Functional analysis of genes involved in the regulation of soybean nodulation

MB Zhang1, A Tollenaere1, S Ho1, AH Hastwell1, HN Su1,2, XT Chu1, DX Li1, PM Gresshoff1 and BJ Ferguson1

  1. Centre for Integrative Legume Research, School of Agricultural and Food Sciences, The University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia
  2. National Navel Orange Engineering Research Center, Gannan Normal University, Ganzhou, Jiangxi 341000, China

The world is currently relying on the massive consumption of synthetic nitrogen fertilisers to maintain sufficient food production; however, this unsustainable agricultural practice is expensive and is leading to serious environmental pollution. Legume-rhizobia associated biological nitrogen fixation (BNF) via nodulation can alleviate this problem by reducing our dependence on the use of synthetic fertilisers. Therefore, a better understanding of nodule organogenesis and its regulation is important to help enhance the benefits of BNF gained from legumes. The autoregulation of nodulation (AON) process is a systemic mechanism in which rhizobia-induced CLE peptides are produced in the roots and transported to the shoots, where they induce a signal for the negative feedback of continued nodule development. Nodulation is also regulated locally by external factors, such as high soil nitrogen content. In soybeans (Glycine max), three nodulation-suppressive CLE peptide encoding genes have been identified; two elicited by rhizobium inoculation (GmRIC1 and GmRIC2) and one by nitrate treatment (GmNIC1). The rhizobium-responsive CLE genes are differentially expressed, but their overexpression results in a similar level of nodulation-inhibition. The expression of GmNIC1 is correlated with nitrate concentration, and a 50% reduction in nodule number is achieved with constitutive expression. Each of these three nodulation-suppressing genes has a duplicate copy as a result of soybean undergoing a duplication event roughly 13 million years ago. Findings regarding the extent of expression and tissue-specific activity of each of these six genes will be presented.