Ivan W. Mott

Production of the alkaloid swainsonine by a fungal endosymbiont of the Ascomycete order Chaetothyriales in the host Ipomoea carnea.

Some plant species within the Convolvulaceae (morning glory family) from South America, Africa, and Australia cause a neurologic disease in grazing livestock caused by swainsonine. These convolvulaceous species including Ipomoea carnea contain the indolizidine alkaloid swainsonine, an inhibitor of α-mannosidase and mannosidase II, and polyhydroxy nortropane alkaloids, the calystegines which are glycosidase inhibitors. Swainsonine has been shown to be produced by a fungal endosymbiont in legumes of the Astragalus and Oxytropis genera, where it causes a similar neurologic disease in grazing livestock called locoism. Here we demonstrate that I. carnea plants are infected with a fungal endosymbiont that was cultured from its seeds and which produced swainsonine in pure culture but not the calystegines. The same fungal endosymbiont was detected by PCR and by culturing in I. carnea plants containing swainsonine. The fungal endosymbiont belongs to the Ascomycete order Chaetothyriales. Plants derived from fungicide-treated seeds lacked swainsonine, but calystegine concentrations were unaltered.

Development and annotation of perennial Triticeae ESTs and SSR markers.

Triticeae contains hundreds of species of both annual and perennial types. Although substantial genomic tools are available for annual Triticeae cereals such as wheat and barley, the perennial Triticeae lack sufficient genomic resources for genetic mapping or diversity research. To increase the amount of sequence information available in the perennial Triticeae, three expressed sequence tag (EST) libraries were developed and annotated for Pseudoroegneria spicata, a mixture of both Elymus wawawaiensis and E. lanceolatus, and a Leymus cinereus x L. triticoides interspecific hybrid. The ESTs were combined into unigene sets of 8 780 unigenes for P. spicata, 11 281 unigenes for Leymus, and 7 212 unigenes for Elymus. Unigenes were annotated based on putative orthology to genes from rice, wheat, barley, other Poaceae, Arabidopsis, and the non-redundant database of the NCBI. Simple sequence repeat (SSR) markers were developed, tested for amplification and polymorphism, and aligned to the rice genome. Leymus EST markers homologous to rice chromosome 2 genes were syntenous on Leymus homeologous groups 6a and 6b (previously 1b), demonstrating promise for in silico comparative mapping. All ESTs and SSR markers are available on an EST information management and annotation database (http://titan.biotec.uiuc.edu/triticeae/).

Production of the alkaloid swainsonine by a fungal endophyte in the host Swainsona canescens.

Legumes belonging to the Astragalus, Oxytropis, and Swainsona genera have been noted by ranchers in the Americas, Asia, and Australia to cause a neurologic disease often referred to as locoism or peastruck. The toxin in these legumes is swainsonine, an α-mannosidase and mannosidase II inhibitor. Recent research has shown that in Astragalus and Oxytropis species swainsonine is produced by a fungal endophyte belonging to the Undifilum genus. Here Swainsona canescens is shown to harbor an endophyte that is closely related to Undifilum species previously cultured from locoweeds of North America and Asia. The endophyte produces swainsonine in vitro and was detected by PCR and culturing in S. canescens. The endophyte isolated from S. canescens was characterized as an Undifilum species using morphological and phylogenetic analyses.

A Y genome specific STS marker in Pseudoroegneria and Elymus species (Triticeae: Gramineae).

The tribe Triticeae Dumortier in the grass family (Poaceae) includes the most important cereal crops (e.g., wheat, barley, and rye) and some economically important forage grasses. Elymus L. is the largest and most complex genus in the Triticeae tribe with approximately 150 species occurring worldwide. The genomic constitutions of approximately 40% of Elymus species are unknown and some have unverified genomic combinations. Of those known for genome constitutions, Elymus species have a genomic formula of StH, StP, StY, StStY, StHY, StPY, or StWY. However, the origin of the Y genome is unknown because no diploid species have been identified as the Y genome donor. A putative Y genome specific random amplified polymorphic DNA (RAPD) marker was converted to a sequence tagged site (STS) marker. The reliability of this STS marker for confirming the presence of the Y genome was demonstrated using 42 accessions of Elymus. The STS-PCR for the Y genome marker was then assayed on 43 accessions of diploid Pseudoroegneria (Nevski) A. Löve species having the St genome to identify possible donors of the Y genome. A rare accession of Pseudoroegneria spicata (Pursh) A. Löve was found to possess sequences that most closely related to those from the tetraploid Elymus longearistatus (Boiss.) Tzvelev (StStYY), making P. spicata the most likely donor of the Y genome, although Pseudoroegneria libanotica (Heck.) D.R. Dewey or other Pseudoroegneria species could not be excluded. Our findings support the hypothesis that the Y genome in some Elymus species shares a progenitor genome (designated StY) with the St genome of Pseudoroegneria.

Genes controlling plant growth habit in Leymus (Triticeae): maize barren stalk1 (ba1), rice lax panicle, and wheat tiller inhibition (tin3) genes as possible candidates

Leymus cinereus and L. triticoides are large caespitose and rhizomatous perennial grasses, respectively. Previous studies detected quantitative trait loci (QTL) controlling rhizome spreading near the viviparous1 (vp1) gene markers on linkage groups LG3a and LG3b in two families, TTC1 and TTC2, derived from Leymus triticoides × Leymus cinereus hybrids. The wheat tiller inhibition gene (tin3) is located on Triticum monococcum chromosome 3 AmL near vp1. Triticeae group 3 is reportedly collinear with rice chromosome 1, which also contains the maize barren stalk1 and rice lax branching orthogene near vp1. However, previous studies lacked cross-species markers for comparative mapping and showed possible rearrangements of Leymus group 3 in wheat-Leymus racemosus chromosome addition lines. Here, we developed expressed sequence tag (EST) markers from Leymus tiller and rhizomes and mapped sequences aligned to rice chromosome 1. Thirty-eight of 44 informative markers detected loci on Leymus LG3a and LG3b that were collinear with homoeologous sequences on rice chromosome 1 and syntenous in homoeologous group 3 wheat-Leymus and wheat-Thinopyrum addition lines. A SCARECROW-like GRAS-family transcription factor candidate gene was identified in the Leymus EST library, which aligns to the Leymus chromosome group 3 growth habit QTL and a 324-kb rice chromosome 1 region thought to contain the wheat tin3 gene.

Characterization of physiological responses of two alfalfa half-sib families with improved salt tolerance

Alfalfa (Medicago sativa L.) is a major forage crop worldwide that is relatively sensitive to soil salinity. Improved cultivars with high production on saline soil will benefit many producers and land managers. This study reports the characterization of physiological responses of two unrelated experimental alfalfa half-sib families, HS-A and HS-B, selected for their improved survival under saline conditions (up to EC 18). Six-week-old plants were subjected to NaCl-nutrient solution treatment for three weeks starting at an electrical conductivity (EC) of 3 dS m(-1) with incremental increases of 3 dS m(-1) every week, reaching 9 dS m(-1) in the third week. HS-B showed greater leaf number (72%) and stem length (44%) while HS-A showed better leaf production (84%) under salt treatment compared to the initial genetic backgrounds from which they were developed. This improved growth is associated with 208% and 78% greater accumulation of chlorophyll content in HS-B and HS-A, respectively. Both HS-A and HS-B also showed improved capability to maintain water content (RWC) under salt stress compared to the initial populations. Differing from its initial populations (P-B), HS-B did not accumulate Na in shoots after salt treatment. HS-B also maintained K(+)/Na(+) and Ca(2+)/Na(+) ratios, while P-B showed 59% and 69% decrease in these ion ratios, respectively. Na(+) content in HS-A was not different from its initial populations (P-A) after salt treatment. However, HS-A showed an enhanced accumulation of Ca(2+) and maintained the levels of Mg(2+) and K(+) in shoots compared to the P-A populations. This study provides physiological support of improved salt tolerance in HS-A and HS-B and suggests that these plants maintain ion homeostasis but have different mechanisms of coping with high salinity.

Genetic Improvement and Diversity in Snake River Wheatgrass (Elymus wawawaiensis) (Poaceae: Triticeae)

Abstract With the increased emphasis on using native plant materials in range revegetation programs in the western United States it is critical to identify genetically similar groups and develop native grasses that are competitive with invasive weeds, easy to establish, and persistent, and that produce high seed yield. A grass that shows appreciable drought tolerance on arid rangelands is Snake River wheatgrass (Elymus wawawaiensis J. Carlson & Barkworth). This study was designed to estimate genetic relationships and underlying genetic components for seed and forage trait improvement between plant introductions (PIs) of Snake River wheatgrass, 28 half-sib Snake River wheatgrass families (HSFs), and cultivars Secar and Discovery at Nephi, Utah, between 2005 and 2006. Based on molecular genetic diversity data in Snake River wheatgrass, with the exception of the PIs originating from Enterprise, Oregon, all other collections and cultivars are not genetically different and represent a common gene pool from which to develop improved Snake River wheatgrass germplasm. Selection in Snake River wheatgrass for total seed yield (g · plot−1), 100-seed weight (g), and seedling emergence from a deep planting depth had a positive effect. Further increases through selection and genetic introgression from hybridization with PIs will likely increase seed yield and 100-seed weight, but will not increase seedling emergence. Increases in dry matter yield (DMY) were observed after two cycles of selection in the HSFs compared to the PIs. There remains considerable genetic and phenotypic variation to further increase DMY in Snake River wheatgrass through selection and hybridization. Trends in forage nutritional quality were not observed after two cycles of selection in the HSFs or the PIs and will not likely result in improvement. Through recurrent selection, populations of Snake River wheatgrass have been and can be developed to more effectively establish and compete on annual weed–infested rangelands.

A molecular genetic linkage map identifying the St and H subgenomes of Elymus (Poaceae: Triticeae) wheatgrass

Elymus L. is the largest and most complex genus in the Triticeae tribe of grasses with approximately 150 polyploid perennial species occurring worldwide. We report here the first genetic linkage map for Elymus. Backcross mapping populations were created by crossing caespitose Elymus wawawaiensis (EW) (Snake River wheatgrass) and rhizomatous Elymus lanceolatus (EL) (thickspike wheatgrass) to produce F(1) interspecific hybrids that were then backcrossed to the same EL male to generate progeny with segregating phenotypes. EW and EL are both allotetraploid species (n = 14) containing the St (Pseudoroegneria) and H (Hordeum) genomes. A total of 387 backcross progeny from four populations were genotyped using 399 AFLP and 116 EST-based SSR and STS markers. The resulting consensus map was 2574 cM in length apportioned among the expected number of 14 linkage groups. EST-based SSR and STS markers with homology to rice genome sequences were used to identify Elymus linkage groups homoeologous to chromosomes 1-7 of wheat. The frequency of St-derived genome markers on each linkage group was used to assign genome designations to all linkage groups, resulting in the identification of the seven St and seven H linkage groups of Elymus. This map also confirms the alloploidy and disomic chromosome pairing and segregation of Elymus and will be useful in identifying QTLs controlling perennial grass traits in this genus.

Characterization of alien chromosomes in backcross derivatives of Triticum aestivum × Elymus rectisetus hybrids by using molecular markers and sequential multicolor FISH/GISH.

Wild Triticeae grasses serve as important gene pools for forage and cereal crops. Based on DNA sequences of genome-specific RAPD markers, sequence-tagged site (STS) markers specific for W and Y genomes have been obtained. Coupling with the use of genomic in situ hybridization, these STS markers enabled the identification of the W- and Y-genome chromosomes in backcross derivatives from hybrids of bread wheat Triticum aestivum L. (2n=42; AABBDD) and Elymus rectisetus (Nees in Lehm.) Á. Löve & Connor (2n=42; StStWWYY). The detection of six different alien chromosomes in five of these derivatives was ascertained by quantitative PCR of STS markers, simple sequence repeat markers, rDNA genes, and (or) multicolor florescence in situ hybridization. Disomic addition line 4687 (2n=44) has the full complement of 42 wheat chromosomes and a pair of 1Y chromosomes that carry genes for resistance to tan spot (caused by Pyrenophora tritici-repentis (Died.) Drechs.) and Stagonospora nodorum blotch (caused by Stagonospora nodorum (Berk.) Castellani and Germano). The disomic addition line 4162 has a pair of 1St chromosomes and 21 pairs of wheat chromosomes. Lines 4319 and 5899 are two triple substitution lines (2n=42) having the same chromosome composition, with 2A, 4B, and 6D of wheat substituted by one pair of W- and two pairs of St-genome chromosomes. Line 4434 is a substitution-addition line (2n=44) that has the same W- and St-genome chromosomes substituting 2A, 4B, and 6D of wheat as in lines 4319 and 5899 but differs by having an additional pair of Y-genome chromosome, which is not the 1Y as in line 4687. The production and identification of these alien cytogenetic stocks may help locate and isolate genes for useful agronomic traits.

Ecotypic Variation in Elymus elymoides subsp. brevifolius in the Northern Intermountain West

Abstract Bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey) is an important native bunchgrass for rangeland restoration in western North America. This species is taxonomically complex and has diverged into as many as four subspecies, including subsp. brevifolius, for which four geographically distinct races have been described (A, B, C, and D). Of these four races, only C occurs in the northern Intermountain West. Our objectives were to describe phenotypic and genetic variation within C and to ascertain its taxonomic status. We evaluated 32 populations of C collected across the northern Intermountain West for a battery of biomass, phenological, and functional traits in common-garden settings in the field and greenhouse. Genetic variation was assessed with the use of amplified fragment length polymorphism (AFLP) markers, and correlations were calculated among phenotypic, genetic, environmental, and geographic distance matrices with the use of Mantel tests. Values for these four distance measures were positively correlated, suggesting that environmental heterogeneity and isolation by distance are shaping ecotypic divergence driven by natural selection. We describe three phenotypic zones for C that correspond to previously established ecoregion boundaries. Because genetic data group C apart from subsp. brevifolius races A, B, and D, which originate in the Rocky Mountains and western Great Plains, the so-called race C merits description as a new subspecies apart from subsp. brevifolius.