Positive and Negative Regulators of Root and Nodule Development in Response to Nitrogen Availability

Plants - having to process information without brains - have evolved complex intercellular regulatory systems including regulatory peptide signalling to regulate growth, development and responses to their environment. Here, we describe regulatory peptides that is involved in the modulation of root, nodule and shoot development in response to nitrate limitations. In Arabidopsis, upon overexpression or exogenous application of CEP (C-TERMINALLY ENCODED PEPTIDE) peptides reduce root growth in a receptor dependent manner. A T-DNA insertion mutant shows the opposite phenotype, producing a larger root system under nitrate limitations through regulating G1 to S phase transition of the cell cycle in the root meristem. In Medicago truncatula, CEP peptide suppresses lateral root development and enhance root nodule formation and nitrogen fixation. The CEP peptide mediated enhancement of nodulation is partially tolerant to nitrate levels that suppress nodulation. We have isolated and identified several CEP peptides in vivo and have found that peptide activity differs according to the peptide’s post-translational modifications. On the other hand, nodule specific CLE (CLAVATA 3/ENDOSPERM SURROUNDING REGION related) peptides inhibit nodulation in a receptor dependent manner mediated through long distance signalling. Overall, our work suggests signalling peptides are important positive and negative regulators of root development and nodulation, and provides a link between nitrogen demand signalling and developmental programs.