Transcriptional profiling of Impatiens walleriana genes through different stages of downy mildew infection reveals novel genes involved in disease susceptibility

Abstract

Impatiens downy mildew is a highly destructive disease of Impatiens walleriana, an economically important bedding ornamental crop. This disease is caused by a recently emerged pathogen Plasmopara obducens. Since both the host and pathogen are relatively less studied, there are only a few genomic resources available for both I. walleriana and P. obducens. In this study, we have analyzed transcriptional changes in I. walleriana in response to P. obducens infection during different stages of disease development. Our main goal was to identify candidate genes that may be involved in I. walleriana susceptibility to P. obducens. Since the genome of I. walleriana is not available publicly, we constructed and optimized a de novo transcriptome assembly consisting of 73,022 transcripts. Differential expression analysis based on this optimized de novo transcriptome assembly revealed 3,000 to 4,500 differentially expressed transcripts (DETs) at six different time points during infection. Functional annotation of these DETs revealed that numerous plant stress responsive genes are activated and deactivated throughout the infection cycle. Several receptor-like kinases (RLKs), resistance genes, powdery mildew susceptibility genes, transcription factors including a grape downy mildew susceptibility factor, several retrotransposons and many other plant stress related genes were predominantly differentially expressed in I. walleriana in response to P. obducens. Analyses reported here provide molecular insights into the disease susceptibility mechanism of the Impatiens downy mildew and lays out a strong foundation for future studies aimed at improving downy mildew resistance in I. walleriana.

Keywords

• plant-pathogen interaction transcriptome
• impatiense downy mildew
• plasmopora obducens
• susceptibility genes