ARS | Publication request: Identification of genes involved in the pathogenic interaction between an antagonistic strain of Pichia fermentans and peach fruit

Submitted to: Annual International Plant & Animal Genome Conference
Publication Type: Abstract Only
Publication Acceptance Date: November 30, 2009
Publication Date: N/A

Technical Abstract: A biofilm-forming strain of Pichia fermentans was very effective in reducing brown rot and grey rot in artificially wounded apple fruit when co-inoculated with either Monilinia fructicola or Botrytis cinerea, respectively. The same strain, however, was an aggressive pathogen when inoculated on peach fruit, causing decay of fruit tissues, even in the absence of other pathogens. Optical and scanning electron microscopy showed that P. fermentans produces only yeast-like shaped cells during colonization of apple tissue, while exhibiting pseudohyphal growth on peach tissue. This "Jekyll-and-Hyde" behaviour suggests that antagonists need to be thoroughly vetted prior to use as biocontrol agents. A rapid subtractive hybridization approach was used to identify differentially expressed genes in the pathogenic form of P. fermentans by comparing the cDNA of P. fermentans sampled after 24 hours growth on apple with the cDNA of the same strain grown 24 h on peach fruit. A total of 450 clones were analysed by a reverse Northern blotting technique, yielding 20 fragments which were significantly expressed on peach but not on apple tissue. These sequences were compared to the available genome sequences of another dimorphic yeast, Candida albicans. The genes most differentially expressed during the interaction with peach tissues were related to a putative hsp70 chaperone, a succinate-CoA ligase subunit, a putative pyruvate kinase, a protein similar to NADP-glutamate dehydrogenase, an acetolactate synthase, a phosphoglycerate kinase, and a glutathione peroxidase. Additional genes are being identified. The relationship between these genes, dimorphism, and pathogenicity will be discussed.