Figure 10.

Model of miR172 node regulation in common bean-rhizobia symbiosis. Positive regulation is represented with arrows and negative regulation with lines. The root signaling cascade, triggered by rhizobial NF, is essential for rhizobia infection and nodule development in different legumes. Regulation of common bean rhizobial infection and nodulation by miR172c and AP2-1 are represented by dashed arrows or lines. A high level of miR172c (thick line) induces AP2-1 degradation (hatched circle), while active AP2-1 (circle) is present when the miR172c level is very low (thin line). miR172c positively regulates early nodulation gene expression and rhizobial infection, silencing AP2-1 that may repress ENOD40 expression. Nodule number is positively regulated by miR172c; AON decreases through low RIC1/NIC1 expression, perhaps regulated by AP2-1. In mature nodules, abundant miR172c silences AP2-1, an activator of senescence-related genes that are further required during nodule senescence when AP2-1 levels are recovered. ACCO, Aminocyclopropane carboxylase oxidase.