Analysis of differentially expressed genes in Curcuma amada and Zingiber officinale upon infection with Ralstonia solanacearum by suppression subtractive hybridization

Bacterial wilt, one of the major diseases in ginger is caused by Ralstonia solanacearum and lack of resistant genotype adds constraints to the crop improvement programs and for the management of bacterial wilt. Curcuma amada is a potential donor for bacterial wilt resistance to Zingiber officinale, if the exact mechanism of resistance is understood. In this study, a PCR-based suppression subtractive hybridization (SSH) was used to identify C. amada genes that are differentially and early expressed in response to the R. solanacearum infection compared to Z. officinale. A forward subtracted library of differentially expressed genes was synthesized by cloning DNA fragments (300-1,200 bp) from subtracted sample and sequenced. Upon computational analysis of the 150 SSH clones sequenced, 119 produced suitable sequences of high homology with the genes of known functions. These were classified into three potential functional categories: proteins involved in biological processes (31 %), cellular component (43 %) and molecular function (26 %). Among these differentially expressed genes, sequences coding for putative proteins related to defense response (high homology between 85 and 100 % identity) were, cell wall-associated hydrolase, xyloglucan transglycosylase (XTG), cytochrome P 450, metallocarboxypeptidase inhibitor, peroxiredoxin, nitrilase-associated protein, leucine-rich protein (LRR) and glutathione-S-transferase (GST). The three transcripts were discriminative: expression of LRR, GST and XTG was much higher in resistant species (C. amada) than in susceptible species (Z. officinale) at every time point. The isolated ESTs reported here contribute to improve our understanding about this plant-pathogen interaction.