Gene expression in susceptible and disease resistant interactions of peas induced with Fusarium solani pathogens and chitosan

A first step for establishing the molecular basis of disease resistance in plants may be to identify genes whose expression closely follows the events occurring during infection. Nine pea clones were available from a prior screening of a cDNA library, developed from a single population of pea mRNA induced 8 h following inoculation with Fusarium solani f. sp. phaseoli. Transcription and accumulation of RNA homologous to these clones were compared over a 48 h infection course following the treatment of pea pods with either compatible or incompatible forms of F. solani or chitosan, a minor component of the fungal cell wall which is known to induce disease resistance. The incompatible reaction of the pea tissue is clearly distinguished from the compatible reaction on the basis of gene expression. Three of the cloned genes, designated Group I clones, show a large induction of their RNAs in disease resisting tissue which temporally correlates with the resistance observed cytologically. In the compatible reaction activation of Group I genes is commonly weaker or delayed, and is suppressed 12–24 h after inoculation, compared with the incompatible reaction. Genes homologous with Group II clones showed only a partial fit to the activity expected for resistance genes. We propose that selecting cloned genes whose time course of induction matches the response of plant issue to infection is a useful preliminary screening technique towards obtaining gene candidates for cross-species transformation experiments.