Biology subjects

Raissig, M. T.

Publications and source records attributed to Raissig, M. T..

8 recordsLinked to original sources

bioRxiv2026

A premitotic polarity program patterns the grass leaf epidermis

Transverse asymmetric cell divisions (ACDs) in grass leaf epidermal development produce large basal pavement cells and small apical specialised cells. These "patterning divisions" generate the long-short epidermal cell pattern that is distinctive of grasses. Here, we show that patterning divisions require premitotic basal polarisation of Bd-POLAR-LIKE1 (BdPL1) in the model grass Brachypodium distachyon. Loss of BdPL1 disrupted division-plane orientation and postmitotic cell-size asymmetry in all cell files, which resulted in epidermal patterning defects. Ectopic expression analyses demonstrated that BdPL1 polarisation was independent of cellular context and sufficient to promote supernumerary transverse divisions. Furthermore, the developmental regulators BdBREVIS RADIX-solo and BdYODA1 formed a post-division polarity domain enforcing cell fate asymmetry independently of BdPL1. We propose that the premitotic BdPL1 module enforces physical cell-division asymmetry contributing to medio-lateral patterning of cell types, whereas the postmitotic BdBRX-solo/ BdYDA1 module enforces within-file cell fate asymmetry. Together, they robustly pattern the grass leaf epidermis.

plant biology↗

bioRxiv2025

The developing leaf of the wild grass Brachypodium distachyon at single-cell resolution

Leaves are the plants main photosynthetic organs and drive Earths primary production. Grasses form longitudinal leaves with parallel venation and graminoid stomata. Yet, how distinct leaf tissues coordinatively develop to build functional grass leaf anatomy is not well understood. Here, we decoded the developing grass leaf from vegetative meristems to mature tissues using single-cell RNA-sequencing in the wild grass Brachypodium distachyon. In-depth analysis of epidermal clusters and multiplexed whole-mount RNA-fluorescence in situ hybridization resolved most epidermal lineages and confirmed them in planta. Gene regulatory network analysis distinguished the targetome of the two co-expressed, yet functionally divergent stomatal transcription factors BdMUTE and BdFAMA. Finally, we used our dataset to identify and functionally describe BdGRAS32s role in cell division inhibition and a stomata-specific function for a cell wall modifying enzyme. Together, our single-cell grass leaf atlas enables the dissection of developmental processes that shape the leaf sustaining global food production.

plant biology↗

bioRxiv2024

MUTE drives asymmetric divisions to form stomatal subsidiary cells in Crassulaceae succulents

Amongst the evolutionary innovations of many succulents is a photosynthetic lifestyle, where stomatal gas exchange is decoupled from light-dependent carbon fixation. Stomatal complexes in the emerging succulent model Kalanchoe laxiflora consist of two guard cells surrounded by three anisocytic subsidiary cells (SCs). Here, we show that these SCs shuttle ions and thus likely support stomatal movements. Furthermore, gene editing, reporter lines and protein overexpression implicate the stomatal transcription factor MUTE in facilitating additional rounds of asymmetric divisions that form SCs in succulents. This is opposite to the role of MUTE in Arabidopsis thaliana, where it stops rather than induces asymmetric divisions, but reminiscent of MUTEs SC-related function in grasses. Together, our work deciphers an intricate genetic mechanism that generates innovative stomatal morphology in Crassulaceae succulents.

plant biology↗

bioRxiv2024

Dual role of BdMUTE during stomatal development in the model grass Brachypodium distachyon

Grasses form morphologically derived, four-celled stomata, where two dumbbell-shaped guard cells (GCs) are flanked by two lateral subsidiary cells (SCs). This innovative form enables rapid opening and closing kinetics and efficient plant-atmosphere gas exchange. The mobile bHLH transcription factor MUTE is required for SC formation in grasses. Yet, if and how MUTE also regulates GC development and if MUTE mobility is required for SC recruitment is unclear. Here, we transgenically impaired BdMUTE mobility from GC to SC precursors in the emerging model grass Brachypodium distachyon. Our data indicates that reduced BdMUTE mobility severely affected the spatiotemporal coordination of GC and SC development. Furthermore, while BdMUTE has a cell-autonomous role in GC division orientation, complete dumbbell morphogenesis of GCs required SC recruitment. Finally, leaf-level gas exchange measurements showed that dosage-dependent complementation of the four-celled grass morphology was mirrored in a gradual physiological complementation of stomatal kinetics. Together, our work revealed a dual role of grass MUTE in regulating GC division orientation and SC recruitment, which in turn was required for GC morphogenesis and the rapid kinetics of grass stomata.

plant biology↗

bioRxiv2022

A hair cell-specific peroxidase coordinates stomatal and prickle hair cell size to optimize epidermal cell functionality in grasses

The leaf epidermis is the outermost cell layer forming the interface between plants and the atmosphere that must both provide a robust barrier against (a)biotic stressors and facilitate carbon dioxide uptake and leaf transpiration 1. To achieve these opposing requirements, the plant epidermis developed a wide range of specialized cell types such as stomata and hair cells. While factors forming these individual cell types are known 2-5, it is poorly understood how their number and size is coordinated. Here, we identified a role for BdPRX76/BdPOX, a class III peroxidase, in regulating hair cell and stomatal size in the model grass Brachypodium distachyon. In bdpox mutants prickle hair cells were smaller and stomata were longer. Because stomatal density remained unchanged, the negative correlation between stomatal size and density was disrupted in bdpox and resulted in higher stomatal conductance and lower intrinsic water-use efficiency. BdPOX was exclusively expressed in hair cells suggesting that BdPOX cell-autonomously promotes hair cell size and indirectly restricts stomatal length. Cell wall autofluorescence and lignin stainings indicated a role for BdPOX in lignification or crosslinking of related phenolic compounds at the hair cell base. Ectopic expression of BdPOX in the stomatal lineage increased phenolic autofluorescence in guard cell walls and restricted stomatal elongation in bdpox. Together, we highlight a developmental interplay between hair cells and stomata that optimizes epidermal functionality. We propose that cell-type-specific changes disrupt this interplay and lead to compensatory developmental defects in other epidermal cell types.

plant biology↗

bioRxiv2022

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. Using the genetic model grass Brachypodium distachyon, we identified BdPOLAR, which forms a novel, distal polarity domain in SMCs that is reciprocal to the proximal PAN1 domain. Both polarity domains are required for the formative SC division yet exhibit distinct roles in regulating 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.

plant biology↗

bioRxiv2021

Quantitative effects of environmental variation on stomatal anatomy and gas exchange in a grass model

Stomata are cellular pores on the leaf epidermis that allow plants to regulate carbon assimilation and water loss. Stomata integrate environmental signals to regulate pore apertures and optimize gas exchange to fluctuating conditions. Here, we quantified intraspecific plasticity of stomatal gas exchange and anatomy in response to seasonal variation in Brachypodium distachyon. Over the course of two years we (i) used infrared gas analysis to assess light response kinetics of 120 Bd21-3 wild-type individuals in an environmentally fluctuating greenhouse and (ii) microscopically determined the seasonal variability of stomatal anatomy in a subset of these plants. We observed systemic environmental effects on gas exchange measurements and remarkable intraspecific plasticity of stomatal anatomical traits. To reliably link anatomical variation to gas exchange, we adjusted anatomical gsmax calculations for grass stomatal morphology. We propose that systemic effects and variability in stomatal anatomy should be accounted for in long-term gas exchange studies.

plant biology↗

bioRxiv2017

Consistent Reanalysis of Genome-wide Imprinting Studies in Plants Using Generalized Linear Models Increases Concordance across Datasets

Genomic imprinting leads to different expression levels of maternally and paternally derived alleles. Over the last years, major progress has been made in identifying novel imprinted candidate genes in plants, owing to affordable next-generation sequencing technologies. However, reports on sequencing the transcriptome of hybrid F1 seed tissues strongly disagree about how many and which genes are imprinted. This raises questions about the relative impact of biological, environmental, technical, and analytic differences or biases. Here, we adopt a statistical approach, frequently used in RNA-seq data analysis, which properly models count overdispersion and considers replicate information of reciprocal crosses. We show that our statistical pipeline outperforms other methods in identifying imprinted genes in simulated and real data. Accordingly, reanalysis of genome-wide imprinting studies in Arabidopsis and maize shows that, at least for the Arabidopsis dataset, an increased agreement across datasets can be observed. For maize, however, consistent reanalysis did not yield in a larger overlap between the datasets. This suggests that the discrepancy across publications might be partially due to different analysis pipelines but that technical, biological, and environmental factors underlie much of the discrepancy between datasets. Finally, we show that the set of genes that can be characterized regarding allelic bias by all studies with minimal confidence is small (~8,000/27,416 genes for Arabidopsis and ~12,000/39,469 for maize). In conclusion, we propose to use biologically replicated reciprocal crosses, high sequence coverage, and a generalized linear model approach to identify differentially expressed alleles in developing seeds.

plant biology↗