The secret of NIN (Nodule Inception) ($) (Plant Cell)

Twenty years ago, a genetic screen of Lotus japonicas identified NIN (NODULE INCEPTION), a transcription factor required for both early (infection thread) and late (nodule primordium development) stages of nodule formation. In daphne (a weak allele of NIN), infection threads form but not nodule primordia, suggesting that the NIN gene is only partially effective and that its two functions are separable. In this new work, Liu et al. figured out the mystery of NIN‘s regulation. They identified FN8113, another mutant in which infection thread formation and nodule formation are uncoupled; like daphne, FN8113 has a chromosome insertion several (4 – 7) kb upstream of the NIN start codon. Further analysis demonstrated that there are key transcriptional regulatory elements located far upstream of the start codon that are required for cytokinin-responsive NIN expression and nodule formation, and incorporation of these far-upstream regions allowed functional complementation of nin mutants. (Summary by Mary Williams) Plant Cell 10.1105/tpc.18.00478