plant evolution. Furthermore, we identify potential orthologs of the key toolbox genes in a hornwort, further supporting a single ancient genetic origin of stomata in the ancestor to all stomatous land plants

Does molecular and structural evolution shape the speedy grass stomata?

It has been increasingly important for breeding programs to be aimed at crops that are capable of coping with a changing climate, especially with regards to higher frequency and intensity of drought events. Grass stomatal complex has been proposed as an important factor that may enable grasses to adapt to water stress and variable climate conditions. There are many studies focusing on the stomatal morphology and development in the eudicot model plant Arabidopsis and monocot model plant Brachypodium. However, the comprehensive understanding of the distinction of stomatal structure and development between monocots and eudicots, especially between grasses and eudicots, are still less known at evolutionary and comparative genetic levels. Therefore, we employed the newly released version of the One Thousand Plant Transcriptome (OneKP) database and existing databases of green plant genome assemblies to explore the evolution of gene families that contributed to the formation of the unique structure and development of grass stomata. This review emphasizes the differential stomatal morphology, developmental mechanisms, and guard cell signaling in monocots and eudicots. We provide a summary of useful molecular evidences for the high water use efficiency of grass stomata that may offer new horizons for future success in breeding climate resilient crops

Origins and evolution of stomatal development

The fossil record suggests stomata-like pores were present on the surfaces of land plants over 400 million years ago. Whether stomata arose once or whether they arose independently across newly evolving land plant lineages has long been a matter of debate. In Arabidopsis, a genetic toolbox has been identified that tightly controls stomatal development and patterning. This includes the basic helix-loop-helix (bHLH) transcription factors SPEECHLESS (SPCH), MUTE, FAMA, and ICE/SCREAMs (SCRMs), which promote stomatal formation. These factors are regulated via a signaling cascade, which includes mobile EPIDERMAL PATTERNING FACTOR (EPF) peptides to enforce stomatal spacing. Mosses and hornworts, the most ancient extant lineages to possess stomata, possess orthologs of these Arabidopsis (Arabidopsis thaliana) stomatal toolbox genes, and manipulation in the model bryophyte Physcomitrella patens has shown that the bHLH and EPF components are also required for moss stomatal development and patterning. This supports an ancient and tightly conserved genetic origin of stomata. Here, we review recent discoveries and, by interrogating newly available plant genomes, we advance the story of stomatal development and patterning across land plant evolution. Furthermore, we identify potential orthologs of the key toolbox genes in a hornwort, further supporting a single ancient genetic origin of stomata in the ancestor to all stomatous land plants

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. © Copyright © 2021 Han, Kwak and Qi.1

Reducing stomatal density in barley improves drought tolerance without impacting on yield.

The epidermal patterning factor (EPF) family of secreted signalling peptides regulate the frequency of stomatal development in model dicot and basal land plant species. Here we identify and manipulate the expression of a barley ortholog and demonstrate that when overexpressed HvEPF1 limits entry to, and progression through, the stomatal development pathway. Despite substantial reductions in leaf gas exchange, barley plants with approximately half of the normal number of stomata show no reductions in grain yield. In addition, HvEPF1OE barley lines exhibit significantly enhanced water use efficiency, drought tolerance and soil water conservation properties. Our results demonstrate the potential of manipulating stomatal frequency for the protection and optimisation of cereal crop yields under future drier environments

Elucidating the role of receptor like kinases ERf in plant development

Intercellular communication is indispensable for development of complex multicellular organisms. Cell to cell communication in plants is heavily reliant on receptor-like-kinases (RLKs) located on the surface of cells. ERECTA (ER) and its two paralogs ERECTA-like 1 (ERL1) and ERL2 are leucine-rich repeats RLKs that regulate multiple developmental processes. Ligands of the ERf receptors are small secreted peptides known as Epidermal Patterning Factor-Like (EPFL). In Arabidopsis, the EPFL family is made of 11 genes, several of which remain to be characterized. Results presented in this work include:1) The use of structure function analysis found that juxtamembrane domain and kinase activity is essential for ERECTA signaling activity while the carboxy-terminal tail is not. Analysis of the activation loop in the kinase domain revealed the importance of phosphorylation sites that modulate the signaling of ERECTA. Lastly, not all developmental processes regulated by the ERECTA family require kinase activity suggesting that there are different mechanisms for stomata development and regulation of organ growth.2) Ectopic expression of ERECTA in specified regions of the shoot apical meristem (SAM) releveled that central zone expression was sufficient to rescue the meristem size and leaf initiation defects of er erl1 erl2 mutant. Transcriptional reporter lines identified the putative ER family ligands that were expressed near the SAM. A genetics approach reveled EPFL1, EPFL2, EPFL4 and EPFL6 to redundantly regulate meristem size and rate of leaf initiation. Lastly, ectopic expression of EPFL1 in the peripheral zone of the SAM rescued SAM phenotypes of the epfl1 epfl2 epfl4 eplf6 mutant. These results suggest that the ERECTA family signaling pathway mediates communication between the peripheral zone and central zone of the SAM.This work expands our knowledge of ERECTA family signaling and its implementation in the role of SAM regulation