Ectopic expression of the AmDREB1F gene from Ammopiptanthus mongolicus enhances stress tolerance of transgenic Arabidopsis / 生物工程学报

Dehydration-responsive element binding proteins (DREBs) are an important class of transcription factors related to plant stress tolerance. Ammopiptanthus mongolicus is an evergreen broadleaf shrub endemic to desert areas of northwest China, and it has a very high tolerance to harsh environments. In order to reveal the functions and mechanisms of the AmDREB1F gene from this species in enduring abiotic stresses, we performed subcellular localization test, expression pattern analysis, and stress tolerance evaluation of transgenic Arabidopsis harboring this gene. The protein encoded by AmDREB1F was localized in the nucleus. In laboratory-cultured A. mongolicus seedlings, the expression of AmDREB1F was induced significantly by cold and drought but very slightly by salt and heat stresses, and undetectable upon ABA treatment. In leaves of naturally growing shrubs in the wild, the expression levels of the AmDREB1F gene were much higher during the late autumn, winter and early spring than in other seasons. Moreover, the expression was abundant in roots and immature pods rather than other organs of the shrubs. Constitutive expression of AmDREB1F in Arabidopsis induced the expression of several DREB-regulated stress-responsive genes and improved the tolerance of transgenic lines to drought, high salinity and low temperature as well as oxidative stress. The constitutive expression also caused growth retardation of the transgenics, which could be eliminated by the application of gibberellin 3. Stress-inducible expression of AmDREB1F also enhanced the tolerance of transgenic Arabidopsis to all of the four stresses mentioned above, without affecting its growth and development. These results suggest that AmDREB1F gene may play positive regulatory roles in response to abiotic stresses through the ABA-independent signaling pathways.

Construction and sequence analysis of a drought-induced full-length cDNA library from Ammopiptanthus mongolicus / 生物工程学报

Ammopiptanthus mongolicus shows very strong resistance to severe environments. To isolate drought-resistant genes and elucidate drought-resistant molecular mechanisms of the plant, we constructed a drought-induced full-length cDNA library using SMART (Switching mechanism at 5'-end of RNA transcript) technique. The phage titer of the unamplified library was 1.6 x 10(7) PFU/mL; the recombination percentage was 97.7%; and the sizes of most cloned cDNA fragments were around 1 kb. Three thousand positive clones were randomly selected and sequenced from their 5' ends, and a total of 1 450 Unigenes were identified. By Blast searches against the Nt, Nr and Swissprot databases, we found that 919 Unigenes (amount to 63.4%) showed significant similarity to the annotated genes, and the remaining 531 Unigenes (amount to 36.6%) represented novel genes without any annotation. Among the functional categories of the GO (Gene Ontology) classification, the terms related to physiological process, cellular process, binding, catalytic activity and cellular components were dominant. The next abundant terms were for organelle, protein complex, transporter activity and structural molecule activity. In addition, there were a significant proportion of the terms involved in stimulus response, gene expression regulation, regulation of physiological and biochemical processes and signal transduction. Many of the annotated Unigenes were found to be related to plant resistance to abiotic stresses, and expression analyses of 6 out of these genes by semi-quantitive RT-PCR confirmed their involvements in the response of A. mongolicus to drought stress. These results laid a foundation for the expression profile analysis and the cloning and characterization of drought-resistant genes from the plant in the future.