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

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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