Talks

Tuesday 14th July 2015

Diversity of complex thalloid liverworts (1)
Long, David G.
Royal Botanic Gardens Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, Scotland

A short survey is presented of the five orders and twenty families of complex thalloid liverworts. Using selected representatives of the 36 accepted genera, the range of morphological diversity in vegetative and reproductive gametophytic structures is illustrated as well as diversity of spore ornamentation. Eleven of the families contain only a single genus. The most species-rich genera are Riccia in Ricciaceae and Asterella in Aytoniaceae 

Amphitropical disjunctions in the complex thalloids (2)
Gradstein, Robbert
Muséum National d’Histoire Naturelle, Paris, France

Plant disjunctions between the temperate regions of the northern and southern hemisphere, commonly called amphitropical or bipolar disjunctions, have been discussed by numerous authors but very little attention has been paid to the occurrence of such disjunct distributions in the complex thalloids. A perusal of the literature revealed nineteen species in seven genera (Asterella, Clevea, Corsinia, Oxymitra, Riccia, Riella, Sphaerocarpos) of Marchantiopsida with amphitropical ranges. All of them are distributed in subtropical and mediterranean regions of the northern and southern hemisphere but not (or very rarely) in the Tropics. The majority of the species are disjunct between North and South America, few are disjunct between Eurasia and southern Africa or Australia. The disjunct ranges are generally based on morphological evidence; none have been tested using molecular data. The application of modern molecular and phylogenetic methods to the study of amphitropical ranges in the complex thalloids should be a fruitful approach for future study.

 The beginnings of microtranscriptome evolution in plants : a case study of liverwort Pellia endiviifolia (3)
Pietrykowska, Halina1, Paweł Piszczałka1, Sylwia Alaba2, Andrzej Pacak1, Izabela Sierocka1, Przemyslaw Nuc1, Kashmir Singh1, Patrycja Plewka1, Aleksandra Sulkowska1, Artur Jarmolowski1, Wojciech M Karlowski2, Zofia Szweykowska-Kulinska1,2
1 Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Poznan, Poland
2 Laboratory of Computational Genomics, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Poznan, Poland

MicroRNAs are important regulatory elements of eukaryotic gene expression. These short (18-24 nt) molecules act post-transcriptionally by sequence-specific guidance of RNA Induced Silencing Complex (RISC) to complementary mRNAs which results in slicing or translation inhibition of targeted mRNAs. We applied the high-throughput sequencing technique (SOLEXA, Illumina) and sequenced sRNAs, transcriptome, and degradome from the dioecious liverwort Pellia endiviifolia. 311 miRNA families of conservative miRNA that are identical to model moss Physcomitrella patens and/or other land plants miRNAs were identified. Interestingly, three of the liverwort miRNAs show high similarity to previously reported miRNAs from Chlamydomonas reinhardtii. We confirmed the presence of selected C. reinhardtii miRNAs   by northern hybridization using RNA isolated from P. endiviifolia in vitro plants. Also, the presence of selected conservative miRNAs with homologs in higher land plants identified in P. endiviifolia was confirmed by northern hybridization. Using bioinformatic approaches we studied also novel potential miRNA for P. endiviifolia. 42 new liverwort-specific miRNAs were discovered. Analysis of P. endiviifolia transcriptome revealed the presence of at least twenty putative miRNA precursors. Ten of them were verified using experimental approaches (RACE and genome walking) resulting in establishing the gene structure of the first known liverwort MIR genes and their primary transcripts. Four of identified MIR genes contain one or more introns. The RNA degradome analysis revealed that target mRNAs of only three miRNAs (miR160, miR166, and miR408) have been conserved between liverworts and other land plants. New targets were identified for the remaining conserved miRNAs. Moreover, the analysis of the degradome permitted the identification of targets for 13 novel liverwort-specific miRNAs. This new data supplement our knowledge and understanding of plant miRNA evolution and represent an interesting example of research case for other scientists.

On Monocarpus (Monocarpaceae, Marchantiopsida), an isolated salt-pan complex thalloid liverwort (4)  
Laura L. Forrest1, Michelle L. Hart1, D.Christine  Cargill2, Josephine Milne3, David G. Long1
1Royal Botanic Gardens Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, Scotland
2Australian National Herbarium Canberra, GPO Box 1600, Canberra, Australia
3Royal Botanic Gardens Melbourne, Australia

The phylogenetic placement of Monocarpus sphaerocarpus (Monocarpaceae), a member of the complex thalloid liverworts with highly specialized morphology presumably related to its saltpan habitat, has been determined based on molecular data.  Within the complex thalloid liverworts, Monocarpus resolves as sister to the Sphaerocarpales clade. Detailed ornamentation of the spores of Monocarpus collections from Australia and South Africa, as revealed by SEM, is reported, and some of the morphological features that unite and separate Monocarpus and the Sphaerocarpales s. str. are discussed.

Sex chromosome evolution in haploid dioecy (5)
Szövényi Peter1, Stuart F. McDaniel2, Adam Payton2, Mariana Ricca 1
1 Institute of Systematic Botany, University of Zurich, Switzerland
2 University of Florida Gainesville, Gainesville, Florida, USA

Bryophytes, especially liverworts, represent an appropriate model system to investigate the evolution of sex chromosomes and sex determination in haploid dioecy. In particular, genomic data available for Marchantia polymorpha and related species provides a unique opportunity to resolve these long-standing evolutionary issues at the genomic scale. Our group is using M. polymorpha as a model system to study two major questions surrounding the topics of sex determination and the evolution of sex chromosomes in haploid dioecy. The projects and the approach we are following are discussed in details below.

(I.) In diploid dioecious diploid organisms, where sex determination is governed by dimorphic sex chromosomes, sex chromosomes are expected to differ in genetic variability, size, gene content and gene expression due to asymmetric heterozygosity and suppression of recombination. By contrast, in haploid dioecy, sex chromosomes are equally heterozygous and show suppressed recombination in a similar extent. Therefore, if sex-specific evolutionary forces are negligible, sex chromosomes under haploid dioecy are expected to be influenced by similar evolutionary forces and should follow similar evolutionary trajectories. Nevertheless, experimental evidence contradicts this hypothesis in several aspects and suggests that U and V chromosomes differ in size, gene content and level of degeneration. Therefore, we aim to understand in what extent and why evolutionary trajectories of sex chromosomes under haploid dieocy deviate from theoretical predictions.

(II.) Dioecy is also assumed to be the ancestral condition in liverworts. In line with that, U and V sex chromosomes of Marchantia appear to be considerably old suggested by their gene content and genetic divergence. However, whether the sex determination system and U/V sex chromosomes have evolved only once or multiple times independently is not known. Importantly, abrupt changes from dioecy to monoecy have occurred multiple times and independently during the phylogenetic history of liverworts suggesting that the sex determination system may be labile and might have evolved multiple times. Therefore, it is currently unknown whether U and V chromosomes have evolved multiple times from the very same autosomes in all liverworts and what sort of genomic changes have contributed to the sudden switch in mating system along the liverwort phylogeny. In this second research direction we are investigating the genomic changes that have accompanied the dioecy-monoecy transition which will inform us on the general rules governing sex determination and sex chromosome evolution in haploid dioecy.

We are currently conducting two major experiments that correspond to the two research directions outlined above. In the first experiment we are analyzing the genetic constitution (GBS), sex and phenotypic traits of approx. 200 segregants (single spore isolates) generated by crossing Tak1 and a local Swiss strain of M. polymorpha. With this experiment we aim to identify genes linked to the U and V chromosomes with high confidence. To contrast the molecular evolution of sex- and autosome-linked genes we genotype U/V-specific and autosomal genes in a panel of approx. 200 natural isolates collected around the world. To aid SNP discovery we have also re-sequenced both parental strains.

To investigate the second set of questions we are conducting a comparative genomic analysis of Preissia quadrata and M. polymorpha. P. quadrata is a close relative of M. polymorpha but often behaves as a monoicous species, produces both male and female gametangia on the very same thallus. Both species have nine chromosomes and a comparable genome size. We are currently sequencing and analyzing the P. quadrata genome and investigate how sex chromosomes arose in the Marchantia lineage. We intend to identify whether dioecy or monoicy is ancestral to the group and through which genomic processes (chromosomal rearrangements, fusions) sex chromosomes have originated. In the future we are planning to extend our sequencing effort to other liverwort genomes to identify whether the patterns discovered hold in multiple independent lineages of liverworts. 

Food- and water-conducting systems in complex thalloids with sexual reproduction thrown in (6)
Duckett, Jeff, Silvia Pressel
Life Sciences Department, Plants Division, Natural History Museum, Cromwell Road, London, SW7 5BD, England

The very existence, let alone the functional significance, of food- and water-conducting systems in complex thalloid liverworts is poorly appreciated. They are absent from both generations in hornworts and from the sporophytes throughout liverworts.  Bryophyte food- conducting cells are characterised by vesicles, plastids and mitochondria longitudinally aligned along arrays of endoplasmic microtubules and mixing of vacuolar and cytoplasmic contents paralleling the same phenomenon in the sieve elements of tracheophytes. Whereas this cytology is ubiquitous in the stems, sporophytes and rhizoids of bryopsid mosses in liverworts it is restricted to Haplomitrium and several complex families particularly those harbouring fungal symbionts.  Here these cells form a distinctive region in the thalli between the dorsal air chambers and the ventral fungus-containing cells. Their most likely function may be in transporting of photosynthates to the mycobionts.

Water-conducting systems evolved at least three times in both mosses (Takakiopsida, Polytrichopsida and Bryopsida) and liverworts (Haplomitrium, Pallaviciniaceae and Marchantiopsida).  Whereas in the first five groups these comprise perforate or imperforate dead cells with variously thickened walls in the centre of the stems, setae and thalli, water conduction in complex thalloids is via the pegged rhizoids. Though variously enclosed by scales and ‘internalized’ within the grooves in carpocephala stalks, this system is external and thus unique amongst all fossil and extant land plants.  Like hydroids and sieve elements, pegged rhizoids are dead at maturity. Their highly elastic walls and resistance to cavitation maintain functional integrity through periods of desiccation. Dye movement experiments reveal that water moves very effectively along the pegged rhizoids systems and, in carpocephala grooves, at comparable rates to those in moss hydroids. The pegged rhizoid apparatus is not only far more effective than moss hydroids at maintaining  full hydration in complex thalloids but even more remarkably is also vital  to their  extraordinarily effective sexual reproduction.  Our field observations on wild populations of Marchantia have revealed fertilization distances of up to 18m with sporophytes being produced within almost 100% of the perianths whatever the distance from the nearest male plants.  Rain water is rapidly absorbed by the hydrophilic antheridiophore caps and travels down the grooves taking spermatozoids with it. These are then dispersed on surface water films. On reaching the vicinity of female plants the spermatozoids reach the archegonia in the archegoniophore caps via a mixture of chemotaxis and upward water movement between the pegged rhizoids in the carpocephala grooves.

Biosystematics and Ecology of Neotropical Cyathodium (Cyathodiaceae) (7)
Noris Salazar Allen1, Helena Korpelainen2, Clementina Chung1†, N. Gómez1 & N. Rivas1
1Smithsonian Tropical Research Institute, Panama
2Department of Agricultural Sciences, P.O. Box 27 (Latokartanonkaari 5), University of Helsinki, Finland

Cyathodium is a thalloid liverwort with 12 species distributed in the Paleotropics, the Neotropics and one report for northern Italy. The center of diversity appears to be India with eight species. Five species occur in the Neotropics:  C. bischlerianum Salazar Allen, C. cavernarum Kunze, C. foetidissimum Schiffn., C. spruceanum Prosk. and C. steerei Hässel. Three of these are endemic to the Neotropics: C. bischlerianum, C. spruceanum and C. steerei.  The plants grow on soil along riverbanks, caves, bark in forest, rocks around waterfalls or creeks, cement road ditches, floors, stairs, flower pots, sometimes in arable fields in humid places.  They are seasonal plants and are not drought-tolerant but can perennate by ventral tubers. Plants of Cyathodium are characterized by having two layers of cells that cover air chambers separated by vertical rows of cells and opening to the outside by pores. Some species have a multistratose área (e.g., C. steerei), a pseudocosta. Three of Neotropical species are dioicous and two monoicous.    Neotropical species can be distinguished morphological, molecular (nucleotide sequence variation in the nuclear ribosomal DNA región, ITS1-5.8S rRNA-ITS2, for four species)and chemically.  Fresh collections and additional axenic cultures will be started to compare the chemical composition obtained in 2004  with those that will be obtained in 2015, using samples from the same populations tested before.

Wednesday 15th July 2015

An update on the Marchantia genome (8)
Bowman, John1,2,  Sandra K. Floyd1, 2Takayuki Kochi, 2Katsuyuki T. Yamato, 2Kimi Ishizaki, Kerry Berry3, Jerry Jenkins3, Jeremy Schmutz3
1School of Biological Sciences, Monash University, Clayton Campus, Melbourne, Victoria 3800, Australia; 2, Kyoto University, 3US DOE Joint Genome Institute

The origin of land plants was one of the major evolutionary events in the history of planet earth. Experimental, paleontological, and morphological and molecular systematic data all point to the liverworts as being some of the first plants to evolve and colonize the Ordovician landscape. Thus liverworts are a key group to include in any comparative study aimed at understanding the origin and evolution of organisms that now cover much of terrestrial earth. We chose Marchantia polymorpha as a model liverwort due to (1) the slow rate of molecular evolution in the Marchantiopsida, (2) the small genome size of M. polymorpha relative to more basal liverwort taxa (i.e. the genomes of Haplomitrium and Treubia are 10x larger), (3) the availability of genetic tools to manipulate gene function in M. polymorpha, and (4) the ubiquity of M. polymorpha throughout the world and its ease of growth and genetics in laboratory settings. In collaboration with JGI a draft sequence of the Marchantia polymorpha genome was generated. Assemblies using 454 generated sequence had reduced mis-joining of scaffolds relative to assemblies utilizing on paired end Illumina reads, however, the latter provided better coverage and assemblies at some loci at a local level. A unique feature of the M. polymorpha genome relative to those known from other land plants is the paucity of paralogs of genes encoding regulatory molecules, which may be a consequence of the early evolution of dimorphic sex chromosomes in the Marchantiopsida or possibly the Marchantiophyta resulting in a lack of ancient whole genome duplications in liverworts.

Evolution of sexual systems in complex thalloids (9)
Shimamura, Masaki
Department of Biological Science, Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima, 739-8526, Japan

As for a process of fertilization in complex thalloid liverworts, there is a commonly held view that raindrops hit the disk of mature antheridiophore and splashed sperms swim in the water for the archegonia. However, actually, complex thalloid liverworts have evolved more efficient system for fertilization. Many marchantialian liverworts typically discharge the sperm cells into the air from the antheridial disk. Especially in Conocephalum, sperm cells are dispersed over great distances by the wind. Although stalked antheridiophore of Marchantia ooze the sperm cells moderately into the water on the antheridial disk, the bundles of rhizoids seem to work as effective conduits for sperms. The bundles of pegged rhizoids extended continuously from ventral surface of female plants to just beside archegonia through the grooves of the archegoniophore stalk. Sperms were able to move up the grooves by capillary action among the bundles of pegged rhizoids. Successful fertilization was achieved by just adding the sperm suspension to the edge of female plants without direct water-splash from the disk of antheridiophore. The function of the bundles of pegged rhizoids seems to be not only to conduct water and nutrients, but also to absorb and concentrate the sperms around the hanging archegonia on the receptacle of the archegoniophore.

Development and evolution of the plant soil interface (10)
Dolan, Liam
Department of Plant Sciences University of Oxford, OX1 3RB, England

Understanding how gene regulatory networks change during the course evolution is key to understanding the origin of morphological diversity. Tip-growing filamentous cells such as rhizoids and root hairs develop at the interface between land plants and the soil. These cells are important for anchorage and nutrient acquisition in both vascular and non-vascular plants and play important roles in the interaction with soil microflora. These filamentous tip growing cells constituted the entire “rooting” system of early diverging groups of land plants such as liverworts and mosses. Vascular plants subsequently evolved specialized rooting axes – roots – and these are covered in filamentous cells during some time in their life.

To gain insights into the mechanism that controlled the development of the first rooting systems we have been comparing the developmental mechanism that control the development of rhizoids in liverworts and mosses, and root hairs of seed plants. We carried out extensive genetic screens in Marchantia polymorpha and generated genomic resources that we are happy to share with others. We demonstrate that a network of RSL transcription factors controls the development of rhizoids and root hairs in land plants. Marchantia polymorpha rsl1 mutants are rhizoidless and mutations that result in overexpression of RSL1 cause the development of ectopic rhizoids on the dorsal surface of the thallus. Taken together these data suggest that the RSL genes acted in the last common ancestor of the extant land plants.  Furthermore, we demonstrate that RSL genes are also required for the differentiation of epidermis-derived organs called gemmae. Insights into the evolution of these mechanisms illustrate how regulatory networks and their functions can change during the course of land plant evolution.

Scratching the surface: The Marchantia Cuticle (11) 
Brockington, Sam1, Silvia Presel2, Jeffrey G. Duckett2
1Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, England
2Life Sciences Department, Plants Division, Natural History Museum, Cromwell Road, London, SW7 5BD, England

More accurate phylogenetic hypotheses coupled with the development of early land plant model systems have accelerated research into the origin and early evolution of most land plant adaptations. However research into the origin and evolution of the cuticle lags behind. Indeed, even within well-established flowering plant models, our understanding of cuticle genetics is still in its infancy. We have initiated a comparative genetic research program focused on the plant cuticle, to identify the key events that underpin the evolution of the cuticle in land plants. By coupling phylogeny, morphology, functional genetics and physiology, we hope to build a comprehensive picture of cuticle function and evolution in early land plants. Our first step has been to perform detailed descriptions of cuticle formation through the ontogeny of Marchantia polymorpha in order to more accurately evaluate phenotypes in the longer term. Here I present some preliminary findings from this morphological analysis, together with techniques and approaches we have developed to pursue a genetic approaches to cuticle evolution.   

An overview of malagasy Marchantiidae (12)
Reeb, Catherine
Institut de Systématique, Évolution, Biodiversité ISYEB - UMR 7205 - MNHN, UPMC, CNRS, EPHE
Muséum National D'histoire Naturelle 57 rue cuvier, Case postale 39 FRANCE-75005 Paris

Madagascar is an under-explored country from a bryological standpoint and no synthetic study has been attempted on complex thalloid liverworts. I began to explore historical and recent collections in order to make a synthesis of our current knowledge on the Malagasy Marchantiidae. Sixteen taxa are recognized with eight new records for the island. Among the order Marchantiales, the family Ricciaceae has been particularly underexplored, which could explain the difference between the more than fifty species recognized in South Africa and only five species recorded in Madagascar. My research aims at re-examining species delimitation and local endemism  (especially in Ricciaceae), as the starting point to test evolutionary hypotheses about origin and radiation of Malagasy Marchantiidae. 

Fungal associations in complex thalloids (13)
Pressel, Silvia, Jeffrey G. Duckett
Life Sciences Department, Plants Division, Natural History Museum, Cromwell Road, London, SW7 5BD, England

The evolution of fungal symbioses was one of the key events in the colonization of land by plants over 480MYA. Today up to 90% of all land plants, with representatives from every major lineage except mosses, have fungal symbionts.  Because of their sister position to the Haplomitriopsida at the foot of the land plant tree, complex thalloid liverworts are particularly important for furthering understanding of  the evolution and biology of land plant-fungal symbioses, the appreciation of which has undergone seminal shifts over the last five years. Prior to this, extensive ultrastructural data, across both complex and simple thalloid liverworts, appeared to lend unquestioned support to the monolithic paradigm that glomeromycote fungi were the ancestral mycobionts albeit with no functional studies confirming mutualism in these groups. Following the 2011 discovery that the Haplomitriopsida exclusively harbour Mucoromycotina, an earlier fungal lineage than the Glomeromycota, our collaborative multi-disciplinary research is now revealing that associations involving Mucoromycotina and/or Glomeromycota – with both fungal symbionts sometimes co-occurring in the same host (dual partnerships) – are widespread in early divergent lineages of complex thalloids (e.g. Neohodgsonia, Lunularia) whilst more derived groups are either fungus-free (e.g. Riccia, Monocarpus) or Glomeromycota-specific (e.g. Marchantia, Preissia). All associations investigated so far have been shown to be mutualistic, involving reciprocal exchange of organic carbon and nutrients between partners.  However their responses to simulated ancient and modern atmospheric CO2 concentrations vary dramatically: whilst complex thalloids harbouring Mucoromycotina +/- Glomeromycota benefit from lower, near modern-day a[CO2], as is also true of tracheophytes-Glomeromycota partnerships (mycorrhizas), the efficiency of complex-thalloids-Glomeromycota exclusive associations increases considerably under ancient elevated a[CO2].  Although requiring further plant and fungal sampling, our current understanding of the phylogenetic distribution of fungal symbioses in complex thalloids points to the loss of the ancestral Mucoromycotina partnership – with the basal Sphaerocarpales and Blasiales both fungus-free - and the subsequent reacquisition of the same plus Glomeromycota, with dual partnerships being possibly the prevailing symbiotic strategy.  Why more derived clades engage exclusively with Glomeromycota fungi, an apparently ‘losing’ strategy under modern day a[CO2] resulting from the a[CO2] decline in the late Paleozoic, remains conjectural.  Also problematic, given the widespread occurrence of both types of mycobiont in complex thalloids whose cytology of colonization has so far unquestionably been interpreted as typically glomeromycotean, is our understanding of structural differences and/or similarities between different fungal partners – for example are arbuscules the ‘exclusive signature’ of Glomeromycota symbioses?   We will discuss these questions and other wider implications of our research for understanding the evolution and biology of fungal symbioses in land plants. 

RNA sequencing as a method of choice for the identification of genes differentially expressed between male and female gametophytes producing sex organs in simple thalloid liverwort Pellia endiviifolia sp B (14)
Sierocka, Izabela1, Sylwia Alaba2, Wojciech Karłowski2, Zofia Szweykowska-Kulinska1,2
1 Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Poznan, Poland
2 Laboratory of Computational Genomics, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Poznan, Poland

Regulation of gene expression plays a pivotal role in controlling all aspects of multicellular organisms development, including sexual reproduction. In flowering plants a number of genes has been identified which control the transition from vegetative to generative phase of life cycle. Among liverworts, the most basal lineage of bryophytes, there is almost no data about the genes and mechanisms controlling this transition. This fact puts liverworts in critical evolutionary position to investigate the genetic basis of key innovations which allowed them to survive in demanding terrestrial environment and to give fertile offspring. We have chosen Pellia endiviifolia species B, a dioecious liverwort from class Jungermaniopsida to profile the differences in transcripts level between different stages of the male and female thalli development. We applied the next generation sequencing technology to identify genes engaged in the antheridia and archegonia production in P.endiviifolia. RNA-seq was performed using four different developmental stages: the male thalli i) producing or ii) without antheridia, the female thalli iii) producing or iv) without archegonia. For each library over 40 mln reads were generated which were mapped to the reference de novo transcriptome sequencing data of P. endiviifolia. To select genes with the highest differences in expression between the male and female thalli producing/not producing sex organs bioinformatics analyses were performed with criterion log2_fold_change ≥ 10. As a result 72 Differentially Expressed Genes (DEGs) were selected. Out of 10 genes up-regulated in sperm-producing male thalli, 8 are also expressed in the vegetative phase of males thalli. In turn, out of 62 up-regulated genes in archegonia-producing female thalli, 46 are also expressed in the vegetative phase of female growth. To verify the differentially expressed genes selected from the RNA-seq, real-time PCR analysis was performed which validated 9 male and 47 female specifically expressed genes. The most enriched DEGs belong to RNA or DNA binding protein families, serine/threonine-protein phosphatases, LRR receptor-like kinases and ubiquitin protein ligases. 24 DEGs showed no similarity to known proteins or nucleotide sequences, and the lengths of these transcripts reach from ~250 to ~600nt with no putative open reading frames. It cannot be excluded that these transcripts represent non-coding RNAs or represent partial sequences of  untraslated regions of original mRNA molecules what needs to be further investigated.

Our studies provide possibility to learn about the gene expression regulation within the representative of genus Pellia, which is recognized as the one of the most basal lineage of the simple thalloid liverworts. The work was supported by the Foundation for Polish Science,  grant number POMOST/2012-5/7.

Divergence times, evolution of morphological complexity in a lineage with a slow molecular rate (15)
Villarreal A, Juan Carlos 1; Barbara J. Crandall-Stotler2; Michelle L. Hart1; David G. Long1; Laura L. Forrest1,3
1Royal Botanic Gardens Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, Scotland
2Department of Plant Biology, Southern Illinois University, Carbondale, IL, USA

The fossil occurrence of cryptospore dyad and tetrad assemblages signals the formation of a terrestrial flora around 450 million years ago.  Bryophytes (hornworts, liverworts and mosses) are the extant relatives of the colonizing terrestrial flora and hold the morphological and genomic clues to understand the evolutionary pressures faced by the early land colonizers.  The development of genomic resources for the liverwort Marchantia polymorpha, which is emerging as a new model system for evolutionary and synthetic biology, will undoubtedly provide insights to the genetics underpinning land plant structures and the challenges faced by the earlier land colonizers. The complexity of the complex thalloids, a group including the model system organism Marchantia polymorpha, derives from the layered anatomy of the thalloid gametophyte, which is differentiated into a dorsal, nonclorophyllose epidermis, an upper photosynthetic, assimilatory zone, a parenchymatous, non-photosynthetic storage zone, and a ventral epidermis that bears rows of scales and rhizoids. In most genera, the assimilatory zone contains abundant, schizogenously derived air chambers that are confluent with epidermal pores. The complex thalloids are thus one of the earliest land plant lineages to have evolved internalized gas exchange tissues. In order to understand when and where these morphological innovations occurred, it is necessary to resolve the backbone phylogeny of the complex thalloid liverworts. Here, based on a complete generic phylogeny that includes 98 samples representing all 36 genera, a large molecular dataset and a fossil-calibrated timetree we address the morphological and molecular evolution of the group. We address the branching pattern amongst early divergent lineages of complex thalloids, diversification times, rates of evolution and evolution of morphological complexity evolve within Marchantiopsida, in particularly focused on the carpocephalum, air chambers and sexual systems.

Speed talk: Journal of Bryology
Kungu, Elizabeth
Royal Botanic Gardens Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, Scotland
Journal of Bryology exists to promote the scientific study of bryophytes (mosses, peat-mosses, liverworts and hornworts) and to foster understanding of the wider aspects of bryology.

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