MtLAX2, a functional homologue of the auxin influx transporter AUX1, is required for nodule organogenesis

Nodules are specialized structures that form symbiotic, nitrogen-fixing associations with rhizobia on some plants including Medicago truncatula. Previous work has shown that auxin signalling is involved in nodule formation. Roy et al. extend this knowledge through the identification of a Medicago gene encoding MtLAX2 that is a functional homologue of the Arabidopsis auxin influx transporter AUX1. Loss of function mutants mtlax2 and aux1 show similar phenotypes including reduced sensitivity to auxin, reduced lateral root number, and reduced root gravitropism. Furthermore, MtLAX2 is expressed at very early stages of nodule formation and is required for nodule initiation. This study indicates that auxin influx is crucial for both nodule and lateral root organogenesis, and provides additional insights into the process of nodule formation. Plant Physiol. 10.​1104/​pp.​16.​01473