Isolation and analysis of defense-related genes in infected sorghum seedlings

Abstract

To understand the key processes governing defense mechanisms in Sorghum bicolor upon infection by fungus Colletotrichum sublineolum, the causal agent of sorghum anthracnose, a cDNA library was constructed using the suppression subtractive hybridization (SSH) method. SSH was performed between cDNAs prepared from a resistant sorghum cultivar (DK18) inoculated with C. sublineolum and uninoculated control samples. A total of 41 unique cDNA clones were found differentially expressed in inoculated seedlings. They can be classified into 7 categories according to characterized or putative functions of their homologous sequences. These genes are potentially involved in plant defense, signal transduction, abiotic stress, secondary metabolism, protein synthesis and degradation. Gene expression patterns were compared in sorghum cultivars that are resistant or susceptible to the anthracnose pathogen following inoculation. In addition, expression of the pathogen-inducible genes was investigated in sorghum seedlings after challenges by non-host pathogens including Cochliobolus heterotrophus and Magnaporthe grisea. Selected sorghum genes were over-expressed in transgenic tobacco plants which were demonstrated to show enhanced resistance against Pseudomonas syringae pv. tabaci. Elevated expression levels of PR genes were recorded in the transgenic plants. Further characterization and functional analysis of these genes may allow us to identify sorghum genes that can be utilized for board-spectrum disease resistance in different plant species.