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It is unclear how elevated CO2 (eCO2) and warming interactively influence soil N mineralization in the rhizosphere of rice (Oryza sativa L.), given that the N mineralization process in anaerobic paddy soils differs from that of aerobic upland soils. In this study, we conducted a rhizobox experiment in open top chambers and used 15N-13C dual-labeling to examine the impacts of eCO2 (700 ppm) and warming (2 °C above the ambient) on N mineralization and associated microbial processes in the rhizosphere of rice plants under anaerobic conditions. Compared to the control, the combination of eCO2 and warming increased rice N uptake by 50% in a no-added-N treatment and 32% under an N-added treatment, with the additional uptake mainly consisting of soil-derived N. Co-elevation of CO2 and temperature increased microbial biomass C and N and increased N mineralization by 41% and 23% in the no-added-N and N-added treatments, respectively. The absolute abundances of the N-mineralization genes chiA, pepA, pepN, and urea hydrolysis gene ureC in the rhizosphere increased by 22–30% under eCO2 and warming, corresponding to the additional N mineralization and photosynthetic C allocation into the soil. However, eCO2 plus warming did not increase the metabolic efficiency of N mineralization (mineralized N per unit microbial N). Our results suggest that the co-elevation of CO2 and temperature stimulated microbially mediated soil N mineralization in the rhizosphere of rice, posing a risk on the acceleration of soil organic matter decomposition. [ABSTRACT FROM AUTHOR]

Phytophthora root and stem rot in soybean (Glycine max) is a destructive disease worldwide, and hence improving crop resistance to the causal pathogen, P. sojae , is a major target for breeders. However, it remains largely unclear how the pathogen regulates the various affected signaling pathways in the host, which consist of complex networks including key transcription factors and their targets. We have previously demonstrated that GmBTB/POZ enhances soybean resistance to P. sojae and the associated defense response. Here, we demonstrate that GmBTB/POZ interacts with the transcription factor GmAP2 and promotes its ubiquitination. GmAP2 -RNAi transgenic soybean hairy roots exhibited enhanced resistance to P. sojae , whereas roots overexpressing GmAP2 showed hypersensitivity. GmWRKY33 was identified as a target of GmAP2, which represses its expression by directly binding to the promoter. GmWRKY33 acts as a positive regulator in the response of soybean to P. sojae. Overexpression of GmBTB/POZ released the GmAP2-regulated suppression of GmWRKY33 in hairy roots overexpressing GmAP2 and increased their resistance to P. sojae. Taken together, our results indicate that GmBTB/POZ-GmAP2 modulation of the P. sojae resistance response forms a novel regulatory mechanism, which putatively regulates the downstream target gene GmWRKY33 in soybean. [ABSTRACT FROM AUTHOR]

Summary: Phytophthora sojae is a destructive pathogen of soybean [Glycine max (L.) Merr.] which causes stem and root rot on soybean plants worldwide. However, the pathogenesis and molecular mechanism of plant defence responses against P. sojae are largely unclear. Herein, we document the underlying mechanisms and function of a novel BTB/POZ protein, GmBTB/POZ, which contains a BTB/POZ domain found in certain animal transcriptional regulators, in host soybean plants in response to P. sojae. It is located in the cell nucleus and is transcriptionally up‐regulated by P. sojae. Overexpression of GmBTB/POZ in soybean resulted in enhanced resistance to P. sojae. The activities and expression levels of enzymatic superoxide dismutase (SOD) and peroxidase (POD) antioxidants were significantly higher in GmBTB/POZ‐overexpressing (GmBTB/POZ‐OE) transgenic soybean plants than in wild‐type (WT) plants treated with sterile water or infected with P. sojae. The transcript levels of defence‐associated genes were also higher in overexpressing plants than in WT on infection. Moreover, salicylic acid (SA) levels and the transcript levels of SA biosynthesis‐related genes were markedly higher in GmBTB/POZ‐OE transgenic soybean than in WT, but there were almost no differences in jasmonic acid (JA) levels or JA biosynthesis‐related gene expression between GmBTB/POZ‐OE and WT soybean lines. Furthermore, exogenous SA application induced the expression of GmBTB/POZ and inhibited the increase in P. sojae biomass in both WT and GmBTB/POZ‐OE transgenic soybean plants. Taken together, these results suggest that GmBTB/POZ plays a positive role in P. sojae resistance and the defence response in soybean via a process that might be dependent on SA. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Although the effect of elevated CO 2 (eCO 2 ) 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 CO 2 levels, this potentially threatens the nutritional content and quality of food crops. Using four soybean cultivars, we assessed the effects of eCO 2 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, eCO 2 had no influence on soybean seed protein and oil concentrations. At R8, eCO 2 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 eCO 2 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 eCO 2 . Compared with ambient CO 2 , the concentrations of K, Ca, Mg, P, and S increased significantly under eCO 2 at R6, while the Fe concentration decreased significantly. The response of Zn and Mn concentrations to eCO 2 varied among cultivars. At R8 and under eCO 2 , Mg, S, and Ca concentrations increased significantly, while Zn and Fe concentrations decreased significantly. These findings suggest that eCO 2 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 eCO 2 varied between cultivars.

Nitrogen deficiency limits crop performance under elevated CO 2 (eCO 2 ), depending on the ability of plant N uptake. However, the dynamics and redistribution of N 2 fixation, and fertilizer and soil N use in legumes under eCO 2 have been little studied. Such an investigation is essential to improve the adaptability of legumes to climate change. We took advantage of genotype-specific responses of soybean to increased CO 2 to test which N-uptake phenotypes are most strongly related to enhanced yield. Eight soybean cultivars were grown in open-top chambers with either 390 ppm (aCO 2 ) or 550 ppm CO 2 (eCO 2 ). The plants were supplied with 100 mg N kg -1 soil as 15 N-labeled calcium nitrate, and harvested at the initial seed-filling (R5) and full-mature (R8) stages. Increased yield in response to eCO 2 correlated highly ( r = 0.95) with an increase in symbiotically fixed N during the R5 to R8 stage. In contrast, eCO 2 only led to small increases in the uptake of fertilizer-derived and soil-derived N during R5 to R8, and these increases did not correlate with enhanced yield. Elevated CO 2 also decreased the proportion of seed N redistributed from shoot to seeds, and this decrease strongly correlated with increased yield. Moreover, the total N uptake was associated with increases in fixed-N per nodule in response to eCO 2 , but not with changes in nodule biomass, nodule density, or root length.