THE PLANT CELL, Vol 1, Issue 1 65-72, Copyright © 1989 by American Society of Plant Biologists
A Non-nodulating Alfalfa Mutant Displays neither Root Hair Curling nor Early Cell Division in Response to Rhizobium meliloti
M. E. Dudley and S. R. Long
Department of Biological Sciences, Stanford University, Stanford, California 94305-5020
The early events in the alfalfa-Rhizobium meliloti symbiosis include
deformation of epidermal root hairs and the approximately concurrent
stimulation of cell dedifferentiation and cell division in the root inner
cortex. These early steps have been studied previously by analysis of R.
meliloti mutants. Bacterial strains mutated in nodABC, for example, fail to
stimulate either root hair curling or cell division events in the plant
host, whereas exopolysaccharide (exo) mutants of R. meliloti stimulate host
cell division but the resulting nodules are uninfected. As a further
approach to understanding early symbiotic interactions, we have
investigated the phenotype of a non-nodulating alfalfa mutant, MnNC-1008
(NN) (referred to as MN-1008). Nodulating and non-nodulating plants were
inoculated with wild-type R. meliloti and scored for root hair curling and
cell divisions. MN-1008 was found to be defective in both responses. Mutant
plants inoculated with Exo- bacteria also showed no cell division response.
Therefore, the genetic function mutated in MN-1008 is required for both
root hair curling and cell division, as is true for the R. meliloti nodABC
genes. These observations support the model that the distinct cellular
processes of root hair curling and cell division are triggered by related
mechanisms or components, or are causally linked.