Isolation of ethylene-insensitive soybean mutants that are altered in pathogen susceptibility and gene-for-gene disease resistance

Plants commonly respond to pathogen infection by increasing ethylene produc tion, but it is not clear if this ethylene does more to promote disease sus ceptibility or disease resistance. Ethylene production and/or responsivenes s can be altered by genetic manipulation. The present study used mutagenesi s to identify soybean (Glycine max L. Merr.) lines with reduced sensitivity to ethylene. Two new genetic loci were identified, Etr1 and Etr2. Mutants were compared with isogenic wild-type parents for their response to differe nt soybean pathogens. Plant lines with reduced ethylene sensitivity develop ed similar or less-severe disease symptoms in response to virulent Pseudomo nas syringae pv glycinea and Phytophthora sojae, but some of the mutants de veloped similar or more severe symptoms in response to Septoria glycines an d Rhizoctonia solani. Gene-for-gene resistance against P. syringae expressi ng avr-Rpt2 remained effective, but Rps1-k-mediated resistance against P. s ojae races 4 and 7 was disrupted in the strong ethylene-insensitive etr1-1 mutant. Rps1-k-mediated resistance against P. sojae race 1 remained effecti ve, suggesting that the Rps1-k locus may encode more than one gene for dise ase resistance. Overall, our results suggest that reduced ethylene sensitiv ity can be beneficial against some pathogens but deleterious to resistance against other pathogens.