A cell wall-associated gene network shapes leaf boundary domains

Boundary domains delimit and organize organ growth throughout plant development almost relentlessly building plant architecture and morphogenesis. Boundary domains display reduced growth and orchestrate development of adjacent tissues in a non-cell autonomous manner. How these two functions are achieved remains elusive despite the identification of several boundary-specific genes. Here, we show using morphometrics at the organ and cellular levels that leaf boundary domain development requires SPINDLY (SPY), an O-fucosyltransferase, to act as cell growth repressor. Further we show that SPY acts redundantly with the CUP-SHAPED COTYLEDON transcription factors (CUC2 and CUC3), which are major determinants of boundaries development. Accordingly at the molecular level, CUC2 and SPY repress a common set of genes involved in cell wall loosening providing a molecular framework for the growth repression associated with boundary domains. Atomic force microscopy (AFM) confirmed that young leaf boundary domain cells have stiffer cell walls than marginal outgrowth. This differential cell wall stiffness was reduced in spy mutant. Taken together our data reveal a concealed CUC2 cell wall associated gene network linking tissue patterning with cell growth and mechanics.

Modeling Softening Kinetics at Cellular Scale and Phytochemicals Extractability in Cauliflower under Different Cooking Treatments

The effects induced by heat on Depurple and Cheddar (Brassica oleracea L. var. botrytis) during boiling, steaming, and sous-vide were investigated to elucidate the role of the basic cellular elements in softening and extractability of sterols and tocopherols. With this aim, an elastoplastic mechanical model was conceptualized at a cell scale-size and validated under creep experiments. The total amount of the phytochemicals was used to validate multivariate regression models in forecasting. Boiling was the most effective method to enhance the softening mechanisms causing tissue decompartmentalization through cell wall loosening with respect to those causing cell separation, having no impact on the phytochemical extractability. Sous-vide showed the lowest impact on cell wall integrity, but the highest in terms of cell separation. Steaming showed an intermediate behavior. Tissue of the Depurple cauliflower was the most resistant to the heat, irrespectively to the heating technology. Local heterogeneity in the cell wall and cell membrane, expected as a plant variety-dependent functional property, was proposed as a possible explanation because sterol extractability under lower heat-transfer efficiency, i.e., steaming and sous-vide, decreased in Depurple and increased in Cheddar as well as because the extractability of sterols and tocopherols was greater in Cheddar.

Auxin and pectin remodeling interplay during rootlet emergence in white lupin

Secondary root emergence is a crucial trait that shapes the plants underground system. Virtually every developmental step of root primordium morphogenesis is controlled by auxin. However, how the hormone controls cell separation in primordium-overlaying tissues through wall loosening is poorly understood. Here, we took advantage of white lupin and its spectacular cluster root development to assess the contribution of auxin to this process. We show that auxin positive role on rootlet emergence is associated with an upregulation of cell wall pectin modifying and degrading genes. Downregulation of a pectinolytic enzyme gene expressed in cells surrounding the primordium resulted in delayed emergence. Pectins were demethylesterified in the emergence zone and auxin treatment further enhanced this effect. Additionally, we report specific rhamnogalacturonan-I modifications during cortical cell separation. In conclusion, we propose a model in which auxin has a dual role during rootlet emergence: Firstly, through active pectin demethylesterification and secondly by regulating the expression of cell wall remodeling enzymes.

Transcriptome Analysis Reveals the Symbiotic Mechanism of Ustilago esculenta-Induced Gall Formation of Zizania latifolia

Zizania latifolia is a perennial aquatic vegetable, whose symbiosis with the fungus Ustilago esculenta (member of Basidiomycota, class Ustilaginaceae) results in the establishment of swollen gall formations. Here, we analyzed symbiotic relations of Z. latifolia and U. esculenta, using a triadimefon (TDF) treatment and transcriptome sequencing (RNA-seq). Specifically, accurately identify the whole growth cycle of Z. latifolia. Microstructure observations showed that the presence of U. esculenta could be clearly observed after gall formation but was absent after the TDF treatment. A total of 17,541 differentially expressed genes (DEGs) were identified, based on the transcriptome. According to gene ontology term and Kyoto Encyclopedia of Genes and Genomes pathway results, plant hormone signal transduction, and cell wall–loosening factors were all significantly enriched due to U. esculenta infecting Z. latifolia; relative expression levels of hormone-related genes were identified, of which downregulation of indole 3-acetic acid (IAA)-related DEGs was most pronounced in JB_D versus JB_B. The ultra–high performance liquid chromatography analysis revealed that IAA, zeatin+trans zeatin riboside, and gibberellin 3 were increased under U. esculenta infection. Based on our results, we proposed a hormone–cell wall loosening model to study the symbiotic mechanism of gall formation after U. esculenta infects Z. latifolia. Our study thus provides a new perspective for studying the physiological and molecular mechanisms of U. esculenta infection of Z. latifolia causing swollen gall formations as well as a theoretical basis for enhancing future yields of cultivated Z. latifolia. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CCO “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.

CcLBD25 functions as a key regulator of haustorium development in Cuscuta campestris

Parasitic plants reduce yield of crops worldwide. Cuscuta campestris is a stem parasite that attaches to its host, using haustoria to extract nutrients and water. We analyzed the transcriptome of six C. campestris tissues and identified a key gene, CcLBD25, as highly expressed in prehaustoria and haustoria. Our gene co-expression networks (GCN) from different tissue types and laser-capture microdissection (LCM) RNA-Seq data indicate that CcLBD25 could be essential for regulating cell wall loosening and organogenesis. We employed host-induced gene silencing (HIGS) by generating transgenic tomato hosts that express hairpin RNAs to target and down-regulate CcLBD25 in the parasite. Our results showed that C. campestris growing on CcLBD25 RNAi transgenic tomatoes transited to the flowering stage earlier and had less biomass compared with C. campestris growing on wild type host. This suggests that the parasites growing on the transgenic plants were stressed due to insufficient nutrient acquisition. Anatomy of C. campestris haustoria growing on CcLBD25 RNAi tomatoes showed reduced pectin digestion and lack of searching hyphae, which interfered with haustorium penetration and the formation of vascular connections. We developed an in vitro haustorium (IVH) system to assay the number of prehaustoria produced on strands from C. campestris. When C. campestris was grown on CcLBD25 RNAi tomatoes or wild type tomatoes, the former produce fewer prehaustoria than the latter, indicating that down-regulating CcLBD25 may affect haustorium initiation. The results of this study shed light on the role of CcLBD25 in haustorium development and might help to develop a parasite-resistant system in crops.One-sentence summaryCcLBD25 plays a pivotal role in haustorium initiation, regulating pectin digestion, and searching hyphae development during the haustorium penetration process.

Genome-Wide Identification of the Expansin Gene Family and Its Potential Association with Drought Stress in Moso Bamboo

Expansins, a group of cell wall-loosening proteins, are involved in cell-wall loosening and cell enlargement in a pH-dependent manner. According to previous study, they were involved in plant growth and abiotic stress responses. However, information on the biological function of the expansin gene in moso bamboo is still limited. In this study, we identified a total of 82 expansin genes in moso bamboo, clustered into four subfamilies (α-expansin (EXPA), β-expansin (EXPB), expansin-like A (EXLA) and expansin-like B (EXPB)). Subsequently, the molecular structure, chromosomal location and phylogenetic relationship of the expansin genes of Phyllostachys edulis (PeEXs) were further characterized. A total of 14 pairs of tandem duplication genes and 31 pairs of segmented duplication genes were also identified, which may promote the expansion of the expansin gene family. Promoter analysis found many cis-acting elements related to growth and development and stress response, especially abscisic acid response element (ABRE). Expression pattern revealed that most PeEXs have tissue expression specificity. Meanwhile, the expression of some selected PeEXs was significantly upregulated mostly under abscisic acid (ABA) and polyethylene glycol (PEG) treatment, which implied that these genes actively respond to expression under abiotic stress. This study provided new insights into the structure, evolution and function prediction of the expansin gene family in moso bamboo.

Apical-root apoplastic acidification affects cell-wall extensibility in wheat under salinity stress

Plant salt tolerance is closely associated with a high rate of root growth. Although root growth is governed by cell-wall and apoplastic pH, the relationship between these factors in the root elongation zone under salinity stress remains unclear. Here, we assess apoplastic pH, pH- and expansin-dependent cell-wall extensibility, and expansin expression in the root elongation zone of salt-sensitive (Yongliang-15) and -tolerant (JS-7) cultivars under salinity stress. A six-day 80 mM NaCl treatment significantly reduced apical-root apoplastic pH, from 6.2 to 5.3, in both cultivars. Using a pH-dependent cell-wall extensibility experiment, we found that, under 0 mM NaCl treatment, the optimal pH for cell-wall loosening was 6.0 in the salinity-tolerant cultivar and 4.6 in the salinity-sensitive cultivar. Under 80 mM treatment, a pH of 5.0 mitigated the cell-wall stiffness caused by salinity stress in the salinity-tolerant cultivar, but promoted cell-wall stiffening in the salinity-sensitive cultivar. These changes in pH-dependent cell-wall extensibility are consistent with differences in the root growth of two cultivars under salinity stress. Exogenous expansin application, and expansin expression experiments, we found that salinity stress altered expansin expression, differentially affecting cell-wall extensibility under pH 5.0 and 6.0. TaEXPA7 and TaEXPA8 induced cell-wall loosening at pH 5.0, whereas TaEXPA5 induced cell-wall loosening at pH 6.0. These results elucidate the relationship between expansin and cell-wall extensibility in the root elongation zone, with important implications for enhancing plant growth under salinity stress.

Mucilaginous Secretions in the Xylem and Leaf Apoplast of the Swamp Palm Mauritia flexuosa L.f. (Arecaceae)

Mauritia flexuosa palms inhabit wetland environments in the dry, seasonal Brazilian savanna (Cerrado) and produce mucilaginous secretions in the stem and petiole that have a medicinal value. The present study sought to characterize the chemical natures of those secretions and to describe the anatomical structures involved in their synthesis. Chemical analyzes of the secretions, anatomical, histochemical analyses, and electron microscopy studies were performed on the roots, stipes, petioles, and leaf blades. Stipe and petiole secretions are similar, and rich in cell wall polysaccharides and pectic compounds such as rhamnose, arabinose, xylose, mannose, galactose, and glucose, which are hydrophilic largely due to their hydroxyl and carboxylate groups. Mucilaginous secretions accumulate in the lumens of vessel elements and sclerenchyma fibers of the root, stipe, petiole, and foliar veins; their synthesis involves cell wall loosening and the activities of dictyosomes. The outer faces of the cell walls of the parenchyma tissue in the mesophyll expand to form pockets that rupture and release pectocellulose substances into the intercellular spaces. The presence of mucilage in the xylem, extending from the roots to the leaf veins and continuous with the leaf apoplast, and sub-stomatal chambers suggest a strategy for plant water economy.

Temporal expression patterns of fruit-specific α- EXPANSINS during cell expansion in bell pepper (Capsicum annuum L.)

Background Expansins (EXP) facilitate non-enzymatic cell wall loosening during several phases of plant growth and development including fruit growth, internode expansion, pollen tube growth, leaf and root development, and during abiotic stress responses. In this study, the spatial and temporal expression patterns of C. annuum α- EXPANSINS (CaEXPA) genes were characterized. Additionally, fruit-specific CaEXPA expression was correlated with the rate of cell expansion during bell pepper fruit development. Results Spatial expression patterns revealed that CaEXPA13 was up-regulated in vegetative tissues and flowers, with the most abundant expression in mature leaves. Expression of CaEXPA4 was associated with stems and roots. CaEXPA3 was expressed abundantly in flower at anthesis suggesting a role for CaEXPA3 in flower development. Temporal expression analysis revealed that 9 out of the 21 genes were highly expressed during fruit development. Of these, expression of six genes, CaEXPA5, CaEXPA7, CaEXPA12, CaEXPA14 CaEXPA17 and CaEXPA19 were abundant 7 to 21 days after anthesis (DAA), whereas CaEXP6 was strongly expressed between 14 and 28 DAA. Further, this study revealed that fruit growth and cell expansion occur throughout bell pepper development until ripening, with highest rates of fruit growth and cell expansion occurring between 7 and 14 DAA. The expression of CaEXPA14 and CaEXPA19 positively correlated with the rate of cell expansion, suggesting their role in post-mitotic cell expansion-mediated growth of the bell pepper fruit. In this study, a ripening specific EXP transcript, CaEXPA9 was identified, suggesting its role in cell wall disassembly during ripening.Conclusion This is the first genome-wide study of CaEXPA expression during fruit growth and development. Identification of a fruit-specific EXPAs suggest their importance in facilitating cell expansion during growth and cell wall loosening during ripening in bell pepper. These EXPA genes could be important targets for future manipulation of fruit size and ripening characteristics.