Message - 7th IAL Symposium

The 7 th International Association for Lichenology Symposium 2012
(1B-O5) Submission ID: IAL0145-00001
PELTIGERA LICHEN SYMBIOMES: METAGENOMICS OF A COMPLEX
NATURAL COMMUNITY
Andresson O. 1 , Jónsson Z. O. 1 , Xavier B. B. 1 , Manoharan S. S. 1 , Miao V. 2 , Snaebjarnarson V. 1 , Jonsson H. 1
1 Department of Life and Environmental Sciences, University of Iceland, Reykjavik, Iceland
2 Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada
Genomic analyses of lichens can be carried out in two fundamentally different ways. First, by the classical
approach starting with pure, usually clonal, cultures of the individual symbiotic organisms, an approach which
is essentially the same as generally used in genomics. This works fine if both (or all) symbionts can be cultured.
The second approach starts with field material and the symbiont genomes are analyzed simultaneously. At first
sight this approach appears only slightly more complicated than with the cultured material. In the best case,
there is a fairly even proportion of two genomes, and after assembly of the basic sequence reads, it is simply
a matter of sorting into two bins. In practice, there are several levels of complications. First, there may be more
than two major symbionts, as in the case of tripartite lichens, and they may contribute very different numbers
of genomes, including variable numbers of organelle genomes. Second, as the contributing organisms are not
purely clonal, there may be considerable polymorphism. This complicates genome assembly and annotation,
but can also contribute information on community structure. Third, a variety of microbes are present in natural
lichen communities, both on surfaces and internal. This microbiome can account for a large part of the total
metagenomic DNA, and can be very disperse in terms of taxonomy and clonality. Results and methodology from
the genomic sequencing and analysis of the major components of the Peltigera membranacea and P. malacea
symbiotic genomes, the mycobiont, the Nostoc photobiont, and the microbiome, will be presented as well as
major features of transcriptomic analyses from thallus, rhizines and apothecia. Use of alternative homologs and
differential gene expression in the different tissues yields molecular information on the nature of this widespread
symbiosis, and the genome sequence base provides a platform for a wide range of investigations, e.g. using an
array of molecular markers and transcriptome sequencing of multiple samples.
(1B-O6) Submission ID: IAL0229-00002
DECODING SYMBIOSIS: THE TWO GENOMES OF THE LICHEN CLADONIA GRAYI
Armaleo D. 1 , Mueller O. 1 , Lutzoni F. 1 , Martin F. 2 , Blanc G. 3 , Merchant S. 4 , Collart F. 5
1 Department of Biology, Duke University, Durham, United States
2 Tree-microbe Interactions, Institut National de la Recherche Scientifique, Nancy, France
3 Institut de Microbiologie De La Mediterranee, Aix-Marseille Université, Marseille, France
4 Chemistry and Biochemistry, University of California, L.A., Los Angeles, United States
5 Biosciences, Argonne National Laboratory, Argonne, United States
We analyzed the genomes of the lichen fungus Cladonia grayi (34 Mb) and its alga, Asterochloris sp.
(56 Mb), sequenced using DNA from the isolated symbionts grown in culture. We used several approaches to
distinguish genes relevant to the lichen symbiosis from those not specifically constrained by it. One method
involved searching for genes with a phylogenetic signature characterized by an early burst of positive selection
followed by stabilizing selection. Another was an analysis of gene family expansion and contraction in the symbionts
compared to their phylogenetic relatives. Both fungus and alga contain expanded families of novel proteins
as well as of known proteins. We will focus on specific transcription factors and transporters. Finally, analyses
of global transcriptional changes during early interactions between fungus and alga were combined with gene
family data to further define genes relevant to symbiosis. Specific features will be discussed in detail.
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