| As the developing of agriculture and industry, the discharge of "the three wastes" and longrun of chemical fertilizer and pesticide increase the content of heavy metals such as lead in the ploughhorizon, which not only restrict the normal growth and development of maize, but also endanger the health of animals and humans through the deliver of food chain. Plant microRNA (miRNA) is a kind of single stranded and noncoding small RNA that range in length from roughly21to24nucleotides. By complementary base pairing with target mRNA, miRNA may cut mRNA or restrain their translation in the post-transcriptional level, which play important roles for stress responses as well as growth and development. Maize can tolerate lead well, and the expanding of molecular biology theories and experiment technologies make it possible to identificate miRNA and their targets related to lead stress, discover the mechanism of lead absorb\translocation and resistance induced by miRNA. It has instructional significance for the breeding of cultivars with high resistance to lead and major contribution for the remission of food crisis in the worldwide.Our group had carried out deepsequencing for the root in the seedling stage of line9782which was sentitive to lead stress, and analysed expressions of some miRNA which differed a lot under the lead stress and normal condition through bioinformatics. According to previous results, this study chose maize inbred lines178and9782as materials, which have different accumulation levels of lead. By proceeding real-time quantitative PCR for candidate root miRNA and semiquantitative RT-PCR for predicted target genes, determination of catalase activities for main antioxidases under lead stress and normal condition, these results were obtained:1. The expression of miR168b in line178and miR28a*in line9782were induced under lead stress, while miR156b in line178and miR51*in line9782were downregulated. The expression levels of miR28a*, miR51*and miR156new*changed a lot in the roots of178and9782under lead stress, which showed a regulation mechanism of them to lead stress.2. The results of functional prediction showed that the known conservative miRNA with different expression levels under lead stress tended to target transcription factors such as GRAS, ARF, bZIP and SBP-box. These target genes presented different expression models under lead stress, which involved in many biological processes such as growth and development, transcriptional regulation, stress response and signal transduction.3. The study indicated that these miRNA in roots under lead stress may involved in several biological processes. For example:miR167involved in auxin signal transduction, miR166d involved in stress response; miR171involved in growth and development; miR168involved in feedback regulation.4. Analysis to SOD and POD activities in roots and leaves under lead stress showed that response speed and efficiency of roots were higher than that of leaves, so was178than9782. This might be one of reasons178had higher resistance to lead stress than9782.5. Combining previous research results, two possible antiretroviral ways could be speculated. One way was that regulation via miRNA may be the reason maize showed resistance to lead stress. By regulating transcription factors involved in signal transduction and resistance pathway, these miRNA could regulate corresponding metabolic passways, which endowed resistance for maize. The other way was that the different expression levels of miRNA were the results of up-stream biological processes against lead stress. On adverse situation, maize would activate a series of metabolic passways to resist the stress, and in the process, the expression levels of proteins and transcription factors related to the biosynthesis of mature miRNA and expressional regulation changed, which influced expressions of some specific miRNA. These miRNA then affected the expression levels and activities of their target genes, which endowed maize particular resistance. |
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