Effects of demographic history on recombination hotspots in soybean.

Recombination is the primary mechanism underlying genetic improvement in populations and allows plant breeders to create new allelic combinations for agronomic improvement. Soybean [Glycine max (L.) Merr.] has gone through multiple genetic bottlenecks that have significantly affected its genetic diversity, linkage disequilibrium, and altered allele frequencies. To investigate the impact of genetic bottlenecks on recombination hotspots in soybeans, historical recombination was studied in three soybean populations. The populations were wild soybean [Glycine soja (Sieb. and Zucc.)], landraces, and North American elite soybean cultivars that have been genotyped with the SoySNP50K BeadChip. While each population after a genetic bottleneck had an increased average haplotype block size, they did not have a significant difference in the number of hotspots between each population. Instead, the increase in observed haplotype block size is likely due to an elimination of individuals that contained historical recombination at hotspots which decreased the observed rate of recombination for the hotspot after each genetic bottleneck. Conversely, heterochromatic DNA which has an increased haplotype block size compared to euchromatic DNA had a significantly different number of hotspots but not a significant difference in the average hotspot recombination rate. Previously identified genomic motifs associated with hotspots were also associated with hotspots found in the historical populations suggesting a common mechanism. This characterization of historical recombination hotspots in soybeans provides further insights into the effect genetic bottlenecks and selection have on recombination hotspots.

Interspecific and intraspecific transference of metabolism-based mesotrione resistance in dioecious weedy Amaranthus.

Pollen-mediated gene flow (PMGF) might play an important role in dispersing herbicide resistance alleles in dioecious weedy Amaranthus species. Field experiments in a concentric donor-receptor design were conducted to quantify two sets of PMGF studies, an interspecific (Amaranthus tuberculatus × Amaranthus palmeri) and an intraspecific (A. tuberculatus × A. tuberculatus). In both studies, PMGF was evaluated using a resistant A. tuberculatus phenotype with enhanced mesotrione detoxification via P450 enzymes as a source of resistance alleles. For interspecific hybridization, more than 104 000 putative hybrid seedlings were screened with three markers, one phenotypic and two molecular. The two molecular markers used, including 2-bp polymorphisms in the internal transcribed spacer region, distinguished A. palmeri, A. tuberculatus and their hybrids. Results showed that 0.1% hybridization between A. tuberculatus × A. palmeri occurred under field research conditions. For intraspecific hybridization, 22 582 seedlings were screened to assess the frequency of gene flow. The frequency of gene flow (FGF ) varied with distance, direction and year of the study. The farthest distance for 90% reduction of FGF was at 69 m in 2015 however, after averaging across directions it was 13.1 and 26.1 m in 2014 and 2015, respectively. This study highlights the transfer of metabolism-based mesotrione resistance from A. tuberculatus to A. palmeri under field research conditions. The results presented here might aid in the rapid detection of A. palmeri among other Amaranthus species and show that PMFG could be expediting the increase of herbicide resistance in A. palmeri and A. tuberculatus across US crop production areas.

Transcriptional analysis of defense mechanisms in upland tetraploid switchgrass to greenbugs.

BACKGROUND: Aphid infestation of switchgrass (Panicum virgatum) has the potential to reduce yields and biomass quality. Although switchgrass-greenbug (Schizaphis graminum; GB) interactions have been studied at the whole plant level, little information is available on plant defense responses at the molecular level. RESULTS: The global transcriptomic response of switchgrass cv Summer to GB was monitored by RNA-Seq in infested and control (uninfested) plants harvested at 5, 10, and 15 days after infestation (DAI). Differentially expressed genes (DEGs) in infested plants were analyzed relative to control uninfested plants at each time point. DEGs in GB-infested plants induced by 5-DAI included an upregulation of reactive burst oxidases and several cell wall receptors. Expression changes in genes linked to redox metabolism, cell wall structure, and hormone biosynthesis were also observed by 5-DAI. At 10-DAI, network analysis indicated a massive upregulation of defense-associated genes, including NAC, WRKY, and MYB classes of transcription factors and potential ancillary signaling molecules such as leucine aminopeptidases. Molecular evidence for loss of chloroplastic functions was also detected at this time point. Supporting these molecular changes, chlorophyll content was significantly decreased, and ROS levels were elevated in infested plants 10-DAI. Total peroxidase and laccase activities were elevated in infested plants at 10-DAI relative to control uninfested plants. The net result appeared to be a broad scale defensive response that led to an apparent reduction in C and N assimilation and a potential redirection of nutrients away from GB and towards the production of defensive compounds, such as pipecolic acid, chlorogenic acid, and trehalose by 10-DAI. By 15-DAI, evidence of recovery in primary metabolism was noted based on transcript abundances for genes associated with carbon, nitrogen, and nutrient assimilation. CONCLUSIONS: Extensive remodeling of the plant transcriptome and the production of ROS and several defensive metabolites in an upland switchgrass cultivar were observed in response to GB feeding. The early loss and apparent recovery in primary metabolism by 15-DAI would suggest that these transcriptional changes in later stages of GB infestation could underlie the recovery response categorized for this switchgrass cultivar. These results can be exploited to develop switchgrass lines with more durable resistance to GB and potentially other aphids.

Transcriptome profiling of Kentucky bluegrass (Poa pratensis L.) accessions in response to salt stress.

BACKGROUND: Kentucky bluegrass (Poa pratensis L.) is a prominent turfgrass in the cool-season regions, but it is sensitive to salt stress. Previously, a relatively salt tolerant Kentucky bluegrass accession was identified that maintained green colour under consistent salt applications. In this study, a transcriptome study between the tolerant (PI 372742) accession and a salt susceptible (PI 368233) accession was conducted, under control and salt treatments, and in shoot and root tissues. RESULTS: Sample replicates grouped tightly by tissue and treatment, and fewer differentially expressed transcripts were detected in the tolerant PI 372742 samples compared to the susceptible PI 368233 samples, and in root tissues compared to shoot tissues. A de novo assembly resulted in 388,764 transcripts, with 36,587 detected as differentially expressed. Approximately 75 % of transcripts had homology based annotations, with several differences in GO terms enriched between the PI 368233 and PI 372742 samples. Gene expression profiling identified salt-responsive gene families that were consistently down-regulated in PI 372742 and unlikely to contribute to salt tolerance in Kentucky bluegrass. Gene expression profiling also identified sets of transcripts relating to transcription factors, ion and water transport genes, and oxidation-reduction process genes with likely roles in salt tolerance. CONCLUSIONS: The transcript assembly represents the first such assembly in the highly polyploidy, facultative apomictic Kentucky bluegrass. The transcripts identified provide genetic information on how this plant responds to and tolerates salt stress in both shoot and root tissues, and can be used for further genetic testing and introgression.

Transcriptional Profiling of Resistant and Susceptible Buffalograsses in Response to Blissus occiduus (Hemiptera: Blissidae) Feeding.

Understanding plant resistance mechanisms at a molecular level would provide valuable insights into the biological pathways impacted by insect feeding, and help explain specific plant tolerance mechanisms. As a first step in this process, we conducted next-generation sequencing using RNA extracted from chinch bug-tolerant and -susceptible buffalograss genotypes at 7 and 14 d after chinch bug feeding. Sequence descriptions and gene ontology terms were assigned to 1,701 differentially expressed genes. Defense-related transcripts were differentially expressed within the chinch bug-tolerant buffalograss, Prestige, and susceptible buffalograss, 378. Interestingly, four peroxidase transcripts had higher basal expression in tolerant control plants compared with susceptible control plants. Defense-related transcripts, including two peroxidase genes, two catalase genes, several cytochrome P450 transcripts, a glutathione s-transferase, and a WRKY gene were upregulated within the Prestige transcriptome in response to chinch bug feeding. The majority of observed transcripts with oxidoreductase activity, including nine peroxidase genes and a catalase gene, were downregulated in 378 in response to initial chinch bug feeding. The observed difference in transcript expression between these two buffalograss genotypes provides insight into the mechanism(s) of resistance, specifically buffalograss tolerance to chinch bug feeding.

Morphology and Proteome Characterization of the Salivary Glands of the Western Chinch Bug (Hemiptera: Blissidae).

The western chinch bug, Blissus occiduus Barber, is a serious pest of buffalograss, Buchloe dactyloides (Nuttall) due to physical and chemical damage caused during the feeding process. Although previous work has investigated the feeding behaviors of chinch bugs in the Blissus complex, no study to date has explored salivary gland morphology and the associated salivary complex of this insect. Whole and sectioned B. occiduus salivary glands were visualized using light and scanning electron microscopy to determine overall structure and cell types of the salivary glands and their individual lobes. Microscopy revealed a pair of trilobed principal glands and a pair of tubular accessory glands of differing cellular types. To link structure with function, the salivary gland proteome was characterized using liquid chromatography tandem mass spectrometry. The salivary proteome analysis resulted in B. occiduus sequences matching 228 nonhomologous protein sequences of the pea aphid, Acyrthosiphon pisum (Harris), with many specific to the proteins present in the salivary proteome of A. pisum. A number of sequences were assigned the molecular function of hydrolase and oxido-reductase activity, with one specific protein sequence revealing a peroxidase-like function. This is the first study to characterize the salivary proteome of B. occiduus and the first of any species in the family Blissidae.

Transcriptomic and physiological characterization of the fefe mutant of melon (Cucumis melo) reveals new aspects of iron-copper crosstalk.

Iron (Fe) and copper (Cu) homeostasis are tightly linked across biology. In previous work, Fe deficiency interacted with Cu-regulated genes and stimulated Cu accumulation. The C940-fe (fefe) Fe-uptake mutant of melon (Cucumis melo) was characterized, and the fefe mutant was used to test whether Cu deficiency could stimulate Fe uptake. Wild-type and fefe mutant transcriptomes were determined by RNA-seq under Fe and Cu deficiency. FeFe-regulated genes included core Fe uptake, metal homeostasis, and transcription factor genes. Numerous genes were regulated by both Fe and Cu. The fefe mutant was rescued by high Fe or by Cu deficiency, which stimulated ferric-chelate reductase activity, FRO2 expression, and Fe accumulation. Accumulation of Fe in Cu-deficient plants was independent of the normal Fe-uptake system. One of the four FRO genes in the melon and cucumber (Cucumis sativus) genomes was Fe-regulated, and one was Cu-regulated. Simultaneous Fe and Cu deficiency synergistically up-regulated Fe-uptake gene expression. Overlap in Fe and Cu deficiency transcriptomes highlights the importance of Fe-Cu crosstalk in metal homeostasis. The fefe gene is not orthologous to FIT, and thus identification of this gene will provide clues to help understand regulation of Fe uptake in plants.

Development of SCAR markers and UP-PCR cross-hybridization method for specific detection of four major subgroups of Rhizoctonia from infected turfgrasses.

A rapid identification assay for Waitea circinata (anamorph: Rhizoctonia spp.) varieties zeae and circinata causing patch diseases on turfgrasses was developed based on the universally primed PCR (UP-PCR) products cross-blot hybridization. Tester isolates belonging to the two varieties of W. circinata were amplified with a single UP primer L21, which generated multiple DNA fragments for each variety. Probes were prepared with UP-PCR products of each tester isolate by labeling with digoxigenin. Fieldcollected W. circinata isolates and representative isolates of different R. solani anastomosis groups (AG) and AG subgroups were amplified with L21, immobilized on nylon membrane and cross hybridized with the two probes. Isolates within a W. circinata variety cross-hybridized strongly, while non-homologous isolates did not cross-hybridize or did so weakly. Closely related W. circinata varieties zeae and circinata were clearly distinguished with this assay. Sequence-characterized amplified region (SCAR) markers also were developed from UP-PCR products to identify isolates of Thanatephorus cucumeris (anamorph: R. solani) AG 1-IB and AG 2-2IIIB. These two AGs are commonly isolated from diseased, cool-season turfgrasses. The specific SCAR markers that were developed could differentiate isolates of AG 1-IB or AG 2-2IIIB groups. These SCAR markers did not amplify a product from genomic DNA of nontarget isolates of Rhizoctonia. The specificities and sensitivities of the SCAR primers were tested on total DNA extracted from several field-grown, cool-season turf species having severe brown-patch symptoms. First, the leaf samples from diseased turf species were tested for the anastomosis groups of the causal pathogen, and thereafter the total DNA was amplified with the specific primers. The specific primers were sensitive and unique enough to produce a band from total DNA of diseased turfgrasses infected with either AG 1-IB or AG 2-2IIIB.

Porocercospora seminalis gen. et comb. nov., the causal organism of buffalograss false smut.

False smut caused by Cercospora seminalis is an important disease of buffalograss (Buchloë dactyloides) affecting seed production. The pathogen prevents normal caryopsis development and causes considerable yield loss and reduced seed germination. The current taxonomic placement of the false-smut causal pathogen in the genus Cercospora is incorrect based on its morphological characteristics and DNA phylogeny. In the present study the phylogenetic position of C. seminalis is clarified based on DNA sequence analysis of three loci namely the internal transcribed spacer (ITS) region, partial nuclear ribosomal large subunit (LSU) and partial sequences of the RNA polymerase II second largest subunit (RPB2). A collection of C. seminalis isolates was made from buffalograss sites near Lincoln, Nebraska. DNA sequence data indicated that Cercospora seminalis is phylogenetically close to but distinct from species of Bipolaris and Curvularia (Pleosporaceae, Pleosporales). Cercospora seminalis morphologically had unique characteristics, namely densely aggregated and repeatedly branched conidiophores arising from a brown stroma, monotretic conidiogenous cells with inconspicuous loci, and scolecosporous conidia with distosepta, and thickened, darkened hila. Porocercospora is introduced as a new genus to accommodate the buffalograss false-smut pathogen.

Transcriptome analysis of two buffalograss cultivars.

BACKGROUND: Buffalograss [Buchloë dactyloides (Nutt.) Engel. syn. Bouteloua dactyloides (Nutt.) Columbus] is a United States native turfgrass species that requires less irrigation, fungicides and pesticides compared to more commonly used turfgrass species. In areas where water is limited, interest in this grass species for lawns is increasing. While several buffalograss cultivars have been developed through buffalograss breeding, the timeframe for new cultivar development is long and is limited by a lack of useful genetic resources. Two high throughput next-generation sequencing techniques were used to increase the genomic resources available for buffalograss. RESULTS: Total RNA was extracted and purified from leaf samples of two buffalograss cultivars. '378' and 'Prestige' cDNA libraries were subjected to high throughput sequencing on the Illumina GA and Roche 454 Titanium FLX sequencing platforms. The 454 platform (3 samples) produced 1,300,885 reads and the Illumina platform (12 samples) generated approximately 332 million reads. The multiple k-mer technique for de novo assembly using Velvet and Oases was applied. A total of 121,288 contigs were assembled that were similar to previously reported Ensembl commelinid sequences. Original Illumina reads were also mapped to the high quality assembly to estimate expression levels of buffalograss transcripts. There were a total of 325 differentially expressed genes between the two buffalograss cultivars. A glycosyl transferase, serine threonine kinase, and nb-arc domain containing transcripts were among those differentially expressed between the two cultivars. These genes have been previously implicated in defense response pathways and may in part explain some of the performance differences between 'Prestige' and '378'. CONCLUSIONS: To date, this is the first high throughput sequencing experiment conducted on buffalograss. In total, 121,288 high quality transcripts were assembled, significantly expanding the limited genetic resources available for buffalograss genetic studies. Additionally, 325 differentially expressed sequences were identified which may contribute to performance or morphological differences between 'Prestige' and '378' buffalograss cultivars.

Expression profiling of four defense-related buffalograss transcripts in response to chinch bug (Hemiptera: Blissidae) feeding.

Oxidative enzymes are one of many key players in plant tolerance responses and defense signaling pathways. This study evaluated gene expression of four buffalograss transcripts (two peroxidases, a catalase, and a GRAS (gibberellic acid insensitive [GAI], repressor of GAI, and scarecrow) and total peroxidase activity in response to western chinch bug (Blissus occiduus Barber) feeding in susceptible and resistant buffalograsses (Buchloë dactyloides (Nuttall) Engelmann). Basal levels of all four transcripts were consistently higher in the resistant buffalograss when compared with the susceptible genotype, which suggests important physiological differences exist between the two buffalograsses. The four defense-related transcripts also showed differential expression between infested and control plants for both the resistant and susceptible buffalograsses. Differences in total peroxidase activity were also detected between control and infested plants, and basal peroxidase activity was higher in the resistant genotype. Overall, this study indicates that elevated basal levels of specific peroxidases, catalases, and GRAS may be an effective buffalograss defense strategy against chinch bug feeding and other similar biotic stresses.

Recombination hotspots in soybean [Glycine max (L.) Merr.].

Recombination allows for the exchange of genetic material between two parents, which plant breeders exploit to make improved cultivars. This recombination is not distributed evenly across the chromosome. Recombination mostly occurs in euchromatic regions of the genome and even then, recombination is focused into clusters of crossovers termed recombination hotspots. Understanding the distribution of these hotspots along with the sequence motifs associated with them may lead to methods that enable breeders to better exploit recombination in breeding. To map recombination hotspots and identify sequence motifs associated with hotspots in soybean [Glycine max (L.) Merr.], two biparental recombinant inbred lines populations were genotyped with the SoySNP50k Illumina Infinium assay. A total of 451 recombination hotspots were identified in the two populations. Despite being half-sib populations, only 18 hotspots were in common between the two populations. While pericentromeric regions did exhibit extreme suppression of recombination, 27% of the detected hotspots were located in the pericentromeric regions of the chromosomes. Two genomic motifs associated with hotspots are similar to human, dog, rice, wheat, drosophila, and arabidopsis. These motifs were a CCN repeat motif and a poly-A motif. Genomic regions spanning other hotspots were significantly enriched with the tourist family of mini-inverted-repeat transposable elements that resides in <0.34% of the soybean genome. The characterization of recombination hotspots in these two large soybean biparental populations demonstrates that hotspots do occur throughout the soybean genome and are enriched for specific motifs, but their locations may not be conserved between different populations.

Development of molecular inversion probes for soybean progeny genomic selection genotyping.

Increasing rate of genetic gain for key agronomic traits through genomic selection requires the development of new molecular methods to run genome-wide single-nucleotide polymorphisms (SNPs). The main limitation of current methods is the cost is too high to screen breeding populations. Molecular inversion probes (MIPs) are a targeted genotyping-by-sequencing (GBS) method that could be used for soybean [Glycine max (L.) Merr.] that is both cost-effective, high-throughput, and provides high data quality to screen breeder's germplasm for genomic selection. A 1K MIP SNP set was developed for soybean with uniformly distributed markers across the genome. The SNPs were selected to maximize the number of informative markers in germplasm being tested in soybean breeding programs located in the northern-central and middle-southern regions of the United States. The 1K SNP MIP set was tested on diverse germplasm and a recombinant inbred line (RIL) population. Targeted sequencing with MIPs obtained an 85% enrichment for the targeted SNPs. The MIP genotyping accuracy was 93% overall, whereas homozygous call accuracy was 98% with <10% missing data. The accuracy of MIPs combined with its low per-sample cost makes it a powerful tool to enable genomic selection within soybean breeding programs.

Two fingerprinting sets for Humulus lupulus based on KASP and microsatellite markers.

Verification of clonal identity of hop (Humulus lupulus L.) cultivars within breeding programs and germplasm collections is vital to conserving genetic resources. Accurate and economic DNA-based tools are needed in dioecious hop to confirm identity and parentage, neither of which can be reliably determined from morphological observations. In this study, we developed two fingerprinting sets for hop: a 9-SSR fingerprinting set containing high-core repeats that can be run in a single PCR reaction and a kompetitive allele specific PCR (KASP) assay of 25 single nucleotide polymorphisms (SNPs). The SSR set contains a sex-linked primer pair, HI-AGA7, that was used to genotype 629 hop accessions from the US Department of Agriculture (USDA) National Clonal Germplasm Repository (NCGR), the USDA Forage Seed and Cereal Research (FSCR), and the University of Nebraska-Lincoln (UNL) collections. The SSR set identified unique genotypes except for 89 sets of synonymous samples. These synonyms included: cultivars with different designations, the same cultivars from different sources, heat-treated clones, and clonal variants. Population structure analysis clustered accessions into wild North American (WNA) and cultivated groups. Diversity was slightly higher in the cultivated samples due to larger sample size. Parentage and sib-ship analyses were used to identify true-to-type cultivars. The HI-AGA7 marker generated two male- and nine female-specific alleles among the cultivated and WNA samples. The SSR and KASP fingerprinting sets were compared in 190 samples consisting of cultivated and WNA accession for their ability to confirm identity and assess diversity and population structure. The SSR fingerprinting set distinguished cultivars, selections and WNA accessions while the KASP assays were unable to distinguish the WNA samples and had lower diversity estimates than the SSR set. Both fingerprinting sets are valuable tools for identity confirmation and parentage analysis in hop for different purposes. The 9-SSR assay is cost efficient when genotyping a small number of wild and cultivated hop samples (<96) while the KASP assay is easy to interpret and cost efficient for genotyping a large number of cultivated samples (multiples of 96).

Characterization of a Taura syndrome virus isolate originating from the 2004 Texas epizootic in cultured shrimp.

A comprehensive investigation of the Taura syndrome virus (TSV) isolate that caused epizootics in shrimp farms in Texas in 2004 (Texas isolate) revealed that this virus was more virulent in laboratory bioassays than the TSV reference isolate, Hawaii 1994, causing severe symptom development and rapid mortality. Histopathology of moribund animals demonstrated epithelial necrosis within the stomach, appendages, general body cuticle and gills, and the surviving animals demonstrated moderate to numerous lymphoid organ spheroids. Purified virions showed icosahedral morphology, with a diameter of 31 nm. Comparative genome analysis showed that the Texas isolate is more closely related to TSV isolates from Thailand and China than to the Hawaii isolate. The predicted tertiary structures of the inhibition of apoptosis protein (IAP) and protease domains of the Texas isolate are very similar to those of the Hawaii isolate. However, the RNA-dependent RNA polymerase (RdRp) of the Texas isolate has significant structural differences from the Hawaii isolate due to point mutation(s) in the RdRp gene. Changes in the RdRp tertiary structure might contribute to the replication fidelity, virulence and ecological adaptability of the Texas isolate.

Herbicide drift exposure leads to reduced herbicide sensitivity in Amaranthus spp.

While the introduction of herbicide tolerant crops provided growers new options to manage weeds, the widespread adoption of these herbicides increased the risk for herbicide spray drift to surrounding vegetation. The impact of herbicide drift in sensitive crops is extensively investigated, whereas scarce information is available on the consequences of herbicide drift in non-target plants. Weeds are often abundant in field margins and ditches surrounding agricultural landscapes. Repeated herbicide drift exposure to weeds could be detrimental to long-term management as numerous weeds evolved herbicide resistance following recurrent-selection with low herbicide rates. The objective of this study was to evaluate if glyphosate, 2,4-D, and dicamba spray drift could select Amaranthus spp. biotypes with reduced herbicide sensitivity. Palmer amaranth and waterhemp populations were recurrently exposed to herbicide drift in a wind tunnel study over two generations. Seeds from survival plants were used for the subsequent rounds of herbicide drift exposure. Progenies were subjected to herbicide dose-response studies following drift selection. Herbicide drift exposure rapidly selected for Amaranthus spp. biotypes with reduced herbicide sensitivity over two generations. Weed management programs should consider strategies to mitigate near-field spray drift and suppress the establishment of resistance-prone weeds on field borders and ditches in agricultural landscapes.

Aphid-Responsive Defense Networks in Hybrid Switchgrass.

Aphid herbivory elicits plant defense-related networks that are influenced by host genetics. Plants of the upland switchgrass (Panicum virgatum) cultivar Summer can be a suitable host for greenbug aphids (Schizaphis graminum; GB), and yellow sugarcane aphids (Sipha flava, YSA), whereas the lowland cultivar Kanlow exhibited multi-species resistance that curtails aphid reproduction. However, stabilized hybrids of Summer (♀) x Kanlow (♂) (SxK) with improved agronomics can be damaged by both aphids. Here, hormone and metabolite analyses, coupled with RNA-Seq analysis of plant transcriptomes, were utilized to delineate defense networks induced by aphid feeding in SxK switchgrass and pinpoint plant transcription factors (TFs), such as WRKYs that potentially regulate these responses. Abscisic acid (ABA) levels were significantly higher in GB infested plants at 5 and 10 days after infestation (DAI). ABA levels were highest at 15DAI in YSA infested plants. Jasmonic acid levels were significantly elevated under GB infestation, while salicylic acid levels were signifi40cantly elevated only at 15 DAI in YSA infested plants. Similarly, levels of several metabolites were altered in common or specifically to each aphid. YSA infestation induced a significant enrichment of flavonoids consistent with an upregulation of many genes associated with flavonoid biosynthesis at 15DAI. Gene co-expression modules that responded singly to either aphid or in common to both aphids were differentiated and linked to specific TFs. Together, these data provide important clues into the interplay of metabolism and transcriptional remodeling accompanying defense responses to aphid herbivory in hybrid switchgrass.

Response of Amaranthus spp. following exposure to sublethal herbicide rates via spray particle drift.

The adverse consequences of herbicide drift towards sensitive crops have been extensively reported in the literature. However, little to no information is available on the consequences of herbicide drift onto weed species inhabiting boundaries of agricultural fields. Exposure to herbicide drift could be detrimental to long-term weed management as several weed species have evolved herbicide-resistance after recurrent selection with sublethal herbicide rates This study investigated the deposition of glyphosate, 2,4-D, and dicamba spray particle drift from applications with two different nozzles in a low speed wind tunnel, and their impact on growth and development of Amaranthus spp. Herbicide drift resulted in biomass reduction or complete plant mortality. Inflection points (distance to 50% biomass reduction) for Amaranthus tuberculatus were 7.7, 4.0, and 4.1 m downwind distance for glyphosate, 2,4-D, and dicamba applications with the flat-fan nozzle, respectively, whereas these values corresponded to 2.8, 2.5, and 1.9 m for applications with the air-inclusion nozzle. Inflection points for Amaranthus palmeri biomass reduction were 16.3, 10.9, and 11.5 m for glyphosate, 2,4-D, and dicamba applications with the flat-fan nozzle, respectively, whereas these values corresponded to 7.6, 5.4, and 5.4 m for applications with the air-inclusion nozzle. Plants were more sensitive to glyphosate at higher exposure rates than other herbicides, whereas plants were more sensitive to 2,4-D and dicamba at lower exposure rates compared to glyphosate. Applications with the flat-fan nozzle resulted in 32.3 and 11.5% drift of the applied rate at 1.0 and 3.0 m downwind, respectively, whereas the air-inclusion nozzle decreased the dose exposure in the same distances (11.4 and 2.7%, respectively). Herbicide drift towards field boundaries was influenced by nozzle design and exposed weeds to herbicide rates previously reported to select for herbicide-resistant biotypes.

Gene Expression Profiling of Iron Deficiency Chlorosis Sensitive and Tolerant Soybean Indicates Key Roles for Phenylpropanoids under Alkalinity Stress.

Alkaline soils comprise 30% of the earth and have low plant-available iron (Fe) concentration, and can cause iron deficiency chlorosis (IDC). IDC causes soybean yield losses of $260 million annually. However, it is not known whether molecular responses to IDC are equivalent to responses to low iron supply. IDC tolerant and sensitive soybean lines provide a contrast to identify specific factors associated with IDC. We used RNA-seq to compare gene expression under combinations of normal pH (5.7) or alkaline pH (7.7, imposed by 2.5 mM bicarbonate, or pH 8.2 imposed by 5 mM bicarbonate) and normal (25 µM) or low (1 µM) iron conditions from roots of these lines. Thus, we were able to treat pH and Fe supply as separate variables. We also noted differential gene expression between IDC sensitive and tolerant genotypes in each condition. Classical iron uptake genes, including ferric-chelate reductase (FCR) and ferrous transporters, were upregulated by both Fe deficiency and alkaline stress, however, their gene products did not function well at alkaline pH. In addition, genes in the phenylpropanoid synthesis pathway were upregulated in both alkaline and low Fe conditions. These genes lead to the production of fluorescent root exudate (FluRE) compounds, such as coumarins. Fluorescence of nutrient solution increased with alkaline treatment, and was higher in the IDC tolerant line. Some of these genes also localized to previously identified QTL regions associated with IDC. We hypothesize that FluRE become essential at alkaline pH where the classical iron uptake system does not function well. This work could result in new strategies to screen for IDC tolerance, and provide breeding targets to improve crop alkaline stress tolerance.

Transcriptome Profiling of Buffalograss Challenged with the Leaf Spot Pathogen Curvularia inaequalis.

Buffalograss (Bouteloua dactyloides) is a low maintenance U. S. native turfgrass species with exceptional drought, heat, and cold tolerance. Leaf spot caused by Curvularia inaequalis negatively impacts buffalograss visual quality. Two leaf spot susceptible and two resistant buffalograss lines were challenged with C. inaequalis. Samples were collected from treated and untreated leaves when susceptible lines showed symptoms. Transcriptome sequencing was done and differentially expressed genes were identified. Approximately 27 million raw sequencing reads were produced per sample. More than 86% of the sequencing reads mapped to an existing buffalograss reference transcriptome. De novo assembly of unmapped reads was merged with the existing reference to produce a more complete transcriptome. There were 461 differentially expressed transcripts between the resistant and susceptible lines when challenged with the pathogen and 1552 in its absence. Previously characterized defense-related genes were identified among the differentially expressed transcripts. Twenty one resistant line transcripts were similar to genes regulating pattern triggered immunity and 20 transcripts were similar to genes regulating effector triggered immunity. There were also nine up-regulated transcripts in resistance lines which showed potential to initiate systemic acquired resistance (SAR) and three transcripts encoding pathogenesis-related proteins which are downstream products of SAR. This is the first study characterizing changes in the buffalograss transcriptome when challenged with C. inaequalis.