Editorial: Early signaling in the rhizobium-legume symbiosis.

The initiation of the rhizobium-legume symbiosis requires localization of the bacteria to potential 33 infection sites on host roots. In this process, rhizobial chemotaxis and motility play a relevant role.The reviews by Aroney et al. and Compton and Scharf revised some important concepts related to 35 motility and chemotaxis and the preferred attractants of several model rhizobia. Aroney et al. 36 highlighted the importance of understanding chemotaxis and motility in legume symbionts, 37 especially under the environmental conditions found in the field. This, together with the 38 identification of different compounds sensed through the chemotaxis systems in each rhizobial 39 species, might predict symbiotic performance based on specific environmental conditions and root 40 exudate composition, making the selection of elite inoculants more accurate. 41The role of (iso)flavonoids as chemoattractants in rhizobia is not clear. However, they are crucial 42 The inter-kingdom signaling between rhizobia and legumes is complex and additional players, 87 which might not be essential for nodulation but could contribute to fine-tune some aspects of the 88