Identification and characterization of up-regulated genes in the halophyte Limoniastrum monopetalum (L.) Boiss grown under crude oil pollution

Differential display method was applied to transcripts extracted from leaves of Limoniastrum monopetalum to identify genes that are differentially expressed in response to crude oil pollution. The results showed that 201 bands with different molecular sizes were differentially expressed in polluted plants. Ten cDNA bands were considered to be consistently over-expressed under crude oil stress and selected for sequencing. Comparative analysis of these cDNA sequences allowed us to classify them into six categories: (1) enzymes increase its activity under petroleum stress and were a good marker of petroleum stress (e.g. xanthine dehydrogenase, metallothionein type 2, and arginine decarboxylase), (2) nitrogen metabolism (e.g. glutamine synthetase and amidophosphoribosyltransferase), (3) drought genes (e.g. CPRD2), (4) salinity stress (e.g. retrotransposon protein), (5) plant growth (e.g. aminocyclopropane-1-carboxylic acid and ribulose-1,5-bisphosphate carboxylase oxygenase), and (6) transport related genes like proton-dependent oligopeptide transport (POT) family protein. Coincidently with the differential display results, the amount of the total protein differed significantly between unpolluted and polluted plants (T = 3.687, P < 0.006). The electrophoretic patterns (SDS–PAGE) for water soluble proteins revealed that 11 peptides with different molecular masses disappeared and eight different peptides were synthesized in polluted plants. The results of up-regulated genes identified in this study may explain the way that L. monopetalum populations established on the crude oil polluted soil and vigorous vegetative growth of adult plants.