Molecular Mechanism Underlying The Interference Of Photosynthetic Rate By CP And HC-Pro Of Potato Virus Y

Viral infectioins always cause physiological alterations of the infected plants,such as chlorisis,decrease of photosynthetic rate and the change of chloroplast morphology.Viral infections have great influence on photosynthesis.Previous studies mainly focused on the determination of physiological parameters of virus-infected plants,while the molecular mechanism underlying these changes were seldom investigated.Potato virus Y(PVY)is an important plant virus.PVY coat protein(CP)and helper component proteinase(HC-Pro)were used as baits for the yeast two hybrid screening assay in our lab before,some chloroplast proteins were identified to interact with CP and HC-Pro respectively.Here,we focused on the CP/NtCF1? subunit interaction,the HC-Pro/NtCF1? subunit interaction and the HC-Pro/NtMinD interaction.The biological significance of the three interactions were discussed and the cause of the reduced photosynthetic rate of virus-infected plants was partially revealed.PVY CP was found to accumulate in the chloroplasts of virus-infected plants.The interaction between CP and the NtCF1? subunit was identified in yeast cells previously.Here,the GST pull-down assay was employed to confirm this interaction in vitro.To investigate the effect of CP on the reduction of photosynthetic rate,the transit peptide of Rubisco small subunit was fused to the N-terminus of CP protein to generate transgenic tobacco with CP accumulated in chloroplasts.Intact chloroplasts were isolated and the chloroplast proteins were used in the co-immunoprecipitation(Co-IP)assay.The results showed that CP and the NtCF1? subunit interacted in the chloroplasts.The chloroplast proteins were also extracted from PVY-infected tobacco and a Co-IP assay was conducted with the proteins.The results showed that CP co-precipitated with NtCF1? subunit in PVY-infected plants,indicating that the CP/NtCF1? subunit interaction really exists in natural infection.Meanwhile,the photosynthetic rate of CP transgenic plants was reduced by 28%compared to the wild-type plants.No effect of CP on the enzyme activity of ATP synthase in vitro was detected.However,the amount of ATP synthase was reduced by 30%in the CP transgenic plants.The photosynthetic rate of PVY-infected tobacco was reduced by 58%and the amount of ATP synthase was reduced by 43%.We assume that the interaction of CP and NtCF1? subunit might interfere with the assembly of ATP synthase whole enzyme,leading to a decreased amount of ATP synthase and finally caused the reduced photosynthetic rate in PVY-infected plants.HC-Pro employs a similar mechanism to interfere with photosynthetic rate.HC-Pro has no effect on the enzyme activity of ATP synthase,either.The interaction of HC-Pro and the NtCF1? subunit leads to a reduced amount of ATP synthase,and finally causes a decrease of photosynthetic rate.The CP/NtCF1? subunit and HC-Pro/NtCF1? subunit interactions together interfere with the energy base for photosynthesis,which is an important cause of the reduced photosynthetic rate in virus-infected plants.The interaction between HC-Pro and NtMinD was confirmed both in vitro and in vivo in our lab before.The biological significance of the HC-Pro/NtMinD interaction was further investigated here.HC-Pro was proved to inhibit the ATPase activity of NtMinD.Another important chloroplast division regulator NtMinE was cloned and the NtMinD/NtMinE interaction site was mapped to the C-terminus of NtMinD,which overlapped the interaction site of HC-Pro/NtMinD interaction.HC-Pro transgenic tobacco showed enlarged chloroplasts compared to wild-type plants.The interaction between HC-Pro and NtMinD affects the structure base of chloroplast,which is also a reason for the reduced photosynthetic rate in viral infected plants.