The Citrus tristeza virus (CTV) uses 3 silencing suppressor genes, p20, p23 and p25, to resist the attacks from its Citrus hosts. Inactivating these genes is therefore obviously a potential defensive option in additio...The Citrus tristeza virus (CTV) uses 3 silencing suppressor genes, p20, p23 and p25, to resist the attacks from its Citrus hosts. Inactivating these genes is therefore obviously a potential defensive option in addition to the current control strat-egies including aphid management and the use of mild strain cross protection. In this study, we cloned partial DNA frag-ments from the three genes, and used them to construct vectors for expressing hairpin RNAs (hpRNAs). To facilitate the formation of hpRNAs, the constructs were introduced in a loop structure. Fol owing transformation of sour orange (Citrus aurantium) with these constructs, 8 p20 hpRNA (hp20) and 1 p25 hpRNA (hp25) expressing lines were obtained. The 7 hp20 transgenic lines were further characterized. Their reactions to CTV were tested fol owing inoculation with CT14A and/or TR-L514, both of which are severe strains. Results showed that 3 lines (hp20-5, hp20-6 and hp20-8) were completely resistant to TR-L514 under greenhouse conditions for no detectable viral load was found in their leaves by PCR. However, they exhibited only partial suppression of TR-L514 under screen house conditions since the virus was detected in their leaves, though 2 months later compared to non-transgenic controls. Further tests showed that hp20-5 was tolerant also to CT14A under screen house conditions. The growth of hp20-5 was much better than others including the controls that were concurrently chal enged with CT14A. These results showed that expressing p20 hpRNA was sufifcient to confer sour orange with CTV resistance/tolerance.展开更多
Large-Eddy Simulation （LES） is applied to examine the turbulent mixing and evolution in a stably stratified flow with a thermally sharp interface. Turbulent velocity intensities and turbulent kinetic energy are anal...Large-Eddy Simulation （LES） is applied to examine the turbulent mixing and evolution in a stably stratified flow with a thermally sharp interface. Turbulent velocity intensities and turbulent kinetic energy are analyzed by considering the mean shear and stratification effects. The evolution of turbulent mixing layer and turbulent structures are mainly investigated. The results show that the streamwise intensities are much larger than the vertical intensities, and vertical fluctuations decay more rapidly at the presence of stratification. The qualitatively computational results suggest that the mixing layer, defined by the mean temperature, inclines to the side with small inlet velocity. The evolution of the half-width of the mixing layer shows two different slopes. The turbulent structure with high vorticity is restricted in the mixing layer especially in strong stratified cases.展开更多
The turbulent passive scalar fluxes were studied by separately considering the contributions of small eddy motions and large eddy ones. Explicit algebraic approximation was achieved for both small eddy and large e...The turbulent passive scalar fluxes were studied by separately considering the contributions of small eddy motions and large eddy ones. Explicit algebraic approximation was achieved for both small eddy and large eddy scalar fluxes. Especially, the large eddy scalar flux was modelled with complex diffusivity. The singular difficulties in usual algebraic scalar models, do not occur any more in this model. In addition, this new model provides a new way to reasonably describe the negative transport phenomena appearing in asymmetric turbulent flows.展开更多
基金supported by the International Science & Technology Cooperation Program of China (2012DFA30610)the National Natural Science Foundation of China (30571291)the Special Fund for Agro-Scientific Research in the Public Interest, China (201203075-07)
文摘The Citrus tristeza virus (CTV) uses 3 silencing suppressor genes, p20, p23 and p25, to resist the attacks from its Citrus hosts. Inactivating these genes is therefore obviously a potential defensive option in addition to the current control strat-egies including aphid management and the use of mild strain cross protection. In this study, we cloned partial DNA frag-ments from the three genes, and used them to construct vectors for expressing hairpin RNAs (hpRNAs). To facilitate the formation of hpRNAs, the constructs were introduced in a loop structure. Fol owing transformation of sour orange (Citrus aurantium) with these constructs, 8 p20 hpRNA (hp20) and 1 p25 hpRNA (hp25) expressing lines were obtained. The 7 hp20 transgenic lines were further characterized. Their reactions to CTV were tested fol owing inoculation with CT14A and/or TR-L514, both of which are severe strains. Results showed that 3 lines (hp20-5, hp20-6 and hp20-8) were completely resistant to TR-L514 under greenhouse conditions for no detectable viral load was found in their leaves by PCR. However, they exhibited only partial suppression of TR-L514 under screen house conditions since the virus was detected in their leaves, though 2 months later compared to non-transgenic controls. Further tests showed that hp20-5 was tolerant also to CT14A under screen house conditions. The growth of hp20-5 was much better than others including the controls that were concurrently chal enged with CT14A. These results showed that expressing p20 hpRNA was sufifcient to confer sour orange with CTV resistance/tolerance.
基金The project supported by National Natural Science Foundation of China under Grant No. 10272071, the Natural Science Foundation of Zhejiang Province under Grant No. Y604106, and the Key Academic Discipline of Zhejiang Province under Grant No. 200412.The authors are in debt to Prof. J.F. Zhang and Dr. W.H. Huang for their helpful suggestions and fruitful discussions.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10472063, 10742005)the Shanghai Pujiang Project for Talented Scholars(Grant No 06PJ14041)
文摘Large-Eddy Simulation （LES） is applied to examine the turbulent mixing and evolution in a stably stratified flow with a thermally sharp interface. Turbulent velocity intensities and turbulent kinetic energy are analyzed by considering the mean shear and stratification effects. The evolution of turbulent mixing layer and turbulent structures are mainly investigated. The results show that the streamwise intensities are much larger than the vertical intensities, and vertical fluctuations decay more rapidly at the presence of stratification. The qualitatively computational results suggest that the mixing layer, defined by the mean temperature, inclines to the side with small inlet velocity. The evolution of the half-width of the mixing layer shows two different slopes. The turbulent structure with high vorticity is restricted in the mixing layer especially in strong stratified cases.
基金The project supported by the National Natural Science Foundation of China(Grant No.1 9872042)
文摘The turbulent passive scalar fluxes were studied by separately considering the contributions of small eddy motions and large eddy ones. Explicit algebraic approximation was achieved for both small eddy and large eddy scalar fluxes. Especially, the large eddy scalar flux was modelled with complex diffusivity. The singular difficulties in usual algebraic scalar models, do not occur any more in this model. In addition, this new model provides a new way to reasonably describe the negative transport phenomena appearing in asymmetric turbulent flows.
