The Medicago SymCEP7 hormone increases nodule number via shoots without compromising lateral root number.

Legumes acquire soil nutrients through nitrogen-fixing root nodules and lateral roots. To balance the costs and benefits of nodulation, legumes negatively control root nodule number by autoregulatory and hormonal pathways. How legumes simultaneously coordinate root nodule and lateral root development to procure nutrients remains poorly understood. In Medicago (Medicago truncatula), a subset of mature C-TERMINALLY ENCODED PEPTIDE (CEP) hormones can systemically promote nodule number, but all CEP hormones tested to date negatively regulate lateral root number. Here we showed that Medicago CEP7 produces a mature peptide, SymCEP7, that promotes nodulation from the shoot without compromising lateral root number. Rhizobial inoculation induced CEP7 in the susceptible root nodulation zone in a Nod factor-dependent manner, and, in contrast to other CEP genes, its transcription level was elevated in the ethylene signaling mutant sickle. Using mass spectrometry, fluorescence microscopy and expression analysis, we demonstrated that SymCEP7 activity requires the COMPACT ROOT ARCHITECTURE 2 receptor and activates the shoot-to-root systemic effector, miR2111. Shoot-applied SymCEP7 rapidly promoted nodule number in the pM to nM range at concentrations up to five orders of magnitude lower than effects mediated by root-applied SymCEP7. Shoot-applied SymCEP7 also promoted nodule number in White Clover (Trifolium repens) and Lotus (Lotus japonicus), which suggests that this biological function may be evolutionarily conserved. We propose that SymCEP7 acts in the Medicago shoot to counter balance the autoregulation pathways induced rapidly by rhizobia to enable nodulation without compromising lateral root growth, thus promoting the acquisition of nutrients other than nitrogen to support their growth.

Refinement of the subunit interaction network within the nucleosome remodelling and deacetylase (NuRD) complex.

The nucleosome remodelling and deacetylase (NuRD) complex is essential for the development of complex animals. NuRD has roles in regulating gene expression and repairing damaged DNA. The complex comprises at least six proteins with two or more paralogues of each protein routinely identified when the complex is purified from cell extracts. To understand the structure and function of NuRD, a map of direct subunit interactions is needed. Dozens of published studies have attempted to define direct inter-subunit connectivities. We propose that conclusions reported in many such studies are in fact ambiguous for one of several reasons. First, the expression of many NuRD subunits in bacteria is unlikely to lead to folded, active protein. Second, interaction studies carried out in cells that contain endogenous NuRD complex can lead to false positives through bridging of target proteins by endogenous components. Combining existing information on NuRD structure with a protocol designed to minimize false positives, we report a conservative and robust interaction map for the NuRD complex. We also suggest a 3D model of the complex that brings together the existing data on the complex. The issues and strategies discussed herein are also applicable to the analysis of a wide range of multi-subunit complexes. ENZYMES: Micrococcal nuclease (MNase), EC 3.1.31.1; histone deacetylase (HDAC), EC 3.5.1.98.