Exosomes in the phloem and xylem of woody plants

Exosomes in the secondary phloem and secondary xylem of angiosperms and gymnosperms have physiological roles in the storage and transport of endoglucanases. Knowledge of plant extracellular vesicles (EVs) is limited by their presence in the apoplastic fluid of seeds and leaves. The contents of plant EVs and their biological functions are unclear. The aim of the present study was to expand our knowledge of EVs in woody plants. Sample splits were prepared from branch and stem samples from angiosperms and gymnosperms after cryomechanical destruction with liquid nitrogen. The study methods included scanning electron (SEM), atomic force microscopy (AFM), endoglucanase activity measurement. EVs visualized on the internal layers of the cell walls proved to be exosomes according to their diameter (65-145 nm). SEM revealed cup-shaped structures characteristic of exosomes in a dry state. Plant exosomes in the form of globules in the native state were visualized for the first time by AFM. Exosomes were present both in the active and dormant cambium. Erosion zones were observed at the sites of exosome localization. The activity of endo-1,4-β-glucanase was detected in Picea xylem, while the RNA level was very low, suggesting that endo-1,4-β-glucanases were preserved in the exosomes. There are grounds to assert that endo-1,4-β-glucanases delivered by exosomes participated in pit cavity formation in the S₁ layer of xylary fibres. A possible mechanism of endo-1,4-β-glucanase action in the biosynthesis of the secondary wall is proposed. These results demonstrate that the physiological role of the exosomes in the phloem and xylem is the storage and transport of endo-1,4-β-glucanases participating in cell wall remodeling in woody plants. Present study expands our knowledge about plant exosomes.

An auxin-induced β-type endo-1,4-β-glucanase in poplar is involved in cell expansion and lateral root formation

PtrGH9A7, a poplar β-type endo-1,4-β-glucanase gene induced by auxin, promotes both plant growth and lateral root development by enhancing cell expansion. Endo-1,4-β-glucanase (EGase) family genes function in multiple aspects of plant growth and development. Our previous study found that PtrCel9A6, a poplar EGase gene of the β subfamily, is specifically expressed in xylem tissue and is involved in the cellulose biosynthesis required for secondary cell wall formation (Yu et al. in Mol Plant 6:1904-1917, 2013). To further explore the functions and regulatory mechanism of β-subfamily EGases, we cloned and characterized another poplar β-type EGase gene PtrGH9A7, a close homolog of PtrCel9A6. In contrast to PtrCel9A6, PtrGH9A7 is predominantly expressed in parenchyma tissues of the above-ground part; in roots, PtrGH9A7 expression is specifically restricted to lateral root primordia at all stages from initiation to emergence and is strongly induced by auxin application. Heterologous overexpression of PtrGH9A7 promotes plant growth by enhancing cell expansion, suggesting a conserved role for β-type EGases in 1,4-β-glucan chains remodeling, which is required for cell wall loosening. Moreover, the overexpression of PtrGH9A7 significantly increases lateral root number, which might result from improved lateral root primordium development due to enhanced cell expansion. Taken together, these results demonstrate that this β-type EGase induced by auxin signaling has a novel role in promoting lateral root formation as well as in enhancing plant growth.

Enhanced Production of a Recombinant Multidomain Thermostable GH9 Processive Endo-1,4-β-Glucanase (CenC) from Ruminiclostridium thermocellum in a Mesophilic Host Through Various Cultivation and Induction Strategies

Commonly, unintentional induction and inadvertently preparing medium for engineered Escherichia coli BL21 CodonPlus (DE3)-RIPL, give poor or variable yields of heterologous proteins. Therefore, to enhance the activity and production of an industrially relevant recombinant processive endo-1,4-β-glucanase (CenC) propagated in Escherichia coli BL21 CodonPlus(DE3)-RIPL through various cultivation and induction strategies. Investigation of various growth media and induction parameters revealed that high-cell-density and optimal CenC expression were obtained in ZYBM9 medium induced either with 0.5 mM IPTG/150 mM lactose, after 6 h induction at 37 °C; and before induction, bacterial cells were given heat shock (42 °C) for 1 h when culture density (OD_600nm) reached at 0.6. Intracellular enzyme activity was enhanced by 6.67 and 3.20-fold in ZYBM9 and 3×ZYBM9 medium, respectively, under optimal conditions. Using YNG auto-induction medium, activity was 2.5-fold increased after 10 h incubation at 37 °C. Approximately similar results were obtained by transferring the optimized process at the bioreactor level. Results showed that the effective process strategy is essential to enhance recombinant bacterial cell mass and enzyme production from small to large-scale. To the best of our knowledge, this is the first ever report on enhanced production of thermostable processive endo-1,4-β-glucanase cloned from Ruminiclostridium thermocellum, which is a suitable candidate for industrial applications. Graphical Abstract Flow Chart Summary of Enhanced Production of a Recombinant Multidomain Thermostable GH9 Processive Endo-1,4-β-glucanase from Ruminiclostridium thermocellum.

Purification, Characterization, and Gene Cloning of a Cold-Adapted Endo-1,4-β-glucanase from Bellamya chinensis laeta

An endo-1,4-β-glucanase from Bellamya chinensis laeta was purified to electrophoretically homogeneous state. The molecular weight of the purified enzyme was estimated 70,000 by SDS-PAGE. The enzyme was most active at pH 5.5 and 50 °C, and stable at around pH 10 and 50 °C. The enzyme exhibited the significant activity at 20 °C (30 % of the activity at optimal 50 °C). The enzyme was hydrolyzed cellohexaose into cellobiose, cellotriose, and cellotetraose as main products. Three cDNAs (BC-EG70a, BC-EG70b, and BC-EG70c) encoding the endo-1,4-β-glucanase were cloned by PCR-based method. Three endo-1,4-β-glucanases consisted of 1758 bp encoding 586 amino acids. The three genes were almost the same nucleotide sequences. The deduced proteins were consisted of a signal sequence, cellulose binding domain, linker, and catalytic domain. The amino acid sequence of BC-EG70a shares sequence identity degree with the endo-1,4-β-glucanases of Haliotis discus hannai (61 %), Ampullaria crossean (52 %), and Mizuhopecten yessoensis (51 %) which all belong to glycoside hydrolase family 9.