How the Genome Is Organized in the Glomeromycota

Teresa E. Pawlowska

doi:10.1128/9781555815837.ch25

Chapter 25 : How the Genome Is Organized in the Glomeromycota

Author: Teresa E. Pawlowska¹

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Affiliations: 1: Department of Plant Pathology, Cornell University, 334 Plant Science Building, Ithaca, NY 14853-5904

Content Type: Monograph

Publication Year: 2007

Category: Fungi and Fungal Pathogenesis

Book DOI: 10.1128/9781555815837

Chapter DOI: 10.1128/9781555815837.ch25

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Abstract:

Arbuscular mycorrhizal (AM) fungi (phylum Glomeromycota) are one of the most important yet least understood groups of soil microorganisms. This chapter discusses recent findings concerning the genome structure in Glomeromycota in the context of the evolutionary theory predictions. The extent of the intraindividual polymorphism of the PLS1 and rRNA genes combined with the uncommonly large genome size estimates available at the time led Pawlowska and Taylor to speculate that genomes of Glomeromycota may be polyploid. A solution to the dilemma of how multiple gene copies are distributed among the nuclei of Glomeromycota is expected to emerge from the complete genome sequence of Glomus intraradices, which is anticipated to be available in 2007. This genome sequence and future projects to sequence genomes of other AM fungi are also likely to shed light on the source of the huge diversity of genome sizes in various species of Glomeromycota that was uncovered recently. To better understand the patterns of the rDNA variation in Glomeromycota, the chapter first explores general mechanisms behind the process of concerted evolution and possible causes of deviations from the molecular pattern of concerted evolution. The conflicting inferences about the genetic makeup and genome structure of Glomeromycota are clearly a reflection of the scarcity of experimental data. Some of the outstanding questions will be resolved by the examination of genome sequence data of representative AM fungi when these become available in the near future.

Citation: Pawlowska T. 2007. How the Genome Is Organized in the Glomeromycota, p 419-430. In Heitman J, Kronstad J, Taylor J, Casselton L (ed), Sex in Fungi. ASM Press, Washington, DC. doi: 10.1128/9781555815837.ch25

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How the Genome Is Organized in the Glomeromycota

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Figure 25.1

Spores of Glomeromycota harbor hundreds of nuclei. (a) Optical section through a spore of Glomus intraradices stained with DAPI (4’, 6’-diamidino-2-phenylindole) to visualize nuclei, scale bar 10 μm; (b) model of homokaryosis; (c) model of heterokaryosis.

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Figure 25.1

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Figure 25.2

A phylogram representing the single most parsimonious tree of the PLS1 variants detected in isolates of G. etunicatum from California (CA-3-5-4, CA-13-4-2, CA-21-1-4, and CA-73-3-4) and Minnesota (MN-14-8). The numbering of variants corresponds to the numbers assigned by Pawlowska and Taylor ( 68 ). Each isolate contains exactly 13 PLS1 variants (variants 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 14 are present in CA-13-4-2, CA-21-1-4, and CA-73-3-4; variants 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 13 are present in CA-3-5-4; and variants 1, 2, 4, 6, 7, 9, 10, 11, 12, 14, 18, 19, and 20 are present in MN-14-8). Numbers above branches indicate bootstrap support values (1,000 replicates).

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Figure 25.2

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