Single-cell resolution of lineage trajectories in the Arabidopsis stomatal lineage and developing leaf

Dynamic cell identities underlie flexible developmental programs. The stomatal lineage in the Arabidopsis leaf epidermis features asynchronous and indeterminate divisions that can be modulated by environmental cues. The products of the lineage, stomatal guard cells and pavement cells, regulate plant-atmosphere exchanges, and the epidermis as a whole influences overall leaf growth. How flexibility is encoded in development of the stomatal lineage and how cell fates are coordinated in the leaf are open questions. Here, by leveraging single-cell transcriptomics and molecular genetics, we uncovered models of cell differentiation within Arabidopsis leaf tissue. Profiles across leaf tissues identified points of regulatory congruence. In the stomatal lineage, single-cell resolution resolved underlying cell heterogeneity within early stages and provided a fine-grained profile of guard cell differentiation. Through integration of genome-scale datasets and spatiotemporally precise functional manipulations, we also identified an extended role for the transcriptional regulator SPEECHLESS in reinforcing cell fate commitment.Peer reviewe

Ectopic callose deposition into woody biomass modulates the nano-architecture of macrofibrils

Plant biomass plays an increasingly important role in the circular bioeconomy, replacing non-renewable fossil resources. Genetic engineering of this lignocellulosic biomass could benefit biorefinery transformation chains by lowering economic and technological barriers to industrial processing. However, previous efforts have mostly targeted the major constituents of woody biomass: cellulose, hemicellulose and lignin. Here we report the engineering of wood structure through the introduction of callose, a polysaccharide novel to most secondary cell walls. Our multiscale analysis of genetically engineered poplar trees shows that callose deposition modulates cell wall porosity, water and lignin contents and increases the lignin-cellulose distance, ultimately resulting in substantially decreased biomass recalcitrance. We provide a model of the wood cell wall nano-architecture engineered to accommodate the hydrated callose inclusions. Ectopic polymer introduction into biomass manifests in new physico-chemical properties and offers new avenues when considering lignocellulose engineering.Bourdon et al. demonstrate the possibility to ectopically synthesize callose, a polymer restricted to primary cell walls, into Arabidopsis and aspen secondary cell walls to manipulate their ultrastructure and ultimately reduce their recalcitrance

Phloem-transported cytokinin regulates polar auxin transport and maintains vascular pattern in the root meristem

Cytokinin phytohormones regulate a variety of developmental processes in the root such as meristem size, vascular pattern, and root architecture [1, 2 and 3]. Long-distance transport of cytokinin is supported by the discovery of cytokinins in xylem and phloem sap [4] and by grafting experiments between wild-type and cytokinin biosynthesis mutants [5]. Acropetal transport of cytokinin (toward the shoot apex) has also been implicated in the control of shoot branching [6]. However, neither the mode of transport nor a developmental role has been shown for basipetal transport of cytokinin (toward the root apex). In this paper, we combine the use of a new technology that blocks symplastic connections in the phloem with a novel approach to visualize radiolabeled hormones in planta to examine the basipetal transport of cytokinin. We show that this occurs through symplastic connections in the phloem. The reduction of cytokinin levels in the phloem leads to a destabilization of the root vascular pattern in a manner similar to mutants affected in auxin transport or cytokinin signaling [7]. Together, our results demonstrate a role for long-distance basipetal transport of cytokinin in controlling polar auxin transport and maintaining the vascular pattern in the root meristem

Sphingolipid biosynthesis modulates plasmodesmal ultrastructure and phloem unloading.

During phloem unloading, multiple cell-to-cell transport events move organic substances to the root meristem. Although the primary unloading event from the sieve elements to the phloem pole pericycle has been characterized to some extent, little is known about post-sieve element unloading. Here, we report a novel gene, PHLOEM UNLOADING MODULATOR (PLM), in the absence of which plasmodesmata-mediated symplastic transport through the phloem pole pericycle-endodermis interface is specifically enhanced. Increased unloading is attributable to a defect in the formation of the endoplasmic reticulum-plasma membrane tethers during plasmodesmal morphogenesis, resulting in the majority of pores lacking a visible cytoplasmic sleeve. PLM encodes a putative enzyme required for the biosynthesis of sphingolipids with very-long-chain fatty acid. Taken together, our results indicate that post-sieve element unloading involves sphingolipid metabolism, which affects plasmodesmal ultrastructure. They also raise the question of how and why plasmodesmata with no cytoplasmic sleeve facilitate molecular trafficking.Finnish Centre of Excellence in Molecular Biology of Primary Producers (decision #271832) Gatsby Foundation (GAT3395/PR3) National Science Foundation Biotechnology and Biological Sciences Research Council grant (BB/N013158/1) University of Helsinki (award 799992091) ERC Advanced Investigator Grant SYMDEV (No. 323052

Research data supporting “Ectopic callose deposition into woody biomass modulates the nano-architecture of macrofibrils”

The repository is divided in distinct folders which contain the raw data necessary to produce each figure of the “Ectopic callose deposition into woody biomass modulates the nano-architecture of macrofibrils” manuscript. As such, each folder is named after the figure it is referring to, and often contains several subfolders distinguishing the different data sets necessary to produce each figure. Each subfolder name ends up with the initials of the main co-author(s) originating the data they contain. See the 'Repository_readme' file for a detailed description of this dataseto The UK High-Field Solid-State NMR Facility used in this research was funded by EPSRC and BBSRC (EP/T015063/1) as well as the University of Warwick including via part funding through Birmingham Science City Advanced Materials Projects 1 and 2 supported by Advantage West Midlands (AWM) and the European Regional Development Fund (ERDF). We thank the Cambridge Advanced Imaging Center (CAIC) for providing access to their TEM resources and for technical assistance in imaging. The lignin analysis was supported by the Soluserre funding (Région Pays de la Loire, France). The authors acknowledge the funding received from the New Zealand Ministry of Business, Innovation, and Employment (MBIE) Strategic Science Investment Fund (Contract No. C0X41703, High-Value Biorefineries Portfolio) for supporting this work. FV acknowledges support from the Swedish Research Council (grants 621-2014-5295 and 2020-04720) and from the Knut and Alice Wallenberg Foundation (through the Wallenberg Wood Science Centre). Work in the YBA lab is supported by the Leverhulme Trust (Grant RPG-2016-136) which funded S.A. and C.P. and the UKRI Future Leader Fellowship program (MR/T04263X/1). Work in the JJL lab is supported by a grant from the National Science Centre Poland awarded to JJL as part of the SONATINA 3 programme (project number 2019/32/C/NZ3/00392) and a grant from National Science Centre Poland awarded as part of SONATA 17 programme (project number 2021/43/D/NZ9/01978). MB was supported by the ERC Proof of Concept APPLICAL (2020-2022) and the HiLife Proof of Concept APPLICAL (2020-2021) grants. L.K. received funding from the SNSF (P2LAP3_178062) and a Marie Curie IEF (No. 795250). Work in the YH lab was supported by the Finnish CoE in Molecular Biology of Primary Producers (Academy of Finland CoE programme 2014–2019) decision n°. 271832, the Gatsby Foundation (GAT3395/PR3), the University of Helsinki (award 799992091) and the ERC Advanced Investigator Grant SYMDEV (No. 323052)