Transcriptomic investigation unveils the role of energy metabolism under low phosphorus and salt combined stress in soybean (Glycine max).

Soybean (Glycine max) is economically significant, but the mechanisms underlying its adaptation to simultaneous low phosphorus and salt stresses are unclear. We employed the Shennong 94-1-8 soybean germplasm to conduct a comprehensive analysis, integrating both physiochemical and transcriptomic approaches, to unravel the response mechanisms of soybean when subjected to simultaneous low phosphorus and salt stresses. Remarkably, the combined stress exhibited the most pronounced impact on the soybean root system, which led to a substantial reduction in total soluble sugar (TSS) and total soluble protein (TSP) within the plants under this treatment. A total of 20,953 differentially expressed genes were identified through pairwise comparisons. Heatmap analysis of genes related to energy metabolism pathways demonstrated a significant down-regulation in expression under salt and low phosphorus + salt treatments, while low phosphorus treatment did not exhibit similar expression trends. Furthermore, the weighted gene co-expression network analysis (WGCNA) indicated that the blue module had a strong positive correlation with TSS and TSP. Notably, 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase 1, FCS-Like Zinc finger 8, auxin response factor 18 isoform X2, and NADP-dependent malic enzyme emerged as hub genes associated with energy metabolism. In summary, our findings indicate that soybean roots are more adversely affected by salt and combined stress than by low phosphorus alone due to reduced activity in energy metabolism-related pathways and hub genes. These results offer novel insights into the adaptive mechanisms of soybeans when facing the combined stress of low phosphorus and salinity.

Comparative physiological and transcriptomic analysis of two salt-tolerant soybean germplasms response to low phosphorus stress: role of phosphorus uptake and antioxidant capacity.

BACKGROUND: Phosphorus (P) and salt stress are common abiotic stressors that limit crop growth and development, but the response mechanism of soybean to low phosphorus (LP) and salt (S) combined stress remains unclear. RESULTS: In this study, two soybean germplasms with similar salt tolerance but contrasting P-efficiency, A74 (salt-tolerant and P-efficient) and A6 (salt-tolerant and P-inefficient), were selected as materials. By combining physiochemical and transcriptional analysis, we aimed to elucidate the mechanism by which soybean maintains high P-efficiency under salt stress. In total, 14,075 differentially expressed genes were identified through pairwise comparison. PageMan analysis subsequently revealed several significantly enriched categories in the LP vs. control (CK) or low phosphorus + salt (LPS) vs. S comparative combination when compared to A6, in the case of A74. These categories included genes involved in mitochondrial electron transport, secondary metabolism, stress, misc, transcription factors and transport. Additionally, weighted correlation network analysis identified two modules that were highly correlated with acid phosphatase and antioxidant enzyme activity. Citrate synthase gene (CS), acyl-coenzyme A oxidase4 gene (ACX), cytokinin dehydrogenase 7 gene (CKXs), and two-component response regulator ARR2 gene (ARR2) were identified as the most central hub genes in these two modules. CONCLUSION: In summary, we have pinpointed the gene categories responsible for the LP response variations between the two salt-tolerant germplasms, which are mainly related to antioxidant, and P uptake process. Further, the discovery of the hub genes layed the foundation for further exploration of the molecular mechanism of salt-tolerant and P-efficient in soybean.

Identification and validation of major QTLs associated with low seed coat deficiency of natto soybean seeds (Glycine max L.).

KEY MESSAGE: Two major QTLs associated with low seed coat deficiency of soybean seeds were identified in two biparental populations, and three SNP markers were validated to assist low-SCD natto soybean breeding selection. Soybean seed coat deficiency (SCD), known as seed coat cracking during soaking in the natto production process, is problematic because split or broken beans clog production lines and increases production costs. Development of natto soybean cultivars with low SCD is crucial to support the growth of the natto industry. Unfortunately, information on the genetic control of SCD in soybean, which is desperately needed to facilitate breeding selection, remains sparse. In this study, two F2 populations derived from V11-0883 × V12-1626 (Pop 1) and V11-0883 × V12-1885 (Pop 2) were developed and genotyped with BARCSoySNP6K Beadchips and F2-derived lines were evaluated for SCD in three consecutive years (2016-2018) in order to identify quantitative trait loci (QTLs) associated with low SCD in soybean. A total of 17 QTLs underlying SCD were identified in two populations. Among these, two major and stable QTLs, qSCD15 on chromosome 15 and qSCD20 on chromosome 20, were detected across multiple years. These QTLs explained up to 30.3% of the phenotypic variation for SCD in Pop 1 and 6.1% in Pop 2 across years. Three SNP markers associated with the qSCD20 were validated in additional four biparental populations. The average selection efficiency of low-SCD soybean was 77% based on two tightly linked markers, Gm20_34626867 and Gm20_34942502, and 64% based on the marker Gm20_35625615. The novel and stable QTLs identified in this study will facilitate elucidation of the genetic mechanism controlling SCD in soybean, and the markers will significantly accelerate breeding for low-SCD soybean through marker-assisted selection.

Genome-wide association mapping for seed protein and oil contents using a large panel of soybean accessions.

Soybean is globally cultivated primarily for its protein and oil. The protein and oil contents of the seeds are quantitatively inherited traits determined by the interaction of numerous genes. In order to gain a better understanding of the molecular foundation of soybean protein and oil content for the marker-assisted selection (MAS) of high quality traits, a population of 185 soybean germplasms was evaluated to identify the quantitative trait loci (QTLs) associated with the seed protein and oil contents. Using specific length amplified fragment sequencing (SLAF-seq) technology, a total of 12,072 single nucleotide polymorphisms (SNPs) with a minor allele frequency (MAF) ≥ 0.05 were detected across the 20 chromosomes (Chr), with a marker density of 78.7 kbp. A total of 31 SNPs located on 12 of the 20 soybean chromosomes were correlated with seed protein and oil content. Of the 31 SNPs that were associated with the two target traits, 31 beneficial alleles were identified. Two SNP markers, namely rs15774585 and rs15783346 on Chr 07, were determined to be related to seed oil content both in 2015 and 2016. Three SNP markers, rs53140888 on Chr 01, rs19485676 on Chr 13, and rs24787338 on Chr 20 were correlated with seed protein content both in 2015 and 2016. These beneficial alleles may potentially contribute towards the MAS of favorable soybean protein and oil characteristics.

Effect of Drought Stress during Soybean R2-R6 Growth Stages on Sucrose Metabolism in Leaf and Seed.

Sucrose is the main photosynthesis product of plants and the fundamental carbon skeleton monomer and energy supply for seed formation and development. Drought stress induces decreased photosynthetic carbon assimilation capacity, and seriously affects seed weight in soybean. However, little is known about the relationship between decreases in soybean seed yield and disruption of sucrose metabolism and transport balance in leaves and seeds during the reproductive stages of crop growth. Three soybean cultivars with similar growth periods, "Shennong17", "Shennong8", and "Shennong12", were subjected to drought stress during reproductive growth for 45 days. Drought stress significantly reduced leaf photosynthetic rate, shoot biomass, and seed weight by 63.93, 33.53, and 41.65%, respectively. Drought stress increased soluble sugar contents, the activities of sucrose phosphate synthase, sucrose synthase, and acid invertase enzymes, and up-regulated the expression levels of GmSPS1, GmSuSy2, and GmA-INV, but decreased starch content by 15.13% in leaves. Drought stress decreased the contents of starch, fructose, and glucose in seeds during the late seed filling stages, while it induced sucrose accumulation, which resulted in a decreased hexose-to-sucrose ratio. In developing seeds, the activities of sucrose synthesis and degradation enzymes, the expression levels of genes related to metabolism, and the expression levels of sucrose transporter genes were enhanced during early seed development under drought stress; however, under prolonged drought stress, all of them decreased. These results demonstrated that drought stress enhances the capacity for unloading sucrose into seeds and activated sucrose metabolism during early seed development. At the middle and late seed filling stages, sucrose flow from leaves to seeds was diminished, and the balance of sucrose metabolism was impaired in seeds, resulting in seed mass reduction. The different regulation strategies in sucrose allocation, metabolism, and transport during different seed development stages may be one of the physiological mechanisms for soybean plants to resist drought stress.

Interactive effect of drought and cadmium stress on soybean root morphology and gene expression.

Recent climatic changes and low water availability due to unpredictable precipitation have reduced the productivity of soybean (Glycine max [L.] Merr.) cultivars. Limited information is available on how drought affects the accumulation and translocation of cadmium (Cd) by affecting soybean root. In this study, we investigated the effect of polyethylene glycol (PEG; 5% and 10%)-induced drought and Cd (0.2 and 0.5 mg L-1) stresses on soybean root morphology, Cd uptake and gene expression; plants not exposed to these stress (0% PEG and 0 mg L-1 Cd) served as a control. The results showed that drought affected roots morphology and Cd uptake. The reduction in root length, root area and root diameter and increase in catalase activity was less prominent in drought tolerant cultivars (Shennong20 and Liaodou32) than in drought sensitive cultivars (Liaodou3 and Liaodou10). Genes involved in abscisic acid (ABA) degradation, gibberellin and salicylic acid biosynthesis, hydrogen peroxide (H2O2) production and Cd transport were up-regulated, while those involved in zeatinriboside (ZR), indole 3-acetic acid (IAA) and methyl jasmonate (MeJA) biosynthesis were down-regulated under Cd and drought stress. Biosynthesis genes of gibberellin (Glyma03G019800.1), IAA (Glyma02G037600), ZR (XM_003550461.3) and MeJA (Glyma11G007600) were expressed to higher levels in drought tolerant cultivars than in drought sensitive cultivars. These genes represent potential candidates for the development of drought and Cd tolerant soybean cultivars.

Comparison of Soybean Transformation Efficiency and Plant Factors Affecting Transformation during the Agrobacterium Infection Process.

The susceptibility of soybean genotype to Agrobacterium infection is a key factor for the high level of genetic transformation efficiency. The objective of this study is to evaluate the plant factors related to transformation in cotyledonary nodes during the Agrobacterium infection process. This study selected three genotypes (Williams 82, Shennong 9 and Bert) with high transformation efficiency, which presented better susceptibility to Agrobacterium infection, and three low transformation efficiency genotypes (General, Liaodou 16 and Kottman), which showed a relatively weak susceptibility. Gibberellin (GA) levels and soybean GA20ox2 and CYP707A2 transcripts of high-efficiency genotypes increased and were higher than those of low-efficiency genotypes; however, the opposite performance was shown in abscisic acid (ABA). Higher zeatin riboside (ZR) content and DNA quantity, and relatively higher expression of soybean IPT5, CYCD3 and CYCA3 were obtained in high-efficiency genotypes. High-efficiency genotypes had low methyl jasmonate (MeJA) content, polyphenol oxidase (PPO) and peroxidase (POD) activity, and relatively lower expression of soybean OPR3, PPO1 and PRX71. GA and ZR were positive plant factors for Agrobacterium-mediated soybean transformation by facilitating germination and growth, and increasing the number of cells in DNA synthesis cycle, respectively; MeJA, PPO, POD and ABA were negative plant factors by inducing defence reactions and repressing germination and growth, respectively.

Effects of continuous cropping on fungal community diversity and soil metabolites in soybean roots.

IMPORTANCE: Soybean yield can be affected by soybean soil fungal communities in different tillage patterns. Soybean is an important food crop with great significance worldwide. Continuous cultivation resulted in soil nutrient deficiencies, disordered metabolism of root exudates, fungal pathogen accumulation, and an altered microbial community, which brought a drop in soybean output. In this study, taking the soybean agroecosystem in northeast China, we revealed the microbial ecology and soil metabolites spectrum, especially the diversity and composition of soil fungi and the correlation of pathogenic fungi, and discussed the mechanisms and the measures of alleviating the obstacles.

Continuous-cropping-tolerant soybean cultivars alleviate continuous cropping obstacles by improving structure and function of rhizosphere microorganisms.

Introduction: Soybean continuous cropping will change soil microorganisms and cause continuous cropping obstacles, resulting in a significant yield decline. Different soybean cultivars have different tolerances to continuous cropping, but the relationship between continuous cropping tolerance and soil microorganisms is not clear. Methods: Two soybean cultivars with different tolerances to continuous cropping were used to study the effects of continuous cropping on soil physical and chemical properties, nitrogen and phosphorus cyclic enzyme activities, rhizosphere soil microbial community and function. Results: The results showed that the yield reduction rate of a continuous-cropping-tolerant cultivar (L14) was lower than that of a continuous-cropping-sensitive cultivar (L10) under continuous cropping. At R1 and R6 growth stages, soil nutrient content (NH4 +-N, NO3 --N, AP, DOM, TK, and pH), nitrogen cycling enzyme (URE, NAG, LAP) activities, phosphorus cycling enzyme (ALP, NPA, ACP) activities, copy numbers of nitrogen functional genes (AOA, AOB, nirK, nirK) and phosphorus functional genes (phoA, phoB) in L14 were higher than those in L10. Soybean cultivar was an important factor affecting the structure and functional structure of bacterial community under continuous cropping. The relative abundances of Proteobacteria, Bacteroidota, Acidobacteriota and Verrucomicrobiota with L14 were significantly higher than those of L10. The complexity of the soil bacterial community co-occurrence network in L14 was higher than that in L10. Discussion: The continuous-cropping-tolerant soybean cultivar recruited more beneficial bacteria, changed the structure and function of microbial community, improved soil nitrogen and phosphorus cycling, and reduced the impact of continuous cropping obstacles on grain yield.

Proteome characterization of two contrasting soybean genotypes in response to different phosphorus treatments.

Phosphorus (P) is an essential element for the growth and development of plants. Soybean (Glycine max) is an important food crop that is grown worldwide. Soybean yield is significantly affected by P deficiency in the soil. To investigate the molecular factors that determine the response and tolerance at low-P in soybean, we conducted a comparative proteomics study of a genotype with low-P tolerance (Liaodou 13, L13) and a genotype with low-P sensitivity (Tiefeng 3, T3) in a paper culture experiment with three P treatments, i.e. P-free (0 mmol·L-1), low-P (0.05 mmol·L-1) and normal-P (0.5 mmol·L-1). A total of 4126 proteins were identified in roots of the two genotypes. Increased numbers of differentially expressed proteins (DEPs) were obtained from low-P to P-free conditions compared to the normal-P treatment. All DEPs obtained in L13 (660) were upregulated in response to P deficiency, while most DEPs detected in T3 (133) were downregulated under P deficiency. Important metabolic pathways such as oxidative phosphorylation, glutathione metabolism and carbon metabolism were suppressed in T3, which could have affected the survival of the plants in P-limited soil. In contrast, L13 increased the metabolic activity in the 2-oxocarboxylic acid metabolism, carbon metabolism, glycolysis, biosynthesis of amino acids, pentose phosphatase, oxidative phosphorylation, other types of O-glycan biosynthesis and riboflavin metabolic pathways in order to maintain normal plant growth under P deficiency. Three key proteins I1KW20 (prohibitins), I1K3U8 (alpha-amylase inhibitors) and C6SZ93 (alpha-amylase inhibitors) were suggested as potential biomarkers for screening soybean genotypes with low-P tolerance. Overall, this study provides new insights into the response and tolerance to P deficiency in soybean.

Changes in Soil Microbial Activity, Bacterial Community Composition and Function in a Long-Term Continuous Soybean Cropping System After Corn Insertion and Fertilization.

Corn-soybean rotation and fertilization are common practices improving soil fertility and crop yield. Their effects on bacterial community have been extensively studied, yet, few comprehensive studies about the microbial activity, bacterial community and functional groups in a long-term continuous soybean cropping system after corn insertion and fertilization. The effects of corn insertions (Sm: no corn insertion, CS: 3 cycles of corn-soybean rotations and CCS: 2 cycles of corn-corn-soybean rotations) with two fertilization regimes (No fertilization and NPK) on bacterial community and microbial activity were investigated in a long-term field experiment. The bacterial communities among treatments were evaluated using high-throughput sequencing then bacterial functions were predicted based on the FaProTax database. Soil respiration and extracellular enzyme activities were used to assess soil microbial activity. Soil bacterial community structure was significantly altered by corn insertions (p < 0.01) and fertilization (p < 0.01), whereas bacterial functional structure was only affected by corn insertion (p < 0.01). The activities of four enzymes (invertase, ß-glucosidase, ß-xylosidase, and ß-D-1,4-cellobiohydrolase) involved in soil C cycling were enhanced by NPK fertilizer, and were also enhanced by corn insertions except for the invertase and ß-xylosidase under NPK fertilization. NPK fertilizer significantly improved soil microbial activity except for soil metabolic quotient (qCO2) and the microbial quotient under corn insertions. Corn insertions also significantly improved soil microbial activity except for the ratio of soil induced respiration (SIR) to basal respiration (BR) under fertilization and the qCO2 was decreased by corn insertions. These activity parameters were highly correlated with the soil functional capability of aromatic compound degradation, which was the main predictors of bacterial functional structure. In general, the combination of soil microbial activity, bacterial community and corresponding functional analysis provided comprehensive insights into compositional and functional adaptations to corn insertions and fertilization.

Eight years of variations in ecosystem respiration over a residue-incorporated rotation cropland and its controlling factors.

The carbon dioxide emissions from cropland play important roles in the regional carbon budget. In this study, continuous measurements of the ecosystem respiration (RE) were obtained using the eddy covariance technique in a winter wheat-summer maize double cropping agroecosystem mainly between 2004 and 2012 in order to identify the among-year variations in RE and the related factors responsible. The annual RE, estimated by Lloyd and Taylor model, which was the most accurate, was 1866.4 ± 105.75 g C m-2 year-1 and it ranged from 1650.68 g C m-2 year-1 to 1945.57 g C m-2 year-1 during the eight years. The seasonal RE values were 867.98 ± 125.24 g C m-2 year-1 and 890.55 ± 131.34 g C m-2 year-1 for wheat and maize, respectively. Additionally, crop residue carbon ranged from 322.73 g C m-2 year-1 in 2012 and 453.49 g C m-2 year-1 in 2007. Correlation analysis indicated that the interannual variations in wheat and maize RE were correlated with the seasonal mean soil water content (W-Ws) and maximum leaf area index (W-LAImax) of wheat, and seasonal mean air temperature of maize (S-Ta), respectively. A rest method was attempted to investigate whether these relationships were occasional or inevitable. The rests of RE, i.e. the difference between simulated and observed RE values, were significantly influenced by LAI of wheat and hourly Ta of maize season but not by hourly Ws of maize season, indicating that the influence of W-LAImax and S-Ta on RE were inevitable outcomes and that of W-Ws on wheat RE was occasional. So we suggested that one should not confirm the controlling factors of interannual variations in carbon fluxes just from simple relationships, which may be statistical coincidences and do not correlated with biotical processes.

Response of Soybean Root to Phosphorus Deficiency under Sucrose Feeding: Insight from Morphological and Metabolome Characterizations.

Phosphorus (P) is one the least available essential plant macronutrients in soils that is a major constraint on plant growth. Soybean (Glycine max L.) production is often limited due to low P availability. The better management of P deficiency requires improvement of soybean's P use efficiency. Sugars are implicated in P starvation responses, and a complete understanding of the role of sucrose together with P in coordinating P starvation responses is missing in soybean. This study explored global metabolomic changes in previously screened low-P-tolerant (Liaodou, L13) and low-P-sensitive (Tiefeng 3, T3) soybean genotypes by liquid chromatography coupled mass spectrometry. We also studied the root morphological response to sucrose application (1%) in P-starved soybean genotypes against normal P supply. Root morphology in L13 genotype has significantly improved P starvation responses as compared to the T3 genotype. Exogenous sucrose application greatly affected root length, root volume, and root surface area in L13 genotype while low-P-sensitive genotype, i.e., T3, only responded by increasing number of lateral roots. Root : shoot ratio increased after sucrose treatment regardless of P conditions, in both genotypes. T3 showed a relatively higher number of differentially accumulated metabolites between P-starved and normal P conditions as compared to L13 genotype. Common metabolites accumulated under the influence of sucrose were 5-O-methylembelin, D-glucuronic acid, and N-acetyl-L-phenylalanine. We have discussed the possible roles of the pathways associated with these metabolites. The differentially accumulated metabolites between both genotypes under the influence of sucrose are also discussed. These results are important to further explore the role of sucrose in the observed pathways. Especially, our results are relevant to formulate strategies for improving P efficiency of soybean genotypes with different P efficiencies.

Effect of drought stress on sugar metabolism in leaves and roots of soybean seedlings.

Sucrose is the main photosynthetic product in plants, and acts as a major energy substrate and signaling regulator of plant growth. Furthermore, sucrose is involved in the responses to various abiotic stresses. However, the role of sucrose in soybean (Glycine max L.) growth and development under drought stress remains largely unknown. In this study, the two soybean cultivars, Shennong8 (CV.SN8) and Shennong12 (CV.SN12), were grown in pot culture and subjected to three water treatments for 15 days: soil moisture contents of 75 ±â€¯5% (CK), 45 ±â€¯5% (MD), and 30 ±â€¯5% (SD) of field capacity. Under drought stress, the reduction in shoot biomass was more pronounced than the reduction of biomass in the root of both soybean cultivars, resulting in higher root/shoot (R/S) ratio. Drought stress increased the contents of soluble sugar and sucrose in the leaves, but decreased starch content; in the roots, all of these parameters were increased. This may be related to the enhanced carbohydrate metabolism activity under drought stress, including notable changes in the activities of sugar metabolism enzymes and expression levels of GmSPS, GmSuSy, GmC-INV, GmA-INV, GmAMY3, and GmBAM1. Furthermore, the expression levels of sucrose transporter genes (GmSUC2, GmSWEET6, and GmSWEET15) in leaves and roots of soybean seedlings were up-regulated under drought stress. In conclusion, our results highlight that the increase in R/S ratio caused by the changes of sugar allocation, metabolism, and transport under drought stress contributes towards drought resistance of soybean.

MSH2 and MSH6 in Mismatch Repair System Account for Soybean (Glycine max (L.) Merr.) Tolerance to Cadmium Toxicity by Determining DNA Damage Response.

Our aim was to investigate DNA mismatch repair (MMR) genes regulating cadmium tolerance in two soybean cultivars. Cultivars Liaodou 10 (LD10, Cd-sensitive) and Shennong 20 (SN20, Cd-tolerant) seedlings were grown hydroponically on Murashige and Skoog (MS) media containing 0-2.5 mg·L-1 Cd for 4 days. Cd stress induced less random amplified polymorphism DNA (RAPD) polymorphism in LD10 than in SN20 roots, causing G1/S arrest in LD10 and G2/M arrest in SN20 roots. Virus-induced gene silencing (VIGS) of MLH1 in LD10-TRV-MLH1 plantlets showed markedly diminished G1/S arrest but enhanced root length/area under Cd stress. However, an increase in G1/S arrest and reduction of G2/M arrest occurred in SN20-TRV-MSH2 and SN20-TRV-MSH6 plantlets with decreased root length/area under Cd stress. Taken together, we conclude that the low expression of MSH2 and MSH6, involved in the G2/M arrest, results in Cd-induced DNA damage recognition bypassing the MMR system to activate G1/S arrest with the assistance of MLH1. This then leads to repressed root growth in LD10, explaining the intervarietal difference in Cd tolerance in soybean.

Environmental influences on light response parameters of net carbon exchange in two rotation croplands on the North China Plain.

The ecosystem light response parameters, i.e. apparent quantum yield (α), maximum rate of ecosystem gross photosynthesis (Amax), and daytime ecosystem respiration (Rd), are very important when estimating regional carbon budgets. But they are not well understood in double cropping systems. Here, continuous flux data were collected from two rotation croplands in Yucheng (YC) and in Luancheng (LC) to describe the among-year variations in α, Amax, and Rd, and to investigate variation mechanism on an annual scale. The three parameters exhibited marked fluctuations during the observation years. The annual α, Amax, and Rd ranged from 0.0022-0.0059 mg CO2 µmol photon-1, from 2.33-4.43 mg CO2 m-2 s-1, and from 0.19-0.47 mg CO2 m-2 s-1 at YC, and from 0.0016-0.0021 mg CO2 µmol photon-1, from 3.00-6.30 mg CO2 m-2 s-1, and from 0.06-0.19 mg CO2 m-2 s-1 at LC, respectively. Annual α and Rd declined significantly when vapor pressure deficit (VPD) exceeded 1.05 kPa and increased significantly when canopy conductance (gc) exceed 6.33 mm/s at YC, but changed slightly when VPD and gc exceeded 1.16 kPa and 7.77 mm/s at LC, respectively. The fact that the negative effects of VPD and gc on α and Rd at LC were not as significant as they were at YC may be attributed to different climate conditions and planting species. A negative relationship (R2 = 0.90 for YC and 0.89 for LC) existed between VPD and gc. Therefore, the VPD, through its negative effect on gc, inhibited α and Rd indirectly. Among-year Amax variation was mainly influenced by the annual mean surface soil temperature (Ts) of non-growing season of wheat significantly (R2 = 0.59, P < 0.01). Therefore, in future climate change scenarios, these environmental effects need to be included in carbon cycle models so that the accuracy of the carbon budget estimation can be improved.

Rapid Effect of Nitrogen Supply for Soybean at the Beginning Flowering Stage on Biomass and Sucrose Metabolism.

Nitrogen application at the beginning flowering stage (R1 stage) increased the soybean grain yield, however, the rapid effect of enriched nitrogen at R1 growth stage on soybean dry matter accumulation and sugar metabolism is still unclear. Continuous high nitrogen (CHN), Continuous low nitrogen (CLN), Enriched nitrogen supply at R1 stage (ENS) treatments were applied on two soybean cultivars (Liaodou11, Liaodou14), to investigate the effect of enriched nitrogen on plant biomass accumulation and sucrose metabolism. After 12 h of ENS treatment, the root/shoot rate of both cultivars were lower than that of CLN, but at 24 h it was no significant difference between ENS and CLN. Enriched N at R1 stage, soybean kept a balance of sucrose synthesis and decomposition in leaf by affecting sucrose synthetase (SS) and sucrose phosphate synthase (SPS) activities. Under N limitation condition the plant dry matter accumulation supported root growth priority. Enriched N at R1 stage resulted in the rapid shoot biomass accumulation. In high yield cultivar, the shoot growth was priority to root growth, the common yield cultivar was on the contrary. Our result suggest that enrich N at R1 stage resulted in the accumulation of biomass in shoot rapidly.

Shoot/Root Interactions Affect Soybean Photosynthetic Traits and Yield Formation: A Case Study of Grafting With Record-Yield Cultivars.

Improvement of soybean [Glycine max (L.) Merr.] yield and photosynthesis physiology have been achieved over decades of cultivar breeding. Identification of the mechanisms involved in shoot-root interactions would be beneficial for the development of yield improvement breeding strategies. The objectives of this study were to investigate soybean shoot-root interactions with different-year released soybean cultivars and to evaluate their effects on grain yield and yield components. Soybean grafts used in this study were constructed with two record-yield cultivars Liaodou14 (L14) and Zhonghuang35 (Z35) and eleven cultivars released in 1966-2006 from the United States and Chinese. The grafting experiments were conducted as pot-culture experiments and repeated in 2014 and 2015. Our results showed that net photosynthesis rate (P N) was positively correlated to both root activity and root bleeding sap mass (RBSM) during the R6 reproductive stage. Moreover, different year-released soybean shoots had all exhibited capabilities of changing the root activity and architecture of L14 and Z35 rootstocks to "generation"-specific patterns during all reproductive stages. However, these influences were independent of the photosynthetic strength. Yield analysis had demonstrated that high-yielding root systems (L14 and Z35 rootstocks) could cause more than 15% of yield increase in seven out of eleven common scions in a scion-genotype-dependent manner. For Williams-descendant cultivar scions, L14 and Z35 rootstocks promoted yields mainly by increasing the seed number (SN), but those scions of Amsoy-descendent cultivars showed mainly seed weight (SW) increases when grafted onto L14 and Z35 rootstocks. On the other hand, although most tested common rootstocks did not show significant influence over the final yields in record-yield L14 and Z35 scions, they were obviously capable of shifting the formation of yield components when compared to L14 and Z35 self-grafting controls. Taken together, soybean shoots could influence the root physiology and played a crucial role in the determination of yield potentials. Synergistically with shoots, soybean roots played a more supportive role during the realization of yield potentials through root activities and by balancing the formation of yield components. These findings provided interesting insightful information for developing new breeding strategies which aim to pyramid elite physiological and yield traits by selecting specific parental combinations.

5-Azacytidine promotes shoot regeneration during Agrobacterium-mediated soybean transformation.

Agrobacterium-mediated soybean transformation has been greatly improved in recent years, however the transformation efficiency is still low and highly genotype-dependent when compared to other species. Here, we characterized seventeen soybean genotypes based on their genetic transformation efficiencies, i.e., high and low, during Agrobacterium-mediated transformation. To reveal the molecular basis of this transformation difference, we constructed a highly efficient transient transgene expression system using soybean cotyledon protoplasts and then assess the methylation levels of promoter and coding regions of an EYFP (enhanced yellow fluorescent protein) gene introduced into the protoplast cultures of various soybean genotypes using BSP (bisulfite sequencing PCR). Increased methylation was found to be associated with the considerably decreased transfection efficiency (as percentage of EYFP fluorescent protoplasts) in low-efficacy genotypes as compared with those in high-efficacy on three DAT (day after transfection). 5-Azacytidine (5-Azac), a demethylating reagent commonly applied in epigenetic researches, significantly improved the transient transfection efficiency and transgene expression level in low-efficiency genotypes. Furthermore, the shoot regeneration efficiency in low-efficiency genotypes was substantially increased by 5-Azac treatment in an Agrobacterium-mediated soybean transformation system. Taken together, we concluded that lower methylation level in transgene contributed to enhanced shoot regeneration in Agrobacterium-mediated soybean transformation.

Roles of MSH2 and MSH6 in cadmium-induced G2/M checkpoint arrest in Arabidopsis roots.

DNA mismatch repair (MMR) proteins have been implicated in sensing and correcting DNA damage, and in governing cell cycle progression in the presence of structurally anomalous nucleotide lesions induced by different stresses in mammalian cells. Here, Arabidopsis seedlings were grown hydroponically on 0.5 × MS media containing cadmium (Cd) at 0-4.0 mg L-1 for 5 d. Flow cytometry results indicated that Cd stress induced a G2/M cell cycle arrest both in MLH1-, MSH2-, MSH6-deficient, and in WT roots, associated with marked changes of G2/M regulatory genes, including ATM, ATR, SOG1, BRCA1, WEE1, CYCD4; 1, MAD2, CDKA;1, CYCB1; 2 and CYCB1; 1. However, the Cd-induced G2/M phase arrest was markedly diminished in the MSH2- and MSH6-deficient roots, while a lack of MLH1 had no effect on Cd-induced G2 phase arrest relative to that in the wild type roots under the corresponding Cd stress. Expression of the above G2/M regulatory genes was altered in MLH1, MSH2 and MSH6-deficient roots in response to Cd treatment. Furthermore, Cd elicited endoreplication in MSH2- and MSH6-deficient roots, but not in MLH1-deficient Arabidopsis roots. Results suggest that MSH2 and MSH6 may act as direct sensors of Cd-mediated DNA damage. Taken together, we conclude that MSH2 and MSH6, but not MLH1, components of the MMR system are involved in the G2 phase arrest and endoreplication induced by Cd stress in Arabidopsis roots.