Identification of Genes Involved in the Responses of Tangor (C. reticulata × C. sinensis) to Drought Stress

Drought is the major abiotic stress with adverse effects on citrus, decreasing the agronomical yield and influencing the fruit quality. In this study, cDNA-amplified fragment length polymorphism (cDNA-AFLP) technique was used to investigate the transcriptional profile changes and identify drought-responsive genes in "Amakusa" tangor (C. reticulata × C. sinensis), a hybrid citrus sensitive to water stress. The 255 out of 6,245 transcript-derived fragments (TDFs) displayed altered expression patterns including (A) induction, (B) repression, (C) upregulation, and (D) downregulation. With BLAST search, the gene products of differentially expressed fragments (DEFs) could be classified into several categories: cellular processes, transcription, transport, metabolism, stress/stimuli response, and developmental processes. Downregulated genes were highly represented by photosynthesis and basic metabolism, while upregulated ones were enriched in genes that were involved in transcription regulation, defense, energy, and transport. Present result also revealed some transient and up- and then downregulated genes such as aquaporin protein and photosystem enzyme. Expression patterns of 17 TDFs among 18 homologous to function-known genes were confirmed by qRT-PCR analysis. The present results revealed potential mechanism of drought tolerance in fruit crop and also provided candidate genes for future experiments in citrus.