Excavation And Identification Of Abiotic Stress-resistant Genes Of The Terrestrial Cyanobacterium Nostoc Flagelliforme

The terrestrial cyanobacterium Nostoc flagelliforme is mainly distributed in arid or semiarid steppes of the western and west-northern parts of China.It shows remarkable resistance to desiccation,high and low temperature,and intense ultraviolet radiation(UV)radiation.It serves as a good material for excavation and identification of abiotic stress-resistant genes.Based on the genome sequencing of N.flagelliforme in our laboratory,we first performed transcriptome analysis of this organism in response to three abiotic stresses(i.e.dehydration,low temperature and UV-B radiation)and preliminarily conducted cluster analysis.Those up-regulated genes were divided into several groups inlcuding genes involved in signal transduction,redox,transportation,synthesis and metabolism of sugar,lipid,protein,vitamins and secondary metabolites,and process of genetic information.Besides,We chose 42 up-regulated genes for further identification via transgenic means.Successfully,37 transgenic Anabaena sp.PCC 7120 strains were obtained and further subjected to short-term treatments by mannitol,NaCl and methyl viologen(MV)stresses.By detecting photosynthetic parameter Fv/Fm,we preliminarily obtained nine strains with resistance to osmotic stress,six strains with resistance to salt stress,and six stains with resistance to MV-induced oxidative stress.Finally,we focused on NfCrtO gene which codes a putative ?-carotene ketolase.NfCrtO transgenic strain showed no resistance to long-term salt stress and low temperature.The assay of growth curve found that NfCrtO could obviously enhance the osmotic resistance of transgenic strains.The pigment composition was also analyzed by High Performance Liquid Chromatography.The result showed that NfCrtO transgenic strain had lower?-carotene/chlorophyll a ratio than control under osmotic stress,but had higher echinenone/chlorophyll a and canthaxanthin/chlorophyll a ratios.NfCrtO could also confer enhanced tolerance to UV-B radiation.For dehydration treatment,NfCrtO transgenic strain was placed on solid BG11 plates,as compared to control strain.After a long-term drying process,the former could recover physiological activity after rewetting,while the control strain died.Taken together,these results indicate that NfCrtO could enhanc the resistance to some abiotic stresses,potentially by catalyzing ?-carotene to echinenone and canthaxanthin.In addition,we also attempted to transfer these candidate genes into rice to evaluate their application potential,which was conducted with our cooperative institute.