1987). In the low seed linolenic acid line A5 (Fehr et al., 1992), the fan(A5) locus was shown to be associated Three independent genetic loci have been shown to contribute to with a deletion in an undefined omega-3 fatty-acid desoybean [Glycine max (L.) Merrill] seed linolenic acid levels, including the well-characterized Fan locus. Linolenic acid is the product of saturase gene (Byrum et al., 1997). Omega-3 fatty-acid omega-3 fatty-acid desaturase enzyme activity. The objective of this desaturases catalyze a third double bond into linoleic study was to identify and characterize the family of soybean omega-3 acid precursors to produce linolenic acid. Both chlorofatty-acid desaturase genes and link them to low seed linolenic acid plast-targeted and microsomal omega-3 fatty-acid desatas a tool for the development of molecular markers for low linolenic urases have been identified in plants, but the microsomal acid soybean. Using database homology searches and gene cloning, enzymes have been shown to be the major contributors we identified and characterized three soybean microsomal omega-3to seed linolenic acid levels (Yadav et al., 1993). fatty-acid desaturase genes that contribute to seed linolenic acid levels.The model plant Arabidopsis thaliana (L.) Heynh. Relative expression was characterized by quantitative real-time RT-contains one gene encoding a microsomal omega-3 PCR (reverse transcriptase-polymerase chain reaction). One of the fatty-acid desaturase (FAD3) and two chloroplast tarthree genes was predominantly expressed in developing seeds. We determined that the low linolenic acid breeding line A5 (fan fan) geted enzymes (FAD7 and FAD8). Mutation of FAD3 contains two of the genes, but is missing the third sequence. Therefore, in Arabidopsis reduced seed linolenic acid levels to 3%

three fatty acid desaturase gene FAD3 (Bilyeu et al., 2003). GmFAD3A was also characterized as the most One major locus (Fan) and several minor loci have been shown highly expressed of the three homologs in developing to contribute to the linolenic acid level in soybean [Glycine max (L.) Merr.] seeds. The Fan gene encodes a microsomal omega-3 fatty acid seeds. The relative importance of GmFAD3B and desaturase (Arabidopsis FAD3 homolog), and soybeans contain three GmFAD3C to seed linolenic acid levels has not yet FAD3 genes. The objective of this work was to characterize candidate been described, although they have been shown to be soybean FAD3 genes from low linolenic acid soybean lines and associexpressed at low levels in developing seeds (Bilyeu et ate those alleles with the trait. Mutations in two of the three soybean al., 2003). Nuclear-encoded, chloroplast-targeted omega-FAD3 genes were identified, and genotypes with the mutant alleles three fatty acid desaturases may also contribute to seed conferred a reduction of over two thirds of the linolenic acid present linolenic acid levels (Yadav et al., 1993). Omega-3 fatty in the seed. The two mutant genes contributed unequally but additively to the phenotype. The results demonstrated that the mutant genotype

Forage legumes benefit pastures and hay crops by fixing N, improving seasonal distribution of growth, and enhancing animal performance, but their lack of persistence is viewed as a major limitation. Stand persistence depends largely on plant persistence in crown‐forming perennials that do not spread by stolons or rhizomes, but depends on seed production, timely germination, and seedling survival in annuals, biennials, and many short‐lived perennials. Stolon‐ and rhizome‐forming perennials can colonize unoccupied areas if management is favorable. Conversely, differentials in seed production, seed dispersal mechanisms, and seed survival allow reseeding annuals, biennials, and short‐lived perennials to colonize areas that are more widely dispersed. Several pathogens and insects invade the stand each year, but to different intensities depending on climatic and crop management conditions. Other pathogens and insects reside in production fields and pastures, gradually increasing in population while reducing plant persistence, the seed bank, and seedling survival. Environmental and management stresses weaken plants, which are subsequently killed by combined influences of environmental stresses, resident insects, and pathogens. Improving disease and insect resistance is a major breeding objective for crown formers, but these efforts have to be supplemented by physiological improvement in stress resistance. To improve stand persistence of annuals, management and genetic information is needed on seed production capacity, hard seed content, seed bank management, and optimizing conditions for seed germination and seedling survival. The long‐term goal is to improve cultivar persistence, and develop management systems to aid legume persistence in a wide range of grassland ecosystems. Educational programs are also essential. Research Question Most producers understand the importance of legumes in forage systems, but management decisions that enhance short‐term yields or quality of a grass‐legume association can reduce persistence of the legume component. Our objective was to review the biology of legume persistence and evaluate management strategies associated with enhanced plant persistence of crown‐forming perennial legumes and reseeding properties of annual legumes and short‐lived perennials. Interactions of legumes with biological pests, environmental stresses, and associated grasses were considered. Literature Summary Legumes enhance animal performance and reduce N needs for grass pastures, but legumes seldom dominate in agricultural or natural ecosystems. Thus, the association must be managed to enhance vigor and persistence of the legume. Legume breeders have emphasized temperature resistance, especially cold adaptation, and disease resistance for crown‐forming perennials like alfalfa, but enhanced disease resistance and improved productivity may be at the expense of winterhardiness. Conversely, annual legumes are generally improved by increasing seed production and seedling vigor. The role of hard seed and dynamics of t...

The effects of high temperature treatment on soybean [Glycine max (L.) Merr.] seed composition, vigor, and proteome were investigated using mature dry seeds harvested from plants grown in environment‐controlled chambers. High day/night temperatures (37/30°C) from stages R5 through R8 altered ratios of individual fatty acids to total fatty acid compared to the control (27/18°C). Concentration of sugars decreased, but total protein and phytic acid concentration were unchanged. High temperature resulted in a greater proportion of abnormal seeds, but normal‐appearing seed exhibited reduced germination and vigor. Proteomic analysis detected 20 protein identities whose accumulations were changed by the high temperature. Fourteen spots were identified as seven subunits of seed storage proteins. The remaining six proteins were identified as those responding to abiotic stresses or having a function in respiration: (i) sucrose binding protein, (ii) Class III acidic endochitinase, (iii) heat shock protein (HSP22), (iv) late embryo abundant protein, (v) Bowman–Birk proteinase inhibitor, and (vi) formate dehydrogenase. High temperature during seed development changed soybean seed composition and decreased seed vigor, but also changed seed protein expression profiles.

Phytic acid (PA) contains the major portion of the phosphorus in the soybean (Glycine max) seed and chelates divalent cations. During germination, both minerals and phosphate are released upon phytase-catalyzed degradation of PA. We generated a soybean line (CAPPA) in which an Escherichia coli periplasmic phytase, the product of the appA gene, was expressed in the cytoplasm of developing cotyledons. CAPPA exhibited high levels of phytase expression, $90% reduction in seed PA, and concomitant increases in total free phosphate. These traits were stable, and, although resulted in a trend for reduced emergence and a statistically significant reduction in germination rates, had no effect on the number of seeds per plant or seed weight. Because phytate is not digested by monogastric animals, untreated soymeal does not provide monogastrics with sufficient phosphorus and minerals, and PA in the waste stream leads to phosphorus runoff. The expression of a cytoplasmic phytase in the CAPPA line therefore improves phosphorus availability and surpasses gains achieved by other reported transgenic and mutational strategies by combining in seeds both high phytase expression and significant increases in available phosphorus. Thus, in addition to its value as a high-phosphate meal source, soymeal from CAPPA could be used to convert PA of admixed meals, such as cornmeal, directly to utilizable inorganic phosphorus.