Identification of drought response genes in Zygophyllum xanthoxylum by suppression subtractive hybridization

Drought is an important abiotic stress that seriously limits plant growth and crop productivity in some regions of the world. Zygophyllum xanthoxylum, a succulent xerophyte species with excellent adaptability to adverse arid environments, is an excellent model system for the study of the molecular mechanisms behind drought tolerance in xerophytic species. To better understand the molecular basis of Z. xanthoxylum responses to drought stress and to isolate drought tolerance-related genes from Z. xanthoxylum, we constructed a cDNA library from Z. xanthoxylum and screened the library for stress-related genes by PCR-based suppression subtractive hybridization (SSH). A total of 637 expressed sequence tags were generated by sequencing 672 randomly selected clones, resulting in the identification of 338 unigenes comprising 77 contigs and 261 singlets. The unigenes were assigned to 13 functional categories, such as metabolism, disease- or defense-related genes and energyrelated gene. In addition, we analyzed the expression patterns of 24 genes associated with drought stress-responsive pathways by real-time RT-PCR. The results indicated that osmolyte biosynthesis genes, reactive oxygen scavengers, transporters, signaling components and transcription factors play important roles in drought stress responses. This study provides a valuable resource for studying the drought tolerance mechanism of this xerophytic plant species.