A GENE ENCODING A HOST-SPECIFIC ELICITOR PROTEIN OF PHYTOPHTHORA-PARASITICA

Extracellular elicitor proteins (elicitins) from Phytophthora species induce local and distal defense responses specifically in plants of th e Solanaceae and Cruciferae. Based on elicitin amino acid sequences, e licitin-coding sequences from P. parasitica were amplified by the poly merase chain reaction. A genomic clone containing a complete elicitin gene, parA1, was isolated and sequenced. Elicitin was confirmed to be encoded as a precursor protein containing a 20-amino acid signal pepti de that is processed before secretion. Bacterial expression of the clo ned elicitin gene as a translational fusion protein containing glutath ione S-transferase yielded a biologically active protein capable of in ducing a hypersensitive response in tobacco, suggesting that fungus-sp ecific postranslational modifications of elicitin are not required for its activity. Southern blot analysis indicated that elicitin genes oc cur as a multigene family (at least two to 10 copies) in P. parasitica , P. capsici, P. citricola, P. citrophthora, P. cryptogea, P. drechsle ri, P. megasperma, and P. palmivora. Some isolates of P. parasitica th at did not produce elicitins still contained elicitin-coding sequences but did not accumulate elicitin mRNA.