利用RNAi提高植物营养价值.pptVIP

Using RNAi to improve plant nutritional value Contents Introduction In 1998,Craig Mello and Andrew Fire found that traces of dsRNA(double-stranded RNA) in Caenorhabditis elegans（秀丽新小杆线虫） triggered a marked silencing of genes containing sequences identical to the dsRAN.They called this unconventional gene silencing RNA interference(RNAi).Some major human diseases,such as heart disease and cancer ,can be prevented by diatary supplements of specific nutrients.It can improve the nutritional value of plants for human and animal nurtition through RNAi. Mechanism 1. Small interfering RNA (siRNA) In 2000, Zamore etc.empirically showed that small RNAs of 21-23 nucleotides(核苷酸),named small interfering RNAs (siRNA),are the key factors in mediating specific RNA degradation in an in vitro Drosophila（果蝇） system.siRNAs were predicted and confirmed to be the direct products of dsRNA cleavage by the multidomain RNase Ⅲ enzyme Dicer(核酸内切酶). siRNAs are extremely similar in length to those discovered previously in virus-induced gene silencing(VIGS,病毒诱导的基因沉默)in plants ,and indeed Dicer activity is readily detected in wheat germ （小麦种子）and cauliflower extracts（花棷菜提取物）.siRNAs are subsequently assembled first into a multiprotein complex（多蛋白复合体） called an siRNP,and then into an active RNA-induced silencing complex(RISC,蛋白复合物);these complexes seek out and cleave target mRNAs that are complementary to the siRNA. 2.microRNA(miRNA)pathway An endogenous negative gene（消极的内源性基因） regulatory pathway, known as the microRNA(miRNA)pathway,also uses small RNAs of about 22 nucleotides.miRNAs are universally derived from a hairpinRNA（hpRNA，短发夹结构） with signifiant ,but imperfect,double-stranded character. Dicer is responsible for cleaing the miRNA precursor to produce the mature miRNA. Both siRNAs and miRNAs are thought to be assembled into similar RISC structures that regulate complementary RNA (cRNA) targets by targeting them either for cleavage or for translation repress