Genetic dissection of the initiation of the infection process and nodule tissue development in the Rhizobium-pea (Pisum sativum L.) symbiosis

Twelve non-nodulating pea (Pisium sativum L.) mutants were studied to identify the blocks in nodule tissue development. In nine, the reason for the lack of infection thread (IT) development was studied; this had been characterized previously in the other three mutants. With respect to IT development, mutants in gene sym7 are interrupted at the stage of (c) under bar olonization of the pocket in the curled (r) under bar oot (h) under bar air (Crh(-) phenotype), mutants in genes sym37 and sym38 are blocked at the stage of (IT) under bar growth in the root (h) under bar air cell (Ith(-) phenotype) and mutants in gene sym34 at the stage of (IT) under bar growth inside root cortex cells (Itr(-) phenotype). With respect to nodule tissue development, mutants in genes sym7, sym14 and sym35 were shown to be blocked at the stage of (c) under bar ortical (c) under bar ell (d) under bar ivisions (Ccd(-) phenotype), mutants in gone sym34 are halted at the stage of (n) under bar odule (p) under bar rimordium (NP) (d) under bar evelopment (Npd(-) phenotype) and mutants in genes sym37 and sym38 are arrested at the stage of nodule (m) under bar eristem development (Nmd(-) phenotype). Thus, the sequential functioning of the genes Sym37, Sym38 and the gene Sym34 apparently differs in the infection process and during nodule tissue development. Based on these data, a scheme is suggested for the sequential functioning of early pea symbiotic genes in the two developmental processes: infection and nodule tissue formation. (C) 2002 Annals of Botany Company.