Two opposing pathways independently regulate symbiotic nodulation in Medicago truncatula ($) (Plant Physiol)

To optimize usage of nutrient, legumes utilize multiple strategies to regulate root nitrogen-fixing symbiotic nodulation. Excessive nodulation may hamper plant’s normal growth, so fine-tuning it is important for plant survival. Laffont et al. report that there are two independent pathways systematically regulating symbiotic nodulation in Medicago truncatula. They found that Super Numeric Nodule (SUNN) and Compact Root Architecture 2 (CRA2) systemic pathways act antagonistically and lead to weakened and enhanced nodulation capacity of roots, respectively. However, they also showed that these two pathways have little genetic interaction and act independently. This study shows that Medicago truncatula has evolved a sophisticated mechanism to balance nutrient distribution in the symbiotic relationship between itself and rhizobia. (Summarized by Nanxun Qin) Plant Physiology 10.1104/pp.18.01588