Interactions between hydrogen sulfide and rhizobia modulate the physiology and metabolism during water deficiency-induced oxidative defense in soybean

Hydrogen sulphide (H2S), as a new gas signal molecule, participates in the regulation of a variety of abiotic stresses in plants. However, it was unclear how H2S and rhizobia can together to affect the adaptation of soybean to water deficiency. Here, the adaptation mechanism of H2S and rhizobia in soybean to water deficiency was studied. Our results showed that H2S and rhizobia jointly enhanced leaf chlorophyll content, the relative water content (RWC) and caused an increase biomass in soybean under water deficiency. Besides, under water deficiency, H2S enhanced biomass by affecting nodule numbers and nitrogenase activity during the growth of soybean. The expression of soybean nodulation marker genes including early nodulin 40 (GmENOD40), ERF required for nodulation (GmERN), and nodulation inception genes were up-regulated by H2S and rhizobia in nodules. Moreover, the combined effect of H2S and rhizobia were proved to affect the enzyme activities and gene expression level of antioxidant, as well as osmotic protective substance under water deficiency. In addition, the metabolomics results provided that the changes of lipids and lipid-like molecules were remarkably promoted by the combined effect of H2S and rhizobia. Thus, H2S and rhizobia synergistically subsided the oxidative damage by increasing the accumulation of metabolites and strengthening the antioxidant capacity under water deficiency.

Soybean Nodulation Response to Cropping Interval and Inoculation in European Cropping Systems

To support the adaption of soybean [Glycine max (L) Merrill] cultivation across Central Europe, the availability of compatible soybean nodulating Bradyrhizobia (SNB) is essential. Little is known about the symbiotic potential of indigenous SNB in Central Europe and the interaction with an SNB inoculum from commercial products. The objective of this study was to quantify the capacity of indigenous and inoculated SNB strains on the symbiotic performance of soybean in a pot experiment, using soils with and without soybean history. Under controlled conditions in a growth chamber, the study focused on two main factors: a soybean cropping interval (time since the last soybean cultivation; SCI) and inoculation with commercial Bradyrhizobia strains. Comparing the two types of soil, without soybean history and with 1–4 years SCI, we found out that plants grown in soil with soybean history and without inoculation had significantly more root nodules and higher nitrogen content in the plant tissue. These parameters, along with the leghemoglobin content, were found to be a variable among soils with 1–4 years SCI and did not show a trend over the years. Inoculation in soil without soybean history showed a significant increase in a nodulation rate, leghemoglobin content, and soybean tissue nitrogen concentration. The study found that response to inoculation varied significantly as per locations in soil with previous soybean cultivation history. An inoculated soybean grown on loamy sandy soils from the location Müncheberg had significantly more nodules as well as higher green tissue nitrogen concentration compared with non-inoculated plants. No significant improvement in a nodulation rate and tissue nitrogen concentration was observed for an inoculated soybean grown on loamy sandy soils from the location Fehrow. These results suggest that introduced SNB strains remained viable in the soil and were still symbiotically competent for up to 4 years after soybean cultivation. However, the symbiotic performance of the SNB remaining in the soils was not sufficient in all cases and makes inoculation with commercial products necessary. The SNB strains found in the soil of Central Europe could also be promising candidates for the development of inoculants and already represent a contribution to the successful cultivation of soybeans in Central Europe.

Growth and Competitive Infection Behaviors of Bradyrhizobium japonicum and Bradyrhizobium elkanii at Different Temperatures

Growth and competitive infection behaviors of two sets of Bradyrhizobium spp. strains were examined at different temperatures to explain strain-specific soybean nodulation under local climate conditions. Each set consisted of three strains—B. japonicum Hh 16-9 (Bj11-1), B. japonicum Hh 16-25 (Bj11-2), and B. elkanii Hk 16-7 (BeL7); and B. japonicum Kh 16-43 (Bj10J-2), B. japonicum Kh 16-64 (Bj10J-4), and B. elkanii Kh 16-7 (BeL7)—which were isolated from the soybean nodules cultivated in Fukagawa and Miyazaki soils, respectively. The growth of each strain was evaluated in Yeast Mannitol (YM) liquid medium at 15, 20, 25, 30, and 35 °C with shaking at 125 rpm for one week while measuring their OD660 daily. In the competitive infection experiment, each set of the strains was inoculated in sterilized vermiculite followed by sowing surface-sterilized soybean seeds, and they were cultivated at 20/18 °C and 30/28 °C in a 16/8 h (day/night) cycle in a phytotron for three weeks, then nodule compositions were determined based on the partial 16S-23R rRNA internal transcribes spacer (ITS) gene sequence of DNA extracted from the nodules. The optimum growth temperatures were at 15–20 °C for all B. japonicum strains, while they were at 25–35 °C for all B. elkanii strains. In the competitive experiment with the Fukagawa strains, Bj11-1 and BeL7 dominated in the nodules at the low and high temperatures, respectively. In the Miyazaki strains, BjS10J-2 and BeL7 dominated at the low and high temperatures, respectively. It can be assumed that temperature of soil affects rhizobia growth in rhizospheres and could be a reason for the different competitive properties of B. japonicum and B. elkanii strains at different temperatures. In addition, competitive infection was suggested between the B. japonicum strains.

Influence of Different Tillage Systems on Soybean Nodulation and Yield in the Transylvanian Plain Conditions

The paper presents the results of research conducted during 2018-2019, regarding the root nodules formation at soybean, by applying different tillage systems, under the conditions of the Agricultural Research and Development Station Turda situated in the Transylvanian Plain.The development of root nodules in soybean differs from one variety to another, the highest value of 103 nodules/plant is recorded in the Onix variety and lower in the Cristina and Felix variety with 66 and 69 nodules respectively. Also at the weight of the nodules/plant it seems to maintain the same trend, the Onix variety (0.86 g) being superior to the other two varieties (Felix 0.83 g, Cristina 0.80 g). The highest soybean average yield was registered at the Cristina variety cultivated in the minimum tillage-chisel (2548 kg/ha) and the lowest yield at the Felix variety in the no tillage (1592 kg/ha).

Isoflavone malonyl-CoA acyltransferase GmMaT2 is involved in nodulation of soybean (Glycine max) by modifying synthesis and secretion of isoflavones

Malonyl-CoA:flavonoid acyltransferases (MaT) modify isoflavones, but only a few have been characterized for activity and assigned to specific physiological processes. Legume roots exude isoflavone malonates into the rhizosphere, where they are hydrolyzed into isoflavone aglycones. Soybean GmMaT2 was highly expressed in seeds, root hairs, and nodules. GmMaT2 and GmMaT4 recombinant enzymes used isoflavone 7-O-glucosides as acceptors and malonyl-CoA as an acyl donor to generate isoflavone glucoside malonates. GmMaT2 had higher activity towards isoflavone glucosides than GmMaT4. Overexpression (OE) in hairy roots of GmMaT2 and 4 produced more malonyldaidzin, malonylgenistin, and malonylglycitin, and resulted in more nodules than control. However, only GmMaT2 knockdown (KD) hairy roots showed reduced levels of malonyldaidzin, malonylgenistin, and malonylglycitin, and likewise, reduced nodule numbers. These were consistent with the up-regulation of only GmMaT2 by rhizobial infection, and higher expression levels of early nodulation genes in GmMaT2- and 4-OE, but lower only in GmMaT2-KD roots compared to control roots. Higher malonyl isoflavonoid levels in transgenic hairy roots were associated with higher levels of isoflavones in root exudates and more nodules, and vice versa. We posit that GmMaT2 participates in soybean nodulation by catalyzing isoflavone malonylation and affecting malonyl isoflavone secretion for activation of Nod factor and nodulation.