| Leaf senescence is natural phenomena and ubiquitious in plants, which is not a simplydegenerative process, but a type of programmed cell death at organ level. Senescence iscrucial for formation of production and is not only influenced by the regulation of endogenousgene expression, but also induced by various environmental factors. Thus, an understandingof senescence has significant effects on crop production and quality. Cytokinin, as oneimportant type of plant hormone, has extensive biological functions, including promoting celldivision, releasing apical dominace, breaking seed dormancy, developing of stem and shootand delaying leaf senescence.The expression of the exogenous isopentenyl transferase (IPT)gene in plants results in an increased level of endogenous cytokinin in senescing leaves anddelaying plants senescence.In the present study, transgenic cotton lines of IPT gene were used as material. Geneexpression profiles of transgenic cotton lines and azygous cotton lines (Zhongmian10) wereperformed using Solexa sequencing. After analysis of experiment datas, the mechanismunderlying cytokinins delaying senescence was mainly defined. The results were as follows:1. Using Solexa sequencing, we obtained about6,183,347and5,766,375raw tags andidentified224,617and200,071distinct clean tags after removal of low quality tags oftransgenic and azygous cotton lines, respectively.2. Though analysis of copy number distribution of distinct clean tags,4.78%of thedistinct tags with copy number>100, while82.34%of the distinct tags with copy numberbetween2and20were obtained in transgenic cotton lines. In azygous cotton lines, thepercentages were4.80%and81.86%. All clean tags were aligned to the TIGR cotton databasefor gene annotation.65.57%and63.42%of clean tags of transgenic and azygous cotton lineswere mapped to the reference genes, respectively.3. We obtained1,334differentially expressed genes between transgenic cotton lines andazygous cotton lines. Analysis of differentially expressed genes revealed719and499 significantly up-regulated and down-regulated genes. Additionally, there were75and40differential expressed genes only expressed in transgenic and azygous cotton lines,respectively. Though analysis of differentially expressed genes,35differentially expressedgenes in response to endogenous cytokinin during leaf senescence were identified, includinggenes involving cytokinin signal transduction (2), genes involving transcriptional regulation(8), genes involving plant hormones signal transduction (4) and genes involving metabolism(21).4. Relative expression levels of17differentially expressed genes, which were randomlyselected, were detected by qRT-PCR and GhACTI gene were selected as internal control gene.Expression patterns of seleted genes were mainly agreed with Solexa sequencing and it wasbasically comfirmed the reliability of sequencing data.5. After pathway enrichment analysis of differentially expressed genes, we identified thatcytokinin delayed plant leaf senescence through flavone biosynthesis, arginine and prolinemetabolism, glyoxylate and dicarboxylate metabolism, and eukaryotic RNA degradationpathways.6. After Gene Ontology enrichment analysis of differentially expressed genes, thebiological processes of cytokinin delaying plant leaf senescence were identified, includingpyrimidine nucleoside triphosphate biosynthetic and metabolic process, response to hormonestimulus process, response to auxin stimulus process, regulation of hydrolase activity process,response to endogenous stimulus process, cellular biosynthetic process. |
