The present invention relates to a chemically modified
small interfering RNA (siRNA), and more particularly, to a chemically modified siRNA having enhanced
nuclease degradation resistance and effectively exhibiting RNAi activity compared to an unmodified siRNA in which 15 bases are extended at the 5'terminal of a
sense strand and the 15 bases are simultaneously subjected to phosphorothioate modification, i.e., a non-bridged
oxygen atom of a
phosphodiester bond is substituted with a
sulfur atom. The invention provides a siRNA delivery tool, a method for promoting siRNA delivery to cause
gene silencing and improving the efficiency of delivering siRNA to
plant cells and application of the siRNA delivery tool, siRNA modified by
thiophosphate can be effectively introduced into YFP (
Yellow Fluorescent Protein) transformed
arabidopsis thaliana leaves, and
gene silencing of YFP is realized. The invention also can effectively
silence endogenous genes of tobacco. Therefore, the
thiophosphate modified siRNA can be used for silencing a certain
gene of a
plant to achieve the effect of regulating good growth of the
plant or treating related plant diseases and
insect pests, and has potential agricultural production value and wide application prospect.