Mutualistic fungal endophytes infect many grass species and often confer benefits to the hosts such as reduced herbivory by insects and animals. The physiological interactions between the endophytes and their hosts have not been well characterized. Fungal-secreted proteins are likely to be important components of the interaction. In the interaction between Poa ampla and the endophyte Neotyphodium sp., a fungal -1,6-glucanase is secreted into the apoplast, and activity of the enzyme is detectable in endophyte-infected plants. Sequence analysis indicates the -1,6-glucanase is homologous to enzymes secreted by the mycoparasitic fungi Trichoderma harzianum and Trichoderma virens. DNA gel-blot analysis indicated the -1,6-glucanase was encoded by a single gene. As a secreted protein, the -1,6-glucanase may have a nutritional role for the fungus. In culture, -1,6-glucanase activity was induced in the presence of -1,6-glucans. From RNA gel blots, similar -1,6-glucanases were expressed in tall fescue (Festuca arundinacea Schreb.) and Chewings fescue (Festuca rubra L. subsp. fallax [Thuill] Nyman) infected with the endophyte species Neotyphodium coenophialum and Epichloë festucae, respectively.Fungal endophytes of the genus Neotyphodium (formerly Acremonium; Glenn et al., 1996) infect many grass species, some of which are important turf and forage grasses. The fungi colonize the intercellular spaces of the aerial plant parts but do not invade the plant cells. The endophyte-grass associations are generally considered to be mutualistic symbioses (Clay, 1988). In many associations, the production of alkaloids by the fungus results in reduced herbivory by insects and animals, thus benefiting the host (Breen, 1994;Bush et al., 1997). The fungi benefit from the access to nutrients provided by the plants.Within the past 20 years, considerable knowledge has been gained on the synthesis and effects of alkaloids, the genetics and taxonomic relationships of endophytes, and the ecological effects of endophyte infection (Clay, 1990;Siegel and Schardl, 1991;Schardl, 1996;Bush et al., 1997). The physiological aspects of the endophyte-grass interactions have not, however, been well characterized in any system. We are investigating the physiology of the fungus-grass interaction with the long-range objective of eventually being able to manipulate agriculturally important interactions. We are using the Poa ampla cv Service (big bluegrass)/Neotyphodium sp. interaction as a model system for the grass/fungus interaction (Lindstrom et al., 1993). P. ampla is apomictic, so we have a ready supply of plants of identical genotype. We also have uninfected plants of the identical genotype, which were identified in older seed lots in which the endophyte had lost viability.Almost nothing is known of the proteins relevant to the interaction between the plant hosts and the fungal endophytes. We are interested in fungalsecreted proteins because they are likely to be important components of the mutualistic interaction because they are located at the...
Advances in plant genomics have permitted the analysis of several members of the grass family, including the major domesticated species, and provided new insights into the evolution of the major crops on earth. Two members, colonial bentgrass (Agrostis capillaris L.) and creeping bentgrass (A. stolonifera L.) have only recently been domesticated and provide an interesting case of polyploidy and comparison to crops that have undergone human selection for thousands of years. As an initial step of characterizing these genomes, we have sampled roughly 10% of their gene content, thereby also serving as a starting point for the construction of their physical and genetic maps. Sampling mRNA from plants subjected to environmental stress showed a remarkable increase in transcription of transposable elements. Both colonial and creeping bentgrass are allotetraploids and are considered to have one genome in common, designated the A 2 genome. Analysis of conserved genes present among the ESTs suggests the colonial and creeping bentgrass A 2 genomes diverged from a common ancestor approximately 2.2 million years ago (MYA), thereby providing an enhanced evolutionary zoom in respect to the origin of maize, which formed 4.8 MYA, and tetraploid wheat, which formed only 0.5 MYA and is the progenitor of domesticated hexaploid wheat.
The biosynthesis of many plant secondary compounds involves the methylation of one or more hydroxyl groups, catalyzed by O-methyltransferases (OMTs). Here, we report the characterization of two OMTs, Van OMT-2 and Van OMT-3, from the orchid Vanilla planifolia Andrews. These enzymes catalyze the methylation of a single outer hydroxyl group in substrates possessing a 1,2,3-trihydroxybenzene moiety, such as methyl gallate and myricetin. This is a substrate requirement not previously reported for any OMTs. Based on sequence analysis these enzymes are most similar to caffeic acid O-methyltransferases (COMTs), but they have negligible activity with typical COMT substrates. Seven of 12 conserved substrate-binding residues in COMTs are altered in Van OMT-2 and Van OMT-3. Phylogenetic analysis of the sequences suggests that Van OMT-2 and Van OMT-3 evolved from the V. planifolia COMT. These V. planifolia OMTs are new instances of COMT-like enzymes with novel substrate preferences.
Lineage-specific gene loss is considered one of the processes contributing to speciation and genome diversity. Such gene loss has been inferred from interspecies comparisons of orthologous DNA segments. Examples of intraspecific gene loss are rare. Here we report identification of a gene, designated Crs-1 (creeping specific-1), that appears to be in the process of being lost from heterozygous populations of the species creeping bentgrass (Agrostis stolonifera). The Crs-1 gene encodes a protein with an N-terminal dirigent protein domain and a C-terminal lectin domain and is similar to the maize (Zea mays) β-glucosidase aggregating factor. Most individual creeping bentgrass plants examined are lacking Crs-1. Some individuals are hemizygous for the Crs-1 locus, indicating major haplotype noncolinearity at that locus. Crs-1 was not detected in several other Agrostis species, indicating it is being lost from the genus. The Crs-1 locus in creeping bentgrass provides a rare example of the evolutionary process of gene loss occurring within a plant species.
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