Development of soybean [Glycine max (L.) Merr.] varieties with high seed protein concentration are hindered by a negative correlation between seed protein and yield. "Benning HP," a genotype that breaks this tradeoff, contains an introgressed high-protein allele. Field and growth chamber experiments were conducted to identify N flux(es) that enable Benning HP's increased seed protein without a yield penalty. When the N source was completely controlled, Benning HP could fix more N than its recurrent parent, but this depended on the rhizobium strain and plant developmental stage. In the field, Benning HP remobilized N from its leaves at a higher rate than its recurrent parent during seed fill in only one of the years studied. These results demonstrate that Benning HP has higher potential N fixation and N remobilization from vegetative tissue compared to its lower protein parent, but the expression of those traits may depend on environment and sink control.

Identification and characterization of a 254-kb genomic deletion on a duplicated chromosome segment that resulted in a low level of palmitic acid in soybean seeds using transcriptome sequencing. A large number of soybean genotypes varying in seed oil composition and content have been identified. Understanding the molecular mechanisms underlying these variations is important for breeders to effectively utilize them as a genetic resource. Through design and application of a bioinformatics approach, we identified nine co-regulated gene clusters by comparing seed transcriptomes of nine soybean genotypes varying in oil composition and content. We demonstrated that four gene clusters in the genotypes M23, Jack and N0304-303-3 coincided with large-scale genome rearrangements. The co-regulated gene clusters in M23 and Jack mapped to a previously described 164-kb deletion and a copy number amplification of the Rhg1 locus, respectively. The coordinately down-regulated gene clusters in N0304-303-3 were caused by a 254-kb deletion containing 19 genes including a fatty acyl-ACP thioesterase B gene (FATB1a). This deletion was associated with reduced palmitic acid content in seeds and was the molecular cause of a previously reported nonfunctional FATB1a allele, fap nc . The M23 and N0304-304-3 deletions were located in duplicated genome segments retained from the Glycine-specific whole genome duplication that occurred 13 million years ago. The homoeologous genes in these duplicated regions shared a strong similarity in both their encoded protein sequences and transcript accumulation levels, suggesting that they may have conserved and important functions in seeds. The functional conservation of homoeologous genes may result in genetic redundancy and gene dosage effects for their associated seed traits, explaining why the large deletion did not cause lethal effects or completely eliminate palmitic acid in N0304-303-3.

fap 1 mutation is caused by a G174A change in GmKASIIIA that disrupts a donor splice site recognition and creates a GATCTG motif that enhanced its expression.

Soybean [Glycine max (L.) Merr] plants were exposed to three temperature regimens during seed development to investigate the effect of temperature on the expression of eight defense-related genes and the accumulation of two fungal pathogens in inoculated seeds. In seeds prior to inoculation, either a day/night warm (34/26°C) or a cool temperature (22/18°C) relative to normal (26/22°C) resulted in altered patterns of gene expression including substantially lower expression of PR1, PR3 and PR10. After seed inoculation with Cercospora kikuchii, pathogen accumulation was lowest in seeds produced at 22/18°C in which of all defense genes, MMP2 was uniquely most highly induced. For seeds inoculated with Diaporthe phaseolorum, pathogen accumulation was lowest in seeds produced at 34/26°C in which of all defense genes, PR10 was uniquely most highly induced. Our detached seed assays clearly demonstrated that the temperature regimens we applied during seed development produced significant changes in seed defense-related gene expression both pre- and post inoculation and our findings support the hypothesis that global climate change may alter plant–pathogen interactions and thereby potentially crop productivity.

ABSTRACTWe characterized soybean [Glycine max (L.) Merr.] FAD7 and FAD8 gene structure and expression responses to temperature and pathogen stress to compare and contrast these features to those reported for higher plant plastidal omega‐3 (ω‐3) desaturases. We found that the genomic structure and deduced amino acid sequence of soybean FAD7 and FAD8 are similar to other higher plant plastidal ω‐3 desaturases: eight exons and seven introns, predicted proteins of 453 amino acid residues containing three conserved histidine motifs, amino terminal chloroplast transit peptides, and molecular masses of 51.3 and 51.4 kDa, respectively. GmFAD7 has 76% amino acid sequence identity to GmFAD8. Two complete copies of GmFAD7, one on chromosome 18 and one on chromosome 7, and two complete copies of GmFAD8, one on chromosome 3 and one on chromosome 1 of the ‘Williams 82’ soybean genome, were found with strong sequence similarity to GmFAD7 and GmFAD8 of cultivar Dare. Dare GmFAD7 transcript expression in leaves remained at a relatively low level and was unaffected by any of the temperature treatments we imposed, but GmFAD8 transcript accumulation was sharply upregulated by a cool temperature (20/16°C day/night) after a 12 h exposure and total linolenic acid as a percent of total leaf fatty acids increased from 60 to about 68% after 48 h at the cool temperature. Inoculation of soybean leaves with the fungal pathogen Cercospora kikuchii differentially upregulated the level of GmFAD7 transcripts to twice that of GmFAD8 by 12 h postinoculation. The response of soybean foliar FAD8 expression and linolenic acid levels to cool temperature was similar to observations in other plants. On the other hand, despite increased soybean FAD7 expression in response to foliar pathogen stress the expected associated increase in foliar linolenic acid was not detected.

Seeds of the mid-oleic acid soybean mutant M23 accumulate higher levels of oleic acid (50–60% oleate) by virtue of a deletion of GmFAD2-1A, an allele of the microsomal omega-6 oleate desaturase gene. In other less well characterized soybean varieties that are phenotypically mid-oleic, little is known about the expression levels of omega-6 desaturase GmFAD2 genes and other candidate genes that determine seed oleic acid content. We compared the steady-state transcript abundance during seed development of the oleate-ACP thioesterase (GmFATB1a), delta-9 stearoyl acyl carrier protein desaturase (GmSACPD) and the omega-6 fatty acid desaturase (GmFAD2) genes in five natural mid-oleic varieties and mutant M23 to gene expression data for the conventional non mid-oleic cultivar Dare. We found that, relative to Dare, there were instances where lower expression of GmFATB1a, GmFAD2-1A, GmFAD2-1B, GmFAD2-2, and GmFAD2-3 and higher expression of the GmSACPD-C might be associated with the mid-oleic seed phenotype. This finding suggests that of the several soybean genomic loci known or suspected to be involved in oleic acid phenotype, some are likely to encode genes involved in regulation of transcription of the oleate biosynthetic genes.

Soybean leaves and detached seeds were inoculated with either Cercospora kikuchii or Diaporthe phaseolorum var. meridionalis in order to characterize the defense responses of these tissues to fungal infection. By comparing and contrasting the expression of 15 soybean defense-related genes in the two tissues during a 48 h post infection period, we found that pathogen concentrations and gene expression patterns were substantially different for inoculated leaves and seeds of the susceptible cultivar Holladay, but for each tissue a generally similar pattern of expression was observed with either pathogen treatment. In leaves inoculated with C. kikuchii or D. phaseolorum, 14/15 or 8/15 defense-related genes were significantly upregulated, respectively, including the notably strong upregulation of PR3 (chitinase 1) and PR10 (ribonuclease-like protein) by both pathogens. In leaves, the pathogen concentrations declined during the 48 hpi period. In seeds inoculated with either C. kikuchii or D. phaseolorum, 7/15 or 6/15 genes were significantly upregulated, but PR3 and PPO (polyphenol oxidase) were not significantly upregulated or not detected with either pathogen treatment, while PR10 was significantly upregulated only in seeds inoculated with D. phaseolorum. Pathogen concentrations in seeds did not decline, but increased over the 48 hpi period. Our results suggest that differences between the numbers and types of defense genes upregulated in the two inoculated tissues may explain, at least partially, the decline in leaves and the increase in seeds of the pathogen quantities. Published by Elsevier Ltd.