Inducible system for lateral roots in Arabidopsis thaliana and maize.

The study of biological processes contributing to plant growth can be complicated by the small number of cells involved and by the brief and sudden appearance of some crucial developmental steps. Given such troublesome circumstances, methods to monitor the timing or to increase the number of concerned cells can be of great advantage to researchers. Lateral root initiation is a process taking place endogenously in a discrete number of cells of the parent root. It represents the onset of the formation of a new meristem and provides the below ground part of the plant the ability to react on environmental conditions such as nutrient and water availability. Insights into the underlying mechanisms of this developmental event can be of major importance to provide means of improving tolerance to nutrient and water deficient conditions. The exact timing and site of lateral root initiation are, however, impossible to predict, hampering exhaustive studies of the sequence of events directing this process. Here, we present a method to synchronize the induction of lateral roots in Arabidopsis thaliana and maize. By initially preventing the formation of laterals in young seedlings and subsequently inducing lateral root initiation, this method not only allows controlling the process in time but also enlarges significantly the population of cells involved, opening up the way to systems biology approaches.

Auxin influx activity is associated with Frankia infection during actinorhizal nodule formation in Casuarina glauca.

Plants from the Casuarinaceae family enter symbiosis with the actinomycete Frankia leading to the formation of nitrogen-fixing root nodules. We observed that application of the auxin influx inhibitor 1-naphtoxyacetic acid perturbs actinorhizal nodule formation. This suggests a potential role for auxin influx carriers in the infection process. We therefore isolated and characterized homologs of the auxin influx carrier (AUX1-LAX) genes in Casuarina glauca. Two members of this family were found to share high levels of deduced protein sequence identity with Arabidopsis (Arabidopsis thaliana) AUX-LAX proteins. Complementation of the Arabidopsis aux1 mutant revealed that one of them is functionally equivalent to AUX1 and was named CgAUX1. The spatial and temporal expression pattern of CgAUX1 promoter:beta-glucuronidase reporter was analyzed in Casuarinaceae. We observed that CgAUX1 was expressed in plant cells infected by Frankia throughout the course of actinorhizal nodule formation. Our data suggest that auxin plays an important role during plant cell infection in actinorhizal symbioses.