Differentially expressed genes in resistant and susceptible Pistacia vera L. Cultivars in response to Pseudomonas fluorescens and Phytophthora parsiana

Gummosis (Phytophthora root and crown rot) is an important and destructive disease that affects fruit trees like pistachio (Pistacia vera L.). Although many studies have been performed on the possibility of biological control of gummosis, up to now few studies have been done on transcriptionally induced resistance genes in pistachio against Phytophthora disease. In the present research, the cDNA-AFLP method was used to analyze the transcriptionally regulated genes during the interaction between susceptible (Sarakhs) and resistant (Badami-Rize Zarandi) pistachio cultivars with Pseudomonas fluorescens and/or Phytophthora parsiana. Using 12 AFLP primer combinations, approximately 740 different cDNA-AFLP fragments with sizes ranged from 50 to 700 bp were generated for susceptible and resistant pistachio cultivars. Forty six TDFs (transcript derived fragments) were then selected for susceptible cultivar and 24 TDFs for resistant cultivar. Accordingly, each one of these TDFs was recognized by similarity search using the BlastX program against the NCBI GenBank nucleotide database. Notably, 18.5% of TDFs were hypothetical or uncharacterized proteins and 1.4% of them indicated no significant similarity to the known genes. Among the TDFs with known function, disease resistance proteins were identified, which were newly regulated in response to pathogen or rhizobacterium. Furthermore, we found that the expression level of different growth-regulatory or defense-related genes was higher after the exposure to Pseudomonas fluorescens and/or Phytophthora parsiana. To better understand the defense mechanism of pistachio plants and recognition of P. fluorescens-activated genes, which induce resistance against P. parsiana, would significantly assist in the development of new resistant pistachio cultivars.