BACKGROUND:The growing food-feed-fuel competition, declining availability of traditional feeds, higher prices, and the urgent need to provide long-term sustainability for animal production have all triggered global research into the optimum extraction of energy and nutrients from lignin-rich plant biomass. Recent studies have shown that the Pleurotus species of white rot fungus can selectively degrade lignin in lignin-rich plant biomass; however, its effectiveness in selectively degrading lignin depends on the type of substrate and species of fungus. This study was therefore designed to treat wheat straw, rice straw, and corn cob, with Pleurotus eryngii, P. ostreatus, and P. florida for 30 days under solid-state fermentation, to identify a promising fungus-substrate combination for the selective degradation of lignin and optimal improvement in the nutritional value and digestibility of each substrate. RESULTS:The type of fungus strongly influenced (P < 0.01) selectivity in lignin degradation, and the level of improvement in crude protein (CP), in vitro dry matter digestibility (IVDMD), and in vitro gas production (IVGP), in wheat straw, rice straw, and corn cob. Fungus-substrate interaction data revealed that P. ostreatus caused maximum (P < 0.05) degradation of lignin, and greater (P < 0.05) improvement in CP, IVDMD, and IVGP in wheat straw and rice straw. The lowest (P < 0.05) degradation of lignin and improvement in CP, IVDMD, and IVGP was caused by P. eryngii in corn cob. Among the fungi, the maximum (P < 0.05) degradation of lignin, and greater (P < 0.05) improvement in CP, IVDMD, and IVGP were caused by P. florida as compared with those of P. ostreatus and P. eryngii. CONCLUSION:The results highlight significant influence of fungus-substrate combination for selective lignin degradability and the consequent improvement in the nutritional value of the substrates. Maximum selective lignin degradability and improvement in nutritional value and digestibility was caused by P. ostreatus in wheat straw and in rice straw, and by P. florida in corn cob.

Soybean is a major source of protein and is the second largest source of oil worldwide. Developing soybean lines with high levels of stearic acid is a primary goal of the soybean industry. Unlike other polyunsaturated fatty acids, the saturated stearic acid is desirable for nutrition because it does not exhibit cholesterolemic effects on human health. Most developed high stearic acid soybeans carry different GmSACPD-C mutated alleles. However, due to its dual role in both seeds and nodule development, all derived deleterious GmSACPD-C mutant alleles are of extremely poor agronomic value as a result of defective nodulation. The soybean Stearoyl-acyl carrier protein desaturase (GmSACPD) gene family is composed of five members. Comparative genomics analysis indicated that SACPD genes were duplicated and derived from a common ancestor that is still present in chlorophytic algae. Synteny analysis shows the presence of segment duplications between GmSACPD-A/GmSACPD-B, and GmSACPD-C/GmSACPD-D. However, GmSACPD-E was not contained in any duplicated segment and may be the result of tandem duplication. In the present study, we developed a TILLING by Target Capture Sequencing (Tilling-by-Sequencing +) technology, a versatile extension of the conventional TILLING by sequencing, and successfully identified 12, 14, and 18 EMS mutants at the GmSACPD-A, GmSACPD-B, and GmSACPD-D genes, respectively. Functional analysis of all identified mutants reveals an unprecedented role of the three GmSACPD-A, GmSACPD-B, and GmSACPD-D members in unsaturated fatty acid biosynthesis without affecting nodule development and structure. This new discovery will positively impact the development of high stearic acid lines to enhance soybean nutritional value without potential developmental tradeoffs

No abstract

Soybean is the second largest source of oil worldwide. Developing soybean varieties with high levels of oleic acid is a primary goal of the soybean breeders and industry. Edible oils containing high level of oleic acid and low level of linoleic acid are considered with higher oxidative stability and can be used as a natural antioxidant in food stability. All developed high oleic acid soybeans carry two alleles; GmFAD2-1A and GmFAD2-1B. However, when planted in cold soil, a possible reduction in seed germination was reported when high seed oleic acid derived from GmFAD2-1 alleles were used. Besides the soybean fatty acid desaturase (GmFAD2-1) subfamily, the GmFAD2-2 subfamily is composed of five members, including GmFAD2-2A, GmFAD2-2B, GmFAD2-2C, GmFAD2-2D, and GmFAD2-2E. Segmental duplication of GmFAD2-1A/GmFAD2-1B, GmFAD2-2A/GmFAD2-2C, GmFAD2-2A/GmFAD2-2D, and GmFAD2-2D/GmFAD2-2C have occurred about 10.65, 27.04, 100.81, and 106.55 Mya, respectively. Using TILLING-by-Sequencing+ technology, we successfully identified 12, 8, 10, 9, and 19 EMS mutants at the GmFAD2-2A, GmFAD2-2B, GmFAD2-2C, GmFAD2-2D, and GmFAD2-2E genes, respectively. Functional analyses of newly identified mutants revealed unprecedented role of the five GmFAD2-2A, GmFAD2-2B, GmFAD2-2C, GmFAD2-2D, and GmFAD2-2E members in controlling the seed oleic acid content. Most importantly, unlike GmFAD2-1 members, subcellular localization revealed that members of the GmFAD2-2 subfamily showed a cytoplasmic localization, which may suggest the presence of an alternative fatty acid desaturase pathway in soybean for converting oleic acid content without substantially altering the traditional plastidial/ER fatty acid production.