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A shared gene drives lateral root development and root nodule symbiosis pathways in Lotus

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Science  22 Nov 2019:
Vol. 366, Issue 6468, pp. 1021-1023
DOI: 10.1126/science.aax2153

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Common gene yields different structures

Nodules form on legume roots to house symbiotic, nitrogen-fixing bacteria. Lateral roots, characteristic of a much broader range of plants, extend to take up nutrients and water from the soil. Soyano et al. found common ground in the developmental pathways that build nodules and lateral roots (see the Perspective by Bishopp and Bennett). Evidence from Lotus japonicus, a legume that can fix atmospheric nitrogen, shows that the nodule-forming pathway shares components with the lateral root pathway.

Science, this issue p. 1021; see also p. 953

Abstract

Legumes develop root nodules in symbiosis with nitrogen-fixing rhizobial bacteria. Rhizobia evoke cell division of differentiated cortical cells into root nodule primordia for accommodating bacterial symbionts. In this study, we show that NODULE INCEPTION (NIN), a transcription factor in Lotus japonicus that is essential for initiating cortical cell divisions during nodulation, regulates the gene ASYMMETRIC LEAVES 2-LIKE 18/LATERAL ORGAN BOUNDARIES DOMAIN 16a (ASL18/LBD16a). Orthologs of ASL18/LBD16a in nonlegume plants are required for lateral root development. Coexpression of ASL18a and the CCAAT box–binding protein Nuclear Factor-Y (NF-Y) subunits, which are also directly targeted by NIN, partially suppressed the nodulation-defective phenotype of L. japonicus daphne mutants, in which cortical expression of NIN was attenuated. Our results demonstrate that ASL18a and NF-Y together regulate nodule organogenesis. Thus, a lateral root developmental pathway is incorporated downstream of NIN to drive nodule symbiosis.

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