Year: 1990
Type: dissertation
Abstract: A gene library of Pseudomonas syringae pathovar phaseolicola (the causal agent of Phaseolus vulgaris bean halo blight) race 3B strain 1302A was constructed in the cosmid pLAFR3.The library was screened for the presence of genes which could alter cultivar-specific pathogeni city.No clones containing genes for virulence were identified, but two clones conferred avirulence towards cultivar Tendergreen.A shared 1.4 kb fragment was identified as responsible for these symptoms on pod and leaf tests.Probing to other isolates of JP.s_.phaseolicola with an internal 0.86 kb fragment revealed the presence of a highly homologous chromosomal sequence only in strains avirulent on Tendergreen and in the pathovar glycinea.There was strong homology to an avirulence gene from race 3A (also avirulent on Tendergreen) with some restriction fragment length polymorphism.Neither avirulence gene induced avirulence on bacteria in Ph. acutifolius 1072, the plant used to differentiate races 3A and 3B, and so are probably alleles.A hypersensitive response resulted when the cloned DNA was present in different bacterial or plant backgrounds, provided the Tendergreen race 3 resistance gene was present.The avirulence gene was sequenced and site-specific mutagenesis implicated the largest ORF (633 bp) as the avirulence gene.Eh coli-like transcription/translation signals were absent, pseudomonad-like promoters were present.The putative protein of 22.8 kD had no signals for secretion nor areas of membrane affinity.Preliminary attempts to express the proteins were inconclusive.There was no homology to proteins or DNA sequences (including other aviru lence genes) in data banks.The function of the avirulence gene product remains unknown.IWien you know a thing, to hold that you know it; and when you do not know a thing, to allow that you do not know itthis is knowledge.
Source: Spiral (Imperial College London)
Author: Carol E. Jenner
Language: English
Subfield: Plant Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2759735258