| Plants are sessile organisms hence they cannot escape unfavourable environmentalconditions within their life cycle, such as high salinity, drought, waterlog, high or lowtemperature, pathogen attack and mechanical agitation. For long-term evolution, plants haveevolved finely tuned stress signaling and resistance mechanisms. Understanding themechnisms of plant stress responses and adaptation to enrionmental cues is very important inthe improvement of yield and quality of crops.Effect of heterologous eicosadienoic acid and eicosatrienoic acid on physiologicalchanges in ArabidopsisThe very long chain (≥C20) polyunsaturated fatty acids (VLCPUFAs), such aseicosapentaenoic acid (EPA) and docosapentaenoic acid (DHA), are essential for humanhealth and nutrition. They can be synthetized in human, but the productivity is very low. Oilyfish is good source for these fatty acids. However, the depletion of marine fish resources andenvironmental pollution result in severe shortage of fish oil. Therefore, various attempts havebeen carried out to engineer oilseed crops, such as canola, soybean and flax, to produce thesevery long chain polyunsaturated fatty acids with some success. However, before introducingthese crop plants to agriculture, the roles of VLCPUFAs in transgenic plants such asphysiological changes and tolerance to abiotic stressed have to be evaluated. This will providevital information for the commercialization of VLCPUFA-producing transgenic plants.Homozygous single-copy transgenic Arabidopsis plants expressing the IgASE1, in whichEDA and ETrA was produced, were used for this study. We compared the difference betweentransgenic Arabidopsis and wild type in their morphology and responses to abiotic stress andbelow are our findings: (1) We carried out RT-PCR to detect the transcript level of IgASE1from rosette leavesand the result showed that IgASE1was indeed expressed in these transgenic plants. We nextmeasured the total fatty acid content in the leaf tissue by gas chromatography and the resultshowed that the transgenic plants contained two additional fatty acids conresponding to EDAand ETrA compared to the wild type. The result of the total fatty acid content in the leaf tissueshowed that these two fatty acids accumulated to25.6mol%of total fatty acids. We measuredthe total fatty acids in membranes and showed that these two fatty acids were found inmembrane of transgenic plant and the accumulation of unsaturated fatty acids was up to73.7mol%of the total fatty acids and compared to59.6mol%in the wild type plant.(2) Compared to the wild type Arabidopsis, we found the transgenic plant growed slowerduring seedling stage and the leaves were smaller. The flowers of the transgenics were smallerwith smaller petals that appear to be translucent. Seeds of the transgenic plants were largerand less dormant than the wild-type.(3) To test the sensitiveness of transgenic Arabidopsis to ABA, given the importance ofABA in the abiotic stress adaptation, the germination, early seedling growth and stomatalopening of wild-type and transgenic Arabidopsis were compared. The result showed that thetransgenic seedlings were hypersensitive to ABA during germination, early seedlingdevelopment and stomatal closing.(4) We mimicked the drought condition by treating three-day-old seedlings of both thewild-type and the transgenics with glycerol or mannitol for7days. Three weeks old plantswere subjected to drought stress by withholding water for22days. These results indicate thatthe transgenic plant exhibited enhanced drought tolerance than the wild-type Arabidopsis. Todetermine whether the drought tolerance of35S:IgASE1transgenics is due to ABA, wecompared the expression profiles by quantitative qRT-PCR of some drought-inducible genesin ABA-dependent and ABA-independent pathways. The result showed that both theABA-dependent and the ABA-independent drought-inducible genes displayed increasedtranscript levels in the transgenic plant during drought stress, implying that the adaption todrought stress in the EDA and ETrA producing transgenics involves both the ABA-dependentand ABA-independent pathways.（5）Exogenous application of EDA and ETrA can mimick the ABA and drought responses in wild type plants similar to that found in transgenic plants. These results indicatedthe involvement of these eicosapolyenoic acids in the regulation of ABA mediated seedgermination, early seedling development as well as in responses to drought of the matureplants, at least partially.Global analysis of XB3-like protein family in plantsProteins in the same family share homology domains or sequences and are relatives inevolution. Therefore, global analysis of a protein family is conduceivable in the study of theirfunction and evolution. With the rapid development of DNA sequencing technology, the fullor partial genome sequences of more than50plant species have been completed or ongoing.Therefore, it is feasible to analyze a protein family in a large number of plants.In Oryza sativa，XB3is a substrate for the XA21serine and threonine kinase and isnecessary for Xa21-mediated immunity. In Arabidopsis, five homologos genes have beennamed XBAT31, XBAT32, XBAT33, XBAT34, XBAT35, respectively. So far, XBAT32andXBAT35have been reported played roles in plant growth and development and stresstolerance. We analysed the domains of the proteins’ sequences using tools and found that allthe proteins contained ankyrin repeats (ANK) and a conserved C3HC4RF domain. Then wenamed the proteins contained ankyrin repeats (ANK) and conserved C3HC4RF domain theXB3-like proteins. We used bioinformatics methods to gather extensive information regardingthis family in the29plant genomes that have been completely sequenced. Then the functionand evolution of these proteins were studied, and the interesting gene will be found and used.(1) Using bioinformatics methods, we identified187proteins which contain ANK and aconserved C3HC4RF domain, from29species with complete genomes and named theseproteins the XB3-like proteins because they are structurally related to the rice (Oryza sativa)XB3and the encoding genes the XB3-like gene. In this study, we observed that the XB3-likegene family originated from the ferns and were identified in27species of land plants (noXB3-like gene in Chlamydomonas reinhardtii or Volvox carteri).（2）To clarify the phylogenetic relationship among the XB3-like genes and to infer theevolutionary history of the gene family, the full-length protein sequences of the XB3-likefamily members in plants were used to construct a joint unrooted phylogenetic tree, from which it can be observed that the proteins fell into three major groups (group I to group III)with well-supported bootstrap values. Interestingly, we found that the C3HC4-type RFdomain was conserved in each group. In addition, most plants contain3groups of XB3-likegenes, except for Ricinus communis and Medicago truncatula, which only contains group IXB3-like genes.（3）To investigate the expression profile of the XB3-like gene family in plants, we usedbioinformatics methods to gather extensive microarray information regarding this family inthe model plant Arabidopsis and in other crops (Oryza sative, Zea mays and Glycine max).These results demonstrated that the accumulation of XB3-like gene transcripts wasdemonstrated during different developmental stages and in different tissues. It is suggestedthat the XB3-like proteins may be play roles in during different development stages and indifferent tissues.(4) To investigate the potential function of the XB3-like gene family in plant, wesurveyed the responses of XB3-like genes to phytohormones and in Arabidopsis and Zea maysusing real-time PCR. The results demonstrated that phytohormones and mimic abiotic stressesaffect the expression of XB3-like genes and suggest that these proteins may play roles ingrowth and development as well as responses to abiotic stresses in plants.(5) Then we are interested in XBAT31, because the expression of XBAT31was inducedby all phytohormones and mimic abiotic stresses tested. Upstream of the gene2Kb sequencepromoter was used to promote the expression of GUS reporter gene. And the result showedthat XBAT31were expressed in different tissues, especially high expression in stems, leavesand inflorescence.(6) We compared the responses to salt stress between wild type and RNAi mutant, inwhich the expression of XBAT31was less than in wild type, during germination and seedlinggrowth. The result showed that the mutants couldn’t tolerate the salt stress. To determinewhether the less tolerance of mutants was dependent ABA, we compared the expressionprofiles by quantitative qRT-PCR of some of abiotic-induced genes in ABA-dependentpathway and ABA-independent pathway. The result showed that the transcript level ofABA-independent genes was reduced in mutants, and that will be part of reason for lesstolerance in mutants than wild type Arabidopsis. Therefore, we hypothesized that the XBAT31may play a positive role in response to salt stress signal. |
PDF Full Text Request