Description: Agronomy, Vol. 8, Pages 188: Polyaspartic Acid Improves Maize (Zea mays L.) Seedling Nitrogen Assimilation Mainly by Enhancing Nitrate Reductase Activity Agronomy doi: 10.3390/agronomy8090188 Authors: Qingyan Wang Huihui Tang Guangyan Li Hui Dong Xuerui Dong Yanli Xu Zhiqiang Dong Improvement of nitrogen use efficiency is of great importance in maize (Zea mays L.) production. In the present study, an eco-friendly growth substance, polyaspartic acid (PASP), was applied to maize seedlings grown with different nitrate (NO3−) doses by foliar spraying, aimed at evaluating its effects on maize nitrogen assimilation at both the physiological and molecular level. The results showed that PASP promoted biomass and nitrogen accumulation in maize seedlings, especially under low NO3− doses. Among different NO3− conditions, the most noticeable increase in plant biomass by PASP addition was observed in seedlings grown with 1 mmol L−1 NO3−, which was a little less than the optimum concentration (2 mmol L−1) for plant growth. Furthermore, the total nitrogen accumulation increased greatly with additions of PASP to plants grown under suboptimal NO3− conditions. The promotion of nitrogen assimilation was mostly due to the increase of nitrate reductase (NR) activities. The NR activities in seedlings grown under low NO3− doses (0.5 and 1.0 mmol L−1) were extremely increased by PASP, while the activities of glutamine synthetase (GS), aspartate aminotransferase (AspAT), and alanine aminotransferase (AlaAT) were slightly changed. Moreover, the regulation of PASP on NR activity was most probably due to the promotion of the protein accumulation rather than gene expression. Accumulation of NR protein was similarly affected as NR activity, which was markedly increased by PASP treatment. In conclusion, the present study provides insights into the promotion by PASP of nitrogen assimilation and identifies candidate regulatory enzymatic mechanisms, which warrant further investigation with the use of PASP in promoting nitrogen utilization in crops.

Description: Agronomy, Vol. 8, Pages 159: Complete Chloroplast Genome Sequence of Broomcorn Millet (Panicum miliaceum L.) and Comparative Analysis with Other Panicoideae Species Agronomy doi: 10.3390/agronomy8090159 Authors: Xiaojun Nie Xian Zhao Sue Wang Ting Zhang Chong Li Hui Liu Wei Tong Yuan Guo Broomcorn millet (Panicum miliaceum L.) is one of the earliest domesticated cereals worldwide, holding significant agricultural, historical, and evolutionary importance. However, our genomic knowledge of it is rather limited at present, hampering further genetic and evolutionary studies. Here, we sequenced and assembled the chloroplast genome (cp) of broomcorn millet and compared it with five other Panicoideae species. Results showed that the cp genome of broomcorn millet was 139,826 bp in size, with a typical quadripartite structure. In total, 108 genes were annotated and 18 genes were duplicated in the IR (inverted region) region, which was similar to other Panicoideae species. Comparative analysis showed a rather conserved genome structure between them, with three common regions. Furthermore, RNA editing, codon usage, and expansion of the IR, as well as simple sequence repeat (SSR) elements, were systematically investigated and 13 potential DNA markers were developed for Panicoideae species identification. Finally, phylogenetic analysis implied that broomcorn millet was a sister species to Panicum virgatum within the tribe Paniceae, and supported a monophyly of the Panicoideae. This study has reported for the first time the genome organization, gene content, and structural features of the chloroplast genome of broomcorn millet, which provides valuable information for genetic and evolutionary studies in the genus Panicum and beyond.

Description: Agronomy, Vol. 8, Pages 108: Is Endophyte-Plant Co-Denitrification a Source of Nitrous Oxides Emission? —An Experimental Investigation with Soybean Agronomy doi: 10.3390/agronomy8070108 Authors: Hao Sun Yuting Li Hui Xu The biological pattern of plants’ nitrous oxide (N2O) generation is not well understood because plant cells cannot form N2O from nitric oxide (NO) reduction. Hypothetically, we consider that plant-endophytic co-denitrification is potentially capable of making up for the functional loss of NO reduction in the plant cell and is thus the source of plant-derived N2O. In order to test the above hypothesis, field-cultured soybean seedlings and aseptic-cultured seedlings were used to establish plant holobionts with differentially established endophytes. The N2O fluxes, copies of the bacterial NO reductase encoding gene, and a diversity of endophytic denitrifying bacteria of these holobionts were observed by gas chromatography, real-time PCR, and 16s rDNA sequencing. The flux of N2O by the field seedlings was significantly higher than the fluxes of the aseptic seedlings and bulk soil. The N2O flux of the soybean seedlings was significantly correlated to the abundance of the bacterial NO reductase encoding gene. Eleven genera of denitrifying bacteria were observed in the soybean seedlings, and among them, two genera of aerobic denitrifying bacteria were specifically associated with colonizing plant samples. In this work we have also showed that plant N2O emission is affected by the abundance of total endophytic denitrifying bacteria. We conclude that plant sourced N2O is cooperatively generated by the plant-endophyte symbiotic system in which endophytic denitrifying bacteria help plants to emit N2O by taking over the NO–N2O reduction process.