中科院遺傳與發(fā)育生物學(xué)研究所謝旗實驗室采用反向遺傳學(xué)策略，結(jié)合分子生物學(xué)和生物化學(xué)等方法，發(fā)現(xiàn)雙生病毒甜菜嚴重曲頂病毒（Beet Severe Curly Top Virus, BSCTV）能夠通過編碼的C2蛋白與植物宿主蛋白腺苷甲硫氨酸脫羧酶1（S-adenosyl-methionine decarboxylase 1，SAMDC1）相互作用，并抑制26S蛋白酶體介導(dǎo)的SAMDC1蛋白降解。功能研究發(fā)現(xiàn)，C2蛋白對植物宿主蛋白SAMDC1的這一正調(diào)控過程能夠影響植物宿主對自身基因以及病毒基因組的從頭甲基化過程，進而影響植物宿主基因沉默介導(dǎo)的抗病毒防御反應(yīng)和病毒DNA在植物宿主中的積累。
Plant viruses are excellent tools for studying microbial–plant interactions as well as the complexities of host activities. Our study focuses on the role of C2 encoded by Beet severe curly top virus (BSCTV) in the virus–plant interaction. Using BSCTV C2 as bait in a yeast two-hybrid screen, a C2-interacting protein, S-adenosyl-methionine decarboxylase 1 (SAMDC1), was identified from an Arabidopsis thaliana cDNA library. The interaction was confirmed by an in vitro pull-down assay and a firefly luciferase complemention imaging assay in planta. Biochemical analysis further showed that the degradation of the SAMDC1 protein was inhibited by MG132, a 26S proteasome inhibitor, and that C2 could attenuate the degradation of the SAMDC1 protein. Genetic analysis showed that loss of function of SAMDC1 resulted in reduced susceptibility to BSCTV infection and reduced viral DNA accumulation, similar to the effect of BSCTV C2 deficiency. Bisulfite sequencing analysis further showed that C2 deficiency caused enhanced DNA methylation of the viral genome in infected plants. We also showed that C2 can suppress de novo methylation in the FWA transgenic assay in the C2 transgene background. Overexpression of SAMDC1 can mimic the suppressive activity of C2 against green fluorescent protein–directed silencing. These results suggest that C2 interferes with the host defense mechanism of DNA methylation-mediated gene silencing by attenuating the 26S proteasome-mediated degradation of SAMDC1.
