Abstract
Phosphite, an analogue of phosphate, is widely used to control oomycete diseases of plants. It inhibits growth and zoospore production in species such as Phytophthora cinnamomi both in vitro and in planta. As an approach to understanding the mechanism of phosphite on P. cinnamomi we compared the transcriptomes of untreated and phosphite-treated mycelium using microarray analysis to identify genes that are differentially expressed. A cDNA library was constructed using RNA from phosphate treated mycelium and used to construct an array containing over 9,000 clones as probes. The array was hybridised with differentially labelled RNA from untreated and phosphite-treated mycelium. From the arrays seventy-two transcripts with altered patterns in gene expression (change ≥ 2 fold) were identified. Forty five clones represented genes that were down-regulated with changes in gene expression ranging from 2- to 3.5-fold. Thirty-two cDNA transcripts were up-regulated with changes in gene expression ranging from 2- to 16-fold. The identity of the most highly expressed clones was determined by sequencing and comparison with sequences in GenBank.