Identification and Expression Analysis of Salinity-induced Genes in Rangpur lime (Citrus limonia)

Among the economically important horticultural crops, citrus is one of the most vulnerable crops to soil salinity. Rangpur lime is more tolerant to high soil salinity than other commonly used citrus rootstocks. However, the molecular mechanism involved in salinity tolerance has not been explored in Rangpur lime. In this study, a cDNA library was constructed from leaves of Rangpur lime watered for 30 days with 100 mmol.L-1 NaCl in tap water or tap water using suppression subtractive hybridization (SSH). Two hundred cDNA clones randomly selected from this library were sequenced, and an average of 569 bp was obtained from the majority of clones. Fifty-six salinity-induced genes, showing 2- to 6-fold increases in their expression levels, were identified by macroarray hybridizations. Salinity-induced genes were associated with transcription (5.36%), stress response and signaling (21.43%), metabolism (16.07%), transport facilitation (10.71%), photosynthesis (10.71%), protein synthesis and fate (19.64%) and cellular biogenesis (3.57%). Stress response- and signaling-related genes constituted the largest functional group, associated with the production of compatible solutes, regulation of stomatal movement, lipid modification, oxidative stress, antioxidant defense, and stress signaling. Expression levels of 13 identified genes were induced 1.8- to 3.1-fold, which were validated in salt-treated and untreated Rangpur lime. The functions of salinity-induced, stress-related genes and their potential roles in salinity tolerance in Rangpur lime were discussed.