A bHLH Transcription Factor Regulates Bisbibenzyl Biosynthesis in the Liverwort Plagiochasma appendiculatum

Liverworts, a section of the bryophyte plants which pioneered the colonization of terrestrial habitats, produce cyclic bisbibenzyls as secondary metabolites. These compounds are generated via the phenylpropanoid pathway, similar to flavonoid biosynthesis, for which basic helix-loop-helix (bHLH) transcription factors have been identified as one of the important regulators in higher plants. Here, a bHLH gene homolog (PabHLH) was isolated from the liverwort species Plagiochasma appendiculatum and its contribution to bisbibenzyl biosynthesis was explored. Variation in the abundance of PabHLH transcript mirrored that of tissue bisbibenzyl content in three different liverwort tissues. A phylogenetic analysis based on the bHLH domain sequence suggested that the gene encodes a member of bHLH subgroup IIIf, which clusters proteins involved in flavonoid synthesis. The gene's transient expression in onion epidermal cells implied that its product localized to the nucleus, and a transactivation assays in yeast showed that it was able to activate transcription. In both callus and thallus, the overexpression of PabHLH boosted bisbibenzyl accumulation, while also up-regulating PaPAL, Pa4CL1, PaSTCS1 and two genes encoding P450 cytochromes, and its RNA interference (RNAi)-induced suppression down-regulated the same set of genes and reduced the accumulation of bisbibenzyls. The abundance of PaCHS and PaFNSI transcript was related to flavonoid accumulation in transgenic thallus. PabHLH represents a candidate for the metabolic engineering of bisbibenzyl content.

Evolution of apolar sporocytes in marchantialean liverworts: implications from molecular phylogeny

In meiosis of basal land plants, meiotic division planes are typically predicted by quadri-lobing of the cytoplasm and/or quadri-partitioning of plastids prior to nuclear divisions. However, sporocytes of several marchantialean liverworts display no indication of premeiotic establishment of quadripolarity, as is observed in flowering plants. In these cases, the shape of sporocytes remains spherical or elliptical and numerous plastids are distributed randomly in the cytoplasm during meiosis. Through a survey of sporocyte morphology in marchantialean liverworts, we newly report the occurrence of apolar sporocytes in Sauteria japonica and Athalamia nana (Cleveaceae; Marchantiales). Molecular phylogenetic analyses revealed that the quadri-lobing of cytoplasm and quadri-partitioning of plastids were lost independently several times during the evolution of marchantialean liverworts. In addition, our phylogenetic analyses indicate that the simplified sporophytes of several marchantialean liverworts are not a primitive condition but rather represent the result of reductive evolution. The loss of the quadripolarity of sporocytes appears to correlate with the evolutionary trend of the sporophyte towards reductions. Through the evolution of the simplified sporophytes, suppression of mitotic divisions of sporogenous cells might had caused not only the modification of sporophyte ontogeny but also the drastic cytological change of sporocyte.

A new family of leafy liverworts from the middle Eocene of Vancouver Island, British Columbia, Canada

PREMISE OF THE STUDY

Morphology is a reflection of evolution, and as the majority of biodiversity that has lived on Earth is now extinct, the study of the fossil record provides a more complete picture of evolution. This study investigates anatomically preserved bryophyte fossils from the Eocene Oyster Bay Formation of Vancouver Island. While the bryophyte fossil record is limited in general, anatomically preserved bryophytes are even more infrequent; thus, the Oyster Bay bryophytes are a particularly significant addition to the bryophyte fossil record.

METHODS

Fossils occur in two marine carbonate nodules collected from the Appian Way locality on the eastern shore of Vancouver Island, British Columbia, and were prepared using the cellulose acetate peel technique.

KEY RESULTS

The fossils exhibit a novel combination of characters unknown among extinct and extant liverworts: (1) three-ranked helical phyllotaxis with underleaves larger than the lateral leaves; (2) fascicled rhizoids associated with the leaves of all three ranks; (3) Anomoclada-type endogenous branching.

CONCLUSIONS

A new liverwort family, Appianacae fam. nov., is established based upon the novel combination of characters. Appiana gen. nov. broadens the known diversity of bryophytes and adds a hepatic component to one of the richest and best characterized Eocene floras.

Effect of cold and menthol on membrane potential in plants

In animals, cooling substances such as menthol are perceived as cold sensation because they bind to the same receptor TRPM8 (transient receptor potential melastatin) that activates upon temperature drops. We investigated the effect of menthol on the plant membrane potential to search for analogies between animal and plant perception systems. The study was conducted on the liverwort Conocephalum conicum- a non-vascular plant generating action potentials (APs) in response to different stimuli including cold. (+)Menthol, (-)menthol and (+/-)menthol induced one or more APs, depending on the concentration. In contrast to animal reactions to menthol, threshold concentrations of these isomers were the same (1 mM). The presence of menthol in medium shortened cold-induced APs, whereas low temperature prolonged the repolarization phase of AP evoked by menthol. Cells of C. conicum with anion and potassium channels blocked by anthracene-9-carboxylic acid (A9C) and tetraethylammonium chloride (TEACl) generate short spike-like voltage transients (VTs) in response to cold and light stimulation. Membrane potential changes evoked by menthol in A9C- and TEACl-treated plants differed significantly from VTs - lasted much longer and frequently occurred in series. 5 mM LaCl(3) , 1 mM EGTA (ethylene glycol-bis(2-aminoethyl ether)-N,N,N',N'-tetraacetic acid) (0 Ca(2+) ) but not 0.2 mM verapamil blocked the putative calcium component of AP induced by menthol. Similar inhibitory effect was observed after the application of proton pump inhibitors: 0.05 mM N,N-dicyclohexylcarbodiimide (DCCD), 0.05 mM diethylstilbestrol (DES) or 0.01 mM carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP). Our results indicate that cold and menthol act independently, activating different membrane transporters in C. conicum cells.

Diversity in meiotic spindle origin and determination of cytokinetic planes in sporogenesis of complex thalloid liverworts (Marchantiopsida)

As the earliest divergent land plants, bryophytes (mosses, hornworts, and liverworts) provide insight into the evolution of the unique plant process of sporogenesis by which meiosis results in heavy walled spores. New immunohistochemical data on microtubules and gamma-tubulin in four genera of complex thalloid liverworts combined with previously published data on another four genera demonstrate grades in the evolution of spindle organization in meiosis. We have discovered that all recognized forms of microtubule organizing centers (MTOCs) in plant cells (plastid MTOCs, spheroid cytoplasmic MTOCs, polar organizers, and nuclear envelope MTOCs) occur in organization of the meiotic spindle of complex thalloid liverworts. In addition, all aspects of pre-meiotic preparation for quadripartitioning of the sporocyte into a tetrad of spores occur, with the exception of pre-meiotic wall precursors found in certain simple thalloids. The preparation includes morphogenetic plastid migration, cortical bands of microtubules that mark future cytokinetic planes in pre-meiosis, quadrilobing of the cytoplasm during meiotic prophase, and quadripolar microtubule systems that are transformed into functionally bipolar metaphase I spindles. Quadripolar spindle origin is typical of bryophyte sporogenesis even though the MTOCs involved may differ. However, in certain crown taxa of complex thalloids the spindle develops with no traces of quadripolarity and placement of intersporal walls is determined after meiosis, as is typical of higher plants.

Desiccation tolerance in red and green gametophytes of Jamesoniella colorata in relation to photoprotection

This study tests the hypothesis that red-leaved gametophytes of the liverwort Jamesoniella colorata (Lehm.) Schiffn., which are found in relatively dry habitats, are more desiccation tolerant than their green counterparts, which are found in moister environments, through superior photoprotective systems. The potential role of red foliar pigments in relation to water deficits is investigated by measuring cell water-relations, oxidative damage and photosynthetic responses. The presence of red pigments, or other cellular constituents, did not affect cell water-relations during dehydration and thus appear not to be involved in cell osmotic regulation. During drying, both colour morphs showed a similar non-photochemical quenching activity and did not experience significant oxidative damage, as measured by the amounts of ascorbate, malondialdehyde and photosynthetic pigments. However, the levels of oxidative damage increased directly upon rewetting the gametophytes, especially in low light conditions (25 micromol m(-2) s(-1)). The efficiency of photosystem II only recovered partially after severe water deficits in both phenotypes. However, the red gametophytes recovered faster and more completely from mild water deficits than did the greens. Moreover, they experienced significantly less photobleaching after rehydration in low light. It is suggested that red pigments and/or carotenoids in these gametophytes improve desiccation tolerance by alleviating photooxidative damage.

Airborne sperm of Conocephalum conicum (Conocephalaceae)

We have obtained the first momentary photographs of sperms just as they are discharged from the antheridium of a liverwort, Conocephalum conicum, and have succeeded in monitoring the airborne sperms of bryophytes under field conditions. Airborne sperm of liverworts seems to be an effective strategy for raising the efficiency of fertilization between male and female plants separated in a drought environment.

Lunularia cruciata, a potential in vitro host for Glomus proliferum and G. intraradices

A study was conducted to define culture conditions for in vitro growth arbuscular mycorrhizal fungi (AMF) with liverworts as hosts. Lunularia cruciata (L.) Dumortier ex. Lindberg developed in vitro monoxenic mycothalli with both Glomus proliferum Dalpé & Declerck (MUCL 41827) and Glomus intraradices Schenck & Smith (MUCL 43204). AMF inoculated plants were co-cultured in plastic Petri dishes with semi-solidified medium supplemented with sucrose and grown under filtered light. Mycothalli of L. cruciata produced external hyphae and spores in quantities equivalent to those obtained with Ri T-DNA transformed root systems.

Accumulation, localisation, and toxic effects of cadmium in the liverwort Lunularia cruciata

Accumulation, tissue and intracellular localisation, and toxic effects of cadmium were investigated in the liverwort Lunularia cruciata. The results of analyses carried out by atomic absorption spectrometry on single plants showed that the cadmium accumulation was dose- and time-dependent. Cadmium localisation was assessed by X-ray scanning electron microscopy microanalysis in gemmalings and in the different tissues of the thallus and by X-ray transmission electron microscopy microanalysis at the cellular level. The metal preferentially accumulated in the hyaline parenchyma and at the base of the gemma cups. Inside the cell, cadmium accumulated in the vacuoles and the cell wall. Metal accumulation was accompanied by a concomitant increase in sulphur content within the vacuoles of stressed cells. Gel-permeation chromatography showed that most of the cadmium was associated with a low-molecular-mass fraction eluting at a ratio of elution volume to void volume corresponding to that of phytochelatins. The excess of sulphur deposited in the vacuoles may well have been caused by the stress-induced synthesis of phytochelatins. At the ultrastructural level, sublethal concentrations of cadmium caused alterations of the fine structure of the cells, inducing marked alterations of the chloroplast structure. Cadmium also induced a dose-dependent inhibition of apical thallus growth and gemma germination.

Fragments of the earliest land plants

The earliest fossil evidence for land plants comes from microscopic dispersed spores. These microfossils are abundant and widely distributed in sediments, and the earliest generally accepted reports are from rocks of mid-Ordovician age (Llanvirn, 475 million years ago). Although distribution, morphology and ultrastructure of the spores indicate that they are derived from terrestrial plants, possibly early relatives of the bryophytes, this interpretation remains controversial as there is little in the way of direct evidence for the parent plants. An additional complicating factor is that there is a significant hiatus between the appearance of the first dispersed spores and fossils of relatively complete land plants (megafossils): spores predate the earliest megafossils (Late Silurian, 425 million year ago) by some 50 million years. Here we report the description of spore-containing plant fragments from Ordovician rocks of Oman. These fossils provide direct evidence for the nature of the spore-producing plants. They confirm that the earliest spores developed in large numbers within sporangia, providing strong evidence that they are the fossilized remains of bona fide land plants. Furthermore, analysis of spore wall ultrastructure supports liverwort affinities.

The placenta in Monoclea forsteri Hook. and Treubia lacunosa (Col.) Prosk: insights into placental evolution in liverworts

Placental morphology is remarkably diverse between major bryophyte groups, especially with regard to the presence and distribution of transfer cells in the sporophyte and gametophyte. In contrast, with the exception of metzgerialean liverworts, placental morphology is highly conserved within major bryophyte groups. Here we examine the ultrastructure of the placenta in Monoclea forsteri and Treubia lacunosa, basal members of the marchantialean and metzgerialean liverwort lineages, respectively. In both species several layers of transfer cells are found on both sides of the placenta, with sporophytic transfer cells exhibiting prominent wall labyrinths. Consistent with previous reports of a similar placenta in other putatively basal and isolated liverwort genera such as Fossombronia, Haplomitrium, Blasia and Sphaerocarpos, this finding suggests that this type of placenta represents the plesiomorphic (primitive) condition in liverworts. Distinctive ultrastructural features of placental cells in Monoclea include branched plasmodesmata in the sporophyte and prominent arrays of smooth endoplasmic reticulum, seemingly active in secretion in the gametophyte. These arrays contain a core of narrow tubules interconnected by electron-opaque rods, structures with no precedent in plants. Analysis of the distribution of different types of placenta in major bryophyte groups provides valuable insights into their inter-relationships and possible phylogeny.

Organellar inheritance in liverworts: an example of Pellia borealis

Liverwort Pellia borealis is an allopolyploid species that originated after the hybridization and chromosome doubling of two cryptic species; Pellia epiphylla species N and Pellia epiphylla species S. A sequence comparison of chloroplast tRNAUCCGly, tRNAUUULys gene introns, the mitochondrial tRNAGCUSer gene intron, and the first intron of the coxIII gene in the case of three liverwort species studied revealed that the chloroplast and mitochondrial sequences are identical in P. borealis and P. epiphylla species N but different from homologous P. epiphylla species S sequences. Both mitochondria and chloroplasts of P. borealis were thus inherited from one parent- P. epiphylla species N. Studies on 14 different populations of P. borealis gave the same result. These are the first data on organellar transmission in liverworts, the earliest land plants. Moreover, we show that the intron sequences of some organellar genes, until now not used in any systematic studies, could be very good markers in studying taxonomic relationships in closely related species and reconstructing historical events.

Oxidative cleavage of the C-C bond of 3,6-dialkylcyclohexane-1,2-diones by cell suspension cultures of Marchantia polymorpha

Biotransformation of 3,6-dialkylcyclohexane-1,2-diones by cell suspension cultures of Marchantia polymorpha involves regioselective oxidative cleavage of the C-C bond to give the corresponding oxocarboxylic acids shortened by one carbon unit. In the case of cyclohexane-1,2-dione, adipic acid was obtained.