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GhWRKY17, A WRKY Transcription Factor From Cotton,is Involved In ABA Signaling And Drought, Salt Stress Response

Posted on:2014-04-06Degree:MasterType:Thesis
Country:ChinaCandidate:H R YanFull Text:PDF
GTID:2250330425977179Subject:Biochemistry and Molecular Biology
Abstract/Summary:PDF Full Text Request
Plants being sessile are adversely affected by unfavorable environmental conditionsduring their development, such as drought, high salinity, nutrient starvation, wound, high orlow temperature and pathogen attack. Among them, drought and high salinity are two majorstress conditions that impose constraints on plant growth and development and thus mayreduce crop productivity. Plants have evolved elaborate and intricate mechanisms to achieveoptimal adaption to these unfavorable stress conditions. Stress signaling and transcriptionalmodulation are vital aspects of the complex genetic and biochemical networks that plants useto respond to stress. Transcription factors, such as DREB, NAC, WRKY, MYB, are one of themost important defence-related proteins. WRKY is a recently discovered superfamily oftranscription factors existing abroad in plants. WRKY proteins specifically bind to the W-boxin target gene promoters to regulate the plant development and adaptation to diverseenvironmental stresses. There is a large body of evidence demonstrating that specific WRKYproteins are key regulators in the basal defense responses. Although numbers of studies haveunraveled the role of WRKY transcription factors in abiotic stress response, the elucidation ofthe molecular mechanisms underlying the plant regulatory response remains largely unclear,particularly in non-model plants, including economically important crops. Here, we isolatedan ABA-hypersensitive group IId WRKY gene, GhWRKY17, from cotton (G. hirsutum L.)and characterized the function and regulation of this protein. The main results are as follows:(1) The full-length cDNA sequence is1,104bp and contains a complete open readingframe (ORF) of957bp, which encodes a318-amino acid protein with an estimated molecularmass of34.773kDa and an isoelectric point of9.87. Sequence analysis showed that thededuced protein has a single WRKY DNA-binding domain and a conserved primaryC-terminal motif shared by group IId WRKY superfamily members. A phylogenetic tree clustered the putative protein with the group IId WRKY proteins. This protein shows highsequence similarity with Arabidopsis WRKY17, and thus designed as GhWRKY17. Thecoding region of GhWRKY17is interrupted by two introns. GhWRKY17is organized as asingle-copy gene in the cotton genome.(2) By using inverse PCR (I-PCR), a1,163-bp fragment of the GhWRKY17promoterwas isolated. PlantCARE databases predicted various cis-elements including tissue-specificand development-related elements as well as abiotic stress responsive andpathogen/elicitor-related elements.(3) The GhWRKY17protein is localized in the nucleus, specifically binds to W-box, andAgrobacterium-mediated transactivation assay demonstrated that GhWRKY17functions as atranscriptional activator.(4) Semi-quantitative RT-PCR revealed that the expression of GhWRKY17can beinduced by abiotic stresses, including drought, salt, wounding and cold. In addition, signalingmolecules such as ABA and H2O2can also up-regulate the GhWRKY17transcript.(5) Overexpression of GhWRKY17enhanced plant sensitivity to drought and salt stress.During the seed germination, when ABA biosynthesis inhibitor was added the drought andsalt sensitivity phenotypes in the transgenic lines disappeared. The result suggest that theinvolving of GhWRKY17in drought and salt stress is ABA-related.(6) Overexpressing GhWRKY17enhanced plant sensitivity to ABA-mediated seedgermination and post-germinative growth, but impaired ABA-induced stomatal closure, thusresult in higher rate of water loss. These results suggest that GhWRKY17is involved in ABAsignaling and drought stress response.(7) Under drought and salt stress, transgenic plants exhibited more accumulation of ROSand serious membrane damage. Activities of antioxidant enzymes, including SOD, POD,CAT and APX and proline contents in transgenic lines were lower than those in wild typeplants, suggesting that GhWRKY17confers response to drought and salt stress through thecontrol of cellular ROS production.(8) GhWRKY17transgenic plants were sensitive to oxidative stress.
Keywords/Search Tags:Cotton (G. hirsutum L.), WRKY transcription factor, drought and salt stress, ABA signaling, ROS
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