Variability in soybean yield responses to elevated atmospheric CO2: Insights from non-structural carbohydrate remobilisation during seed filling.

The increasing atmospheric CO2 concentration (e[CO2]) has mixed effects on soybean most varieties' yield. This study elucidated the effect of e[CO2] on soybean yield and the underlying mechanisms related to photosynthetic capacity, non-structural carbohydrate (NSC) accumulation, and remobilisation. Four soybean cultivars were cultivated in open-top chambers at two CO2 levels. Photosynthesis rates were determined from R2 to R6. Plants were sampled at R5 and R8 to determine carbohydrate concentrations. There were significant variations in yield responses among the soybean cultivars under e[CO2], from no change in DS1 to a 22% increase in SN14. DS1 and SN14 had the smallest and largest increase, respectively, in daily carbon assimilation capacity. Under e[CO2], DS1, MF5, and XHJ had an increase in Ci, at which point the transition from Rubisco-limited to ribulose-1,5-bisphosphate regeneration-limited photosynthesis occurred, in contrast with SN14. Thus, the cultivars might have distinct mechanisms that enhance photosynthesis under e[CO2] conditions. A positive correlation was between daily carbon assimilation response to e[CO2] and soybean yield, emphasising the importance of enhanced photosynthate accumulation before the R5 stage in determining yield response to e[CO2]. E[CO2] significantly influenced NSC accumulation in vegetative organs at R5, with variation among cultivars. There was enhanced NSC remobilisation during seed filling, indicating cultivar-specific responses to the remobilisation of sucrose and soluble sugars, excluding sucrose and starch. A positive correlation was between leaf and stem NSC remobilisation and yield response to e[CO2], emphasising the role of genetic differences in carbohydrate remobilisation mechanisms in determining soybean yield variation under elevated CO2 levels.

Developmental dynamic transcriptome and systematic analysis reveal the major genes underlying isoflavone accumulation in soybean.

Introduction: Soy isoflavone, a class of polyphenolic compounds exclusively occurred in legumes, is an important bioactive compound for both plants and human beings. The outline of isoflavones biosynthesis pathway has been drawn up basically in the previous research. However, research on the subject has been mostly restricted to investigate the static regulation of isoflavone content in soybean, rather than characterize its dynamic variation and modulation network in developing seeds. Methods: In this study, by using eight recombinant inbred lines (RIL), the contents of six isoflavone components in the different stages of developing soybean seeds were determined to characterize the dynamic variation of isoflavones, and the isoflavones accumulation pattern at physiological level was investigated. Meanwhile, we integrated and analyzed the whole genome expression profile of four lines and 42 meta-transcriptome data, based on the multiple algorithms. Results: This study: 1) obtained 4 molecular modules strongly correlated with isoflavone accumulation; 2) identified 28 novel major genes that could affect the accumulation of isoflavones in developing seeds free from the limitation of environments; 3) discussed the dynamic molecular patterns regulating isoflavones accumulation in developing seed; 4) expanded the isoflavone biosynthesis pathway. Discussion: The results not only promote the understandings on the biosynthesis and regulation of isoflavones at physiological and molecular level, but also facilitate to breed elite soybean cultivars with high isoflavone contents.

Irradiation with carbon ion beams affects soybean nutritional quality in early generations.

As people's demand for healthy diet increases, improving soybean seed nutritional quality is becoming as important as yield. Carbon ion beam radiation (CIBR) is an effective method to create soybean mutants, and thus breeding cultivars with better seed nutritional quality. In this study, the high-yield soybean line 'Dongsheng 28' was used, and three CIBR doses (100, 120, and 140 Gy) were used to explore the characteristics of quality separation and variation in the offspring of early mutant populations. Eleven quality traits, including protein, oil, sucrose, soluble sugar, iron (Fe), manganese (Mn), zinc (Zn), cupper (Cu), daidzin, glycitin, and genistin concentrations were analyzed in the M2 and M3 generations. The results revealed that the range of protein and oil concentration of all three CIBR doses changed by 38.5-42.9% and 18.8-23.8% in the M2 and M3 generations, respectively, while soluble sugar and sucrose concentrations changed by 48.1-123.4 and 22.7-74.7 mg/g, with significant effects by 140 Gy across the two generations. Therefore, around the optimum range, a higher CIBR dose is better for high protein, oil, and sugar varieties selection. In general, irradiation raised isoflavone concentrations, but 140 Gy had an inhibitory effect on isoflavone concentrations in the M3 generation. Although a variety could not be released in the M2 or M3 generation, the results of this study have important guiding significance for the targeted cultivation of specific nutritional quality materials. For instance, a lower irradiation dose is preferable when breeding targets are higher isoflavones and Mn concentrations. It is essential to increase the irradiation dose if the breeding targets contain high levels of protein, oil, sucrose, soluble sugars, Fe, Zn, and Cu.

Novel QTL and Meta-QTL Mapping for Major Quality Traits in Soybean.

Isoflavone, protein, and oil are the most important quality traits in soybean. Since these phenotypes are typically quantitative traits, quantitative trait locus (QTL) mapping has been an efficient way to clarify their complex and unclear genetic background. However, the low-density genetic map and the absence of QTL integration limited the accurate and efficient QTL mapping in previous researches. This paper adopted a recombinant inbred lines (RIL) population derived from 'Zhongdou27'and 'Hefeng25' and a high-density linkage map based on whole-genome resequencing to map novel QTL and used meta-analysis methods to integrate the stable and consentaneous QTL. The candidate genes were obtained from gene functional annotation and expression analysis based on the public database. A total of 41 QTL with a high logarithm of odd (LOD) scores were identified through composite interval mapping (CIM), including 38 novel QTL and 2 Stable QTL. A total of 660 candidate genes were predicted according to the results of the gene annotation and public transcriptome data. A total of 212 meta-QTL containing 122 stable and consentaneous QTL were mapped based on 1,034 QTL collected from previous studies. For the first time, 70 meta-QTL associated with isoflavones were mapped in this study. Meanwhile, 69 and 73 meta-QTL, respectively, related to oil and protein were obtained as well. The results promote the understanding of the biosynthesis and regulation of isoflavones, protein, and oil at molecular levels, and facilitate the construction of molecular modular for great quality traits in soybean.

Root K Affinity Drivers and Photosynthetic Characteristics in Response to Low Potassium Stress in K High-Efficiency Vegetable Soybean.

Significant variations of potassium absorption and utilization exist in vegetable soybean. Pot and hydroponic experiments were carried out to examine the characteristics of root potassium (K) affinity-associated drivers and photosynthesis in vegetable soybean (edamame) [Glycine max (L.) Merr.] with different K efficiency. Two K high-efficiency vegetable soybean genotypes (Line 19 and Line 20) and two K low-efficiency genotypes (Line 7 and Line 36) were investigated in low K and normal K conditions. The root of K high-efficiency genotypes had a higher K+ affinity associated with a higher maximum K+ uptake rate (Imax), but lower Michaelis constant for K+ absorption (Km) and lower compensation concentration for K+ uptake (Cmin). Seedlings of K high-efficiency genotypes also had higher root vigor [triphenyl tetrazolium chloride (TTC) reduction method] and greater absorbing activity (methylene blue method), especially in the low K condition. Furthermore, the root bleeding-sap rate of K high-efficiency genotypes in low K stress was 9.9-24.3% greater than that of normal K conditions, which was accompanied by a relatively higher K concentration of root bleeding-sap in contributing to K+ upward flux. The root of K high-efficiency vegetable soybean genotypes exhibited K+ high-affinity and driving advantages. Photosynthetic parameters of K high-efficiency vegetable soybean genotypes were less affected by low K stress. Low K stress decreased the net photosynthetic rate of K high-efficiency genotypes by 6.1-6.9%, while that of K low-efficiency genotypes decreased by 10.9-15.7%. The higher chlorophyll (Chl) a/b ratio with enhanced relative content of Chl a in response to low K stress might be an adapted mechanism for K high-efficiency genotypes to maintain photosynthetic capacity. Stronger root K affinity drivers associated with photosynthetic adaptability to low K stress are the key factors in determining the K high-efficiency of vegetable soybeans.

Distinct effects of short-term reconstructed topsoil on soya bean and corn rhizosphere bacterial abundance and communities in Chinese Mollisol.

Eroded black soils (classified as Mollisols) lead to a thinner topsoil layer, reduced organic carbon storage and declined crop productivity. Understanding the changes in soil microbial communities owing to soil erosion is of vital importance as soil microbial communities are sensitive indicators of soil condition and are essential in soil nutrient cycling. This study used the reconstructed facility with 10, 20 and 30 cm topsoil thickness under no-till soya bean-corn rotation in black soil region of Northeast China. Illumina MiSeq sequencing targeting 16S rRNA, qPCR and soil respiration measurement were performed to assess the changes in soya bean and corn rhizosphere bacterial communities, as well as their abundance and activities due to the topsoil thickness. The results showed that soil bacterial communities from both soya bean and corn were more sensitive to topsoil removal than to soil biogeochemical characteristics. Topsoil depths significantly influenced both soya bean and corn bacterial communities, while they only significantly influenced the bacterial abundance and respiration in corn. We also found that the topsoil depths significantly induced the changes in phyla and genera from both soya bean and corn rhizosphere bacterial community, which aid further understandings on how topsoil layer influences the global nutrient cycling of Mollisols by influencing the change in microbial communities.

Impact of Elevated CO2 on Seed Quality of Soybean at the Fresh Edible and Mature Stages.

Although the effect of elevated CO2 (eCO2) on soybean yield has been well documented, few studies have addressed seed quality, particularly at the fresh edible (R6) and mature stages (R8). Under the current global scenario of increasing CO2 levels, this potentially threatens the nutritional content and quality of food crops. Using four soybean cultivars, we assessed the effects of eCO2 on the concentrations of crude protein, crude oil, and isoflavones and analyzed the changes in free amino acids, fatty acids, and mineral elements in seeds. At R6, eCO2 had no influence on soybean seed protein and oil concentrations. At R8, eCO2 significantly decreased seed protein concentration but increased seed oil concentration; it also significantly decreased total free amino acid concentration. However, at the same stage, the proportion of oleic acid (18:1) among fatty acids increased in response to eCO2 in the cultivars of Zhongke-maodou 2 (ZK-2) and Zhongke-maodou 3 (ZK-3), and a similar trend was found for linoleic acid (18:2) in Zhongke-maodou 1 (ZK-1) and Hei-maodou (HD). Total isoflavone concentrations increased significantly at both the R6 and R8 stages in response to eCO2. Compared with ambient CO2, the concentrations of K, Ca, Mg, P, and S increased significantly under eCO2 at R6, while the Fe concentration decreased significantly. The response of Zn and Mn concentrations to eCO2 varied among cultivars. At R8 and under eCO2, Mg, S, and Ca concentrations increased significantly, while Zn and Fe concentrations decreased significantly. These findings suggest that eCO2 is likely to benefit from the accumulation of seed fat and isoflavone but not from that of protein. In this study, the response of seed mineral nutrients to eCO2 varied between cultivars.

Reduced abscisic acid content is responsible for enhanced sucrose accumulation by potassium nutrition in vegetable soybean seeds.

In order to understand the physiological mechanism of potassium (K) application in enhancing sugar content of vegetable soybean seeds, pot experiments were conducted in 2014 and 2015 with two vegetable soybean (Glycine max L. Merr.) cultivars (c.v. Zhongkemaodou 1 and c.v. 121) under normal rate of nitrogen and phosphorus application. Three potassium (K) fertilization treatments were imposed: No K application (K0), 120 kg K2SO4 ha-1 at seeding (K1), and 120 kg K2SO4 ha-1 at seedling + 1% K2SO4 foliar application at flowering (K2). Contents of indole-3-acetic acid (IAA), gibberellins (GA), cytokinins (ZR) and abscisic acid (ABA) in seeds were determined from 4 to 8 weeks after flowering. K fertilization increased the contents of IAA, GA, ZR, soluble sugar, sucrose and fresh pod yield, but reduced ABA content consistently. When the contents of soluble sugar and sucrose reached the highest level at 7 weeks after flowering for the 2 cultivars, the contents of IAA、GA、ZR all reached the lowest level in general. The content of ABA in seed was negatively correlated with the sucrose content (P < 0.01, r = -0.749**, -0.768** in 2014 and -0.535**, -0.791** in 2015 for c.v.121 and c.v. Zhongkemaodou 1 respectively). The changes in ratio of the ABA to (IAA + GA + ZR) from 4 to 8 weeks after flowering affected by K application were coincident to the changes of sucrose accumulation. The reduced ratio of ABA/(IAA + GA + ZR) affected by K nutrition particularly reduced abscisic acid content plays a critical role in enhancing sucrose content, which might be a partial mechanism involved in K nutrition to improve the quality of vegetable soybean.