Transcriptional profiling of watermelon during its incompatible interaction with Fusarium oxysporum f. sp niveum

Transcriptome profiling of watermelon during its incompatible interactions with Fusarium oxysporum f.sp. niveum (FON) was performed using an Agilent custom microarray, which contains 15,000 probes representing approximately 8,200 watermelon genes. A total of 24, 275, 596, 598, and 592 genes showed significant differential expression in FON-infected plant roots, as compared with mock-inoculated roots, at 0.5, 1, 3, 5 and 8 days post inoculation (dpi), respectively. Bioinformatics analysis of these differentially expressed genes revealed that during the incompatible interaction between watermelon and FON, the expression of a number of pathogenesis-related (PR) genes, transcription factors, signalling/regulatory genes, and cell wall modification genes, was significantly induced. A number of genes for transporter proteins such as aquaporins were down-regulated, indicating that transporter proteins might contribute to the development of wilt symptoms after FON infection. In the incompatible interaction, most genes involved in biosynthesis of jasmonic acid (JA) were expressed stronger and more sustained than those in a compatible interaction in FON-infected tissues. Similarly, genes associated with shikimate-phenylpropanoid-lignin biosynthesis were also induced during the incompatible interaction, but expression of these genes were not changed or repressed in the compatible interaction. Those results demonstrate that JA biosynthesis and shikimate-phenylpropanoid-lignin pathways might play important roles in watermelon against FON infection and thus provides new insights in understanding the molecular basis and signalling network in watermelon plants in response to FON infection. We also performed confocal imaging of watermelon roots infected with the green fluorescent protein (GFP)-tagged FON1 to revealed histological characteristics of the infection.