Genes induced by WDS are differentially expressed in two populations of aleppo pine (Pinus halepensis)

Gene expression in response to water-deficit stress (WDS) is a critical factor determining the survival and growth of pine seedlings. To understand how gene expression varies with different water stress levels, we differentially screened a cDNA library from roots of aleppo pine (Pinus halepensis) seedlings subjected to WDS. We found 156 clones of genes up-regulated and 56 down-regulated in response to WDS. Of the 14 clones selected for further characterization, 8 resemble WDS-responsive genes previously identified in angiosperms. The genes showing similarities to known proteins included an aldehyde dehydrogenase, a late embryogenesis abundant (LEA) protein, a chitinase, a cyclophilin, an MYB factor, an inorganic pyrophosphatase, a sucrose synthase, and a 4-coumarate ligase. Six of the clones did not have any similarity to previously identified proteins of known function. Quantitative polymerase chain reaction (qPCR) was used to compare the differential expression of these genes during control (no stress), moderate, and severe WDS treatments of seedling progeny from two different geographic origins within Israel, Yirka, and Beit Jann. The difference in expression between the treatments for various genes ranged from 1.9 to 8.0 cycle threshold. Most of the genes were expressed at similar levels in trees from the two populations or at higher levels in trees from Belt Jann, Israel. Northern blot analyses done for four highly expressed genes verify the results of the qPCR.