NAD-malic enzyme affects nitrogen fixing activity of Bradyrhizobium Japonicum USDA 110 bacteroids in soybean nodules

• Main Authors: Tan Van Dao, Mika Nomura, Rie Hamaguchi, Kensuke Kato, Manabu Itakura, Kiwamu Minamisawa, Suphawat Sinsuwongwat, Hoa Thi Phuong Le, Takakazu Kaneko, Satoshi Tabata, Shigeyuki Tajima
• Format: Journal
• Published: 2018
• Subjects: Agricultural and Biological Sciences
• Online Access: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=57149121759&origin=inward; http://cmuir.cmu.ac.th/jspui/handle/6653943832/60033
• Institution: Chiang Mai University

The NAD+-dependent malic enzyme (DME) has been reported to play a key role supporting nitrogenase activity in bacteroids of Sinorhizobium meliloti. Genetic evidence for a similar role in Bradyrhizobium japonicum USDA110 was obtained by constructing a dme mutant. Soybean plants inoculated with a dme mutant did not show delayed nodulation, but formed small root nodules and exhibited significant nitrogen-deficiency symptoms. Nodule numbers and the acetylene reducting activity per nodule as a dry weight value 14 and 28 days after inoculation with the dme mutant were comparable to those of plants inoculated with wild-type B. japonicum. However, shoot dry weight and acetylene reducting activity per nodule decreased to ca. 30% of the values in plants with wild-type B. japonicum. The sucrose and organic acid (malate, succinate, acetate, a-ketoglutarate and lactate) contents of the nodules were investigated. Amounts of sucrose, malate and a-ketoglutarate increased on inoculation with the dme mutant, suggesting that the decreased DME and nitrogenase activities in the bacteroids resulted in a reduction in the consumption of these respiratory metabolites by the nodules. The data suggest that the DME activity of B. japonicum bacteroids plays a role in nodule metabolism and supports nitrogen fixation.