by Wending Li
ASPS Travel Awards Recipients for ComBio2015
PhD candidate, Centre for Carbon, Water and Food, Faculty of Agriculture and Environment, The University of Sydney
My research focuses on understanding ammonium transport in maize. In agricultural plant production, nitrogen fertilisers are used widely where ~1011 kg of nitrogen fertilizers are used annualy (Glass, 2003). The cultivation of cereals (wheat, maize, barley, rice) requires a significant amount of nitrogen fertiliser. Unfortunately, cereal N fertiliser use is poor, where only 30-50% of the total N applied is actually used for the production of the final grain yield (Raun and Johnson, 1999; Tilman et al., 2002). Low nitrogen use efficiencies can result in the loss of nitrogen into the environment, which causes water and soil pollution as well as greenhouse gas production (Masclaux-Daubresse et al., 2010). In addition, the waste of nitrogen fertilizers also gives rise to financial losses to the farmers, a significant cost in the production cycle. Therefore, improving plant nitrogen use efficiency (NUE) is an important strategy to overcome many of these constraints. One direction in enhancing NUE in plants is to increase the efficiency of root N transport processes. This includes, the proteins involved in the uptake of nitrogen from the soil as well as the internal storage and redistribution of nitrogen required to support growth and final seed yield and quality (Garnett et al., 2009).
Ammonium is a major form of nitrogen absorbed by plants and can be redistributed through high and low affinity pathways. The physiological and molecular activities of high-affinity ammonium transporters have been examined in numerous plant species, which belong to the AMT/MEP/Rhesus superfamily. Conversely, molecular information about low-affinity ammonium transport systems remains limited. Recently, our lab has discovered a new family of low affinity ammonium transport proteins called AMF1 (ammonium facilitator 1) (Chiasson et al., 2014). Through sequence homology, we found two AMF1 homologs in maize, which are ZmAMF1;1 and ZmAMF1;2. I have been investigating the function of these two genes in maize as well as using heterologous expression systems (yeast and Xenopus laevis oocytes) to define their functional relevance in nitrogen transport and overall plant growth. In maize, I’ve observed ZmAMF1 is induced by nitrogen starvation in roots, while both ZmAMF1 and ZmAMF2 are preferentially expressed in the shoots. The cellular location of both genes is currently being identified using a native promoter::GUS fusion construct transformed into the dwarf maize inbred line Gaspe. I have undertaken a reverse genetics approach in maize using a collection of Mu transposon insertion lines within exon and promoter loci of either ZmAMF1 or ZmAMF2 (provided by B. Meeley, DuPont Pioneer). We have progressed the transposon lines through a series of backcrosses to B73 and Gaspe using a diagnostic PCR screening assay. Mutant plants containing perturbations in ammonium transport in maize are undergoing characterisation. This project will contribute to a better understanding of the role AMF1 proteins in plant N transport and metabolism, including their role as low-affinity ammonium transporters. Our research will improve our understanding of nitrogen uptake and redistribution in plants, whiles also establishing new strategies to improve nitrogen use efficiency, plant growth and development.
Reference:
Chiasson DM, Loughlin PC, Mazurkiewicz D, Mohammadidehcheshmeh M, Fedorova EE, Okamoto M, McLean E, Glass AD, Smith SE, Bisseling T (2014) Soybean SAT1 (Symbiotic Ammonium Transporter 1) encodes a bHLH transcription factor involved in nodule growth and NH4+ transport. Proceedings of the National Academy of Sciences 111: 4814-4819
Garnett T, Conn V, Kaiser BN (2009) Root based approaches to improving nitrogen use efficiency in plants. Plant, cell & environment 32: 1272-1283
Glass AD (2003) Nitrogen use efficiency of crop plants: physiological constraints upon nitrogen absorption. Critical Reviews in Plant Sciences 22: 453-470
Masclaux-Daubresse C, Daniel-Vedele F, Dechorgnat J, Chardon F, Gaufichon L, Suzuki A (2010) Nitrogen uptake, assimilation and remobilization in plants: challenges for sustainable and productive agriculture. Annals of Botany 105: 1141-1157
Raun WR, Johnson GV (1999) Improving nitrogen use efficiency for cereal production. Agronomy Journal 91: 357-363
Tilman D, Cassman KG, Matson PA, Naylor R, Polasky S (2002) Agricultural sustainability and intensive production practices. Nature 418: 671-677
