Vincent R. Pantalone

Seed quality QTL in a prominent soybean population.

Soybean [Glycine max (L.) Merr.] is a versatile crop due to its multitude of uses as a high protein meal and vegetable oil. Soybean seed traits such as seed protein and oil concentration and seed size are important quantitative traits. The objective of this study was to identify representative protein, oil, and seed size quantitative trait loci (QTL) in soybean. A recombinant inbred line (RIL) population consisting of 131 F6-derived lines was created from two prominent ancestors of North American soybeans (‘Essex’ and ‘Williams’) and the RILs were grown in six environments. One hundred simple sequence repeat (SSR) markers spaced throughout the genome were mapped in this population. There were a total of four protein, six oil, and seven seed size QTL found in this population. The QTL found in this study may assist breeders in marker-assisted selection (MAS) to retain current positive QTL in modern soybeans while simultaneously pyramiding additional QTL from new germplasm.

The low phytic acid phenotype in soybean line CX1834 is due to mutations in two homologs of the maize low phytic acid gene.

Plant seeds accumulate phosphorus in the form of myo‐inositol‐1,2,3,4,5,6‐hexa‐kisphosphate, commonly referred to as phytic acid. Phytic acid is found complexed with cationic mineral species in the form of phytate, which is not well digested or absorbed by monogastric species such as humans, poultry, and swine. As a result, soybean [Glycine max (L.) Merr.] has an effective deficiency of phosphorus and other minerals, despite high levels of minerals and phosphorus in the seed. Excreted phytate can also contribute to phosphorus contamination of groundwater and eutrophication of freshwater lakes and streams. In maize (Zea mays L. ssp. mays), a recessive mutation in a conserved region within the low phytic acid 1 (lpa1) gene is responsible for the low phytic acid phenotype. We have identified recessive mutations in two soybean homologs of the maize lpa1 gene in soybean line CX1834, a mutagenized line with a low phytic acid phenotype. In three populations analyzed, we identified complete association between homozygosity for mutant alleles of the two lpa1 homologs and the low phytic acid phenotype in soybean. Molecular marker assays were designed that can be used to directly select for the mutant alleles that control the phenotype.

Gene expression profiling of resistant and susceptible soybean lines infected with soybean cyst nematode

Soybean cyst nematode (SCN) is the most devastating pathogen of soybean. Information about the molecular basis of soybean–SCN interactions is needed to assist future development of effective management tools against this pathogen. Toward this end, soybean transcript abundance was measured using the Affymetrix Soybean Genome Array in a susceptible and a resistant reaction of soybean to SCN infection. Two genetically related soybean sister lines TN02-226 and TN02-275, which are resistant and susceptible, respectively, to the SCN race 2 infection were utilized in these experiments. Pairwise comparisons followed by false discovery rate analysis indicated that the expression levels of 162 transcripts changed significantly in the resistant line, of which 84 increased while 78 decreased. However, in the susceptible line, 1,694 transcripts changed significantly, of which 674 increased while 1,020 decreased. Comparative analyses of these transcripts indicated that a total of 51 transcripts were in common between resistance and susceptible responses. In this set, 42 transcripts increased in the resistant line, but decreased in the susceptible line. Quantitative real-time reverse-transcription polymerase chain reaction confirmed the results of microarray analysis. Of the transcripts to which a function could be assigned, genes were associated with metabolism, cell wall modification, signal transduction, transcription, and defense. Microarray analyses examining two genetically related soybean lines against the same SCN population provided additional insights into the specific changes in gene expression of a susceptible and a resistant reaction beneficial for identification of genes involved in defense.

Overexpression of a soybean salicylic acid methyltransferase gene confers resistance to soybean cyst nematode

Salicylic acid plays a critical role in activating plant defence responses after pathogen attack. Salicylic acid methyltransferase (SAMT) modulates the level of salicylic acid by converting salicylic acid to methyl salicylate. Here, we report that a SAMT gene from soybean (GmSAMT1) plays a role in soybean defence against soybean cyst nematode (Heterodera glycines Ichinohe, SCN). GmSAMT1 was identified as a candidate SCN defence-related gene in our previous analysis of soybean defence against SCN using GeneChip microarray experiments. The current study started with the isolation of the full-length cDNAs of GmSAMT1 from a SCN-resistant soybean line and from a SCN-susceptible soybean line. The two cDNAs encode proteins of identical sequences. The GmSAMT1 cDNA was expressed in Escherichia coli. Using in vitro enzyme assays, E. coli-expressed GmSAMT1 was confirmed to function as salicylic acid methyltransferase. The apparent Km value of GmSAMT1 for salicylic acid was approximately 46 μM. To determine the role of GmSAMT1 in soybean defence against SCN, transgenic hairy roots overexpressing GmSAMT1 were produced and tested for SCN resistance. Overexpression of GmSAMT1 in SCN-susceptible backgrounds significantly reduced the development of SCN, indicating that overexpression of GmSAMT1 in the transgenic hairy root system could confer resistance to SCN. Overexpression of GmSAMT1 in transgenic hairy roots was also found to affect the expression of selected genes involved in salicylic acid biosynthesis and salicylic acid signal transduction.

Molecular Cloning and Biochemical Characterization of an Endo-β-mannanase Gene from Soybean for Soybean Meal Improvement

Soybean meal is the most commonly used protein source in animal feeds. Among the undesirable attributes of soybean meal is the high level of β-mannan, which was determined to be detrimental to the growth performance of animals. β-Mannan is a type of hemicellulose in the plant cell wall and can be hydrolyzed by endo-β-mannanase. The goal of this study is to isolate and characterize an endo-β-mannanase gene from soybean that can be used for genetic improvement of soybean meal. From the sequenced soybean genome, 21 putative endo-β-mannanase genes were identified. On the basis of their relatedness to known functional plant endo-β-mannanases, four soybean endo-β-mannanase genes (GmMAN1 to GmMAN4) were chosen for experimental analysis. GmMAN1 and GmMAN4 showed expression in the soybean tissue examined, and their cDNAs without the sequences for signal peptide were cloned and expressed in Escherichia coli to produce recombinant enzymes. Only GmMAN1 showed endo-β-mannanase hydrolase activity. Further gene expression analysis showed that GmMAN1 is specifically expressed in cotyledons of seedlings, suggesting a role of GmMAN1 in degrading mannan-rich food reserves during soybean seedling establishment. Purified recombinant GmMAN1 exhibited an apparent K(m) value of 34.9 mg/mL. The catalytic efficiency (k(cat)/K(m)) of GmMAN1 was determined to be 0.7 mL/(mg·s). GmMAN1 was also shown to be active in hydrolyzing the β-mannan-rich cell wall of soybean seeds.

Soybean Seed Amino Acid Content QTL Detected Using the Uni- versal Soy Linkage Panel 1.0 with 1,536 SNPs

1 Current address: Clemson Pee Dee REC, Advanced Plant Technology Center, 2200 Pocket Road, Florence, SC 29506, USA; 2 University of Tennessee, Department of Plant Sciences, 2431 Joe Johnson Dr., Knoxville, TN 37996, USA; 3 Monsanto, 140 W. Industrial Drive, Harrisburg, SD 57032, USA; 4 University of Arkansas, Department of Crop, Soil, and Environmental Sciences, Fayetteville, AR 72701, USA; 5 Southern Illinois University, Department of Plant, Soil Science and Agricultural Systems, 1205 Lincoln Drive, Carbondale, IL 62901, USA; 6 Soybean Genomics and Improvement Laboratory, Beltsville Agricultural Research Center – West, USDA, ARS, Beltsville, MD 20705, USA; 7 Current address: DuPont Pioneer, 8305 NW 62nd Ave., PO Box 7060, Johnston, IA 50131-7060, USA.

Inheritance of red foliage in flowering dogwood (Cornus florida L.)

Flowering dogwood (Cornus florida L.) is an ornamental tree valued for its showy white, pink, or red spring bract display and red fall color. A “pseudo” F2 flowering dogwood population was recently developed from a honeybee mediated cross of ‘Cherokee Brave’xa0×xa0‘Appalachian Spring’. The foliage color of 94 “pseudo” F2 plants segregated into green- and red- leaved phenotypes and was visually rated for color on five spring dates over 3xa0years (2007–2009). Chi-square analyses of observed segregation of phenotypes indicated that a complementary gene interaction form of epistasis controls foliage color with a 9:7 two gene ratio. We propose the symbols rl1 and rl2 for the genes controlling this trait.

An (E,E)‐α‐farnesene synthase gene of soybean has a role in defence against nematodes and is involved in synthesizing insect‐induced volatiles

Summary Plant terpene synthase genes (TPSs) have roles in diverse biological processes. Here, we report the functional characterization of one member of the soybean TPS gene family, which was designated GmAFS. Recombinant GmAFS produced in Escherichia coli catalysed the formation of a sesquiterpene (E,E)‐α‐farnesene. GmAFS is closely related to (E,E)‐α‐farnesene synthase gene from apple, both phylogenetically and structurally. GmAFS was further investigated for its biological role in defence against nematodes and insects. Soybean cyst nematode (SCN) is the most important pathogen of soybean. The expression of GmAFS in a SCN‐resistant soybean was significantly induced by SCN infection compared with the control, whereas its expression in a SCN‐susceptible soybean was not changed by SCN infection. Transgenic hairy roots overexpressing GmAFS under the control of the CaMV 35S promoter were generated in an SCN‐susceptible soybean line. The transgenic lines showed significantly higher resistance to SCN, which indicates that GmAFS contributes to the resistance of soybean to SCN. In soybean leaves, the expression of GmAFS was found to be induced by Tetranychus urticae (two‐spotted spider mites). Exogenous application of methyl jasmonate to soybean plants also induced the expression of GmAFS in leaves. Using headspace collection combined with gas chromatography–mass spectrometry analysis, soybean plants that were infested with T. urticae were shown to emit a mixture of volatiles with (E,E)‐α‐farnesene as one of the most abundant constituents. In summary, this study showed that GmAFS has defence roles in both below‐ground and above‐ground organs of soybean against nematodes and insects, respectively.

Transgenic soybean overexpressing GmSAMT1 exhibits resistance to multiple-HG types of soybean cyst nematode Heterodera glycines

Summary Soybean (Glycine max (L.) Merr.) salicylic acid methyl transferase (GmSAMT1) catalyses the conversion of salicylic acid to methyl salicylate. Prior results showed that when GmSAMT1 was overexpressed in transgenic soybean hairy roots, resistance is conferred against soybean cyst nematode (SCN), Heterodera glycines Ichinohe. In this study, we produced transgenic soybean overexpressing GmSAMT1 and characterized their response to various SCN races. Transgenic plants conferred a significant reduction in the development of SCN HG type 1.2.5.7 (race 2), HG type 0 (race 3) and HG type 2.5.7 (race 5). Among transgenic lines, GmSAMT1 expression in roots was positively associated with SCN resistance. In some transgenic lines, there was a significant decrease in salicylic acid titer relative to control plants. No significant seed yield differences were observed between transgenics and control soybean plants grown in one greenhouse with 22 °C day/night temperature, whereas transgenic soybean had higher yield than controls grown a warmer greenhouse (27 °C day/23 °C night) temperature. In a 1‐year field experiment in Knoxville, TN, there was no significant difference in seed yield between the transgenic and nontransgenic soybean under conditions with negligible SCN infection. We hypothesize that GmSAMT1 expression affects salicylic acid biosynthesis, which, in turn, attenuates SCN development, without negative consequences to soybean yield or other morphological traits. Thus, we conclude that GmSAMT1 overexpression confers broad resistance to multiple SCN races, which would be potentially applicable to commercial production.

Identifying and exploring significant genomic regions associated with soybean yield, seed fatty acids, protein and oil

Soybean [Glycine max (L.) Merrill] yield and seed fatty acids, protein, and oil content are important traits for which an improved understanding of significant genomic regions would be useful. To accomplish this, a soybean population consisting of 203 F5 derived recombinant inbred lines (RILs) was developed and genotyped with 11,633 polymorphic single nucleotide polymorphisms (SNPs). Each RIL was grown in a single plot at Knoxville, TN in 2010; followed by replicated, multi-location field trials in 2013 and 2014. The data from 2010, 2013, and 2014 were analyzed together in order to detect quantitative trait loci (QTL) for these traits, and 30 total QTLs were detected. Five QTLs are candidates for confirmed status and one QTL is a candidate for positional confirmation. Many of the genes with mutations in close proximity to the fatty acid QTLs are involved in biological processes for fatty acids and/or lipids and could be considered possible candidate genes. Similarly, genes with mutations in genomic regions near yield, protein, and oil QTLs were plentiful and may contribute to the variation observed in these traits. Except for yield and stearic acid, each trait displayed pleiotropic effects with other traits in this study. Notable are the pleiotropic effects for oleic and linolenic acid on chromosomes 9, 13, and 19. Overall, the findings from this research contribute new information to the genetic understanding of soybean yield and seed fatty acids, protein and oil content. This understanding will be useful in making trait improvements.