Analysis Of The Interaction Between C4 Protein Encoded By Tomato Leaf Curl Yunnan Virus And NbSK?

Geminiviruses are a group of DNA viruses characterized by the unique twinned particles.Geminiviruses induce abnormal development and produce severe symptoms in plants,and are emerging as a major threat to agricultural production in China.We used C4 protein,the pathogenicity factor of Tomato leaf curl Yunnan virus(TLCYnV),to study the molecular mechanism of C4 pathogenicity and biological significance of the interaction between C4 and host factor(s).To identify he molecular mechanism of C4 pathogenicity,we screened a tobacco cDNA library using C4 as the bait.We found that NbSK? interacted with C4 and C4/NbSK?interaction determined C4-induced symptom development.Further,we silenced NbSK? in N.benthamiana using virus-induced gene silencing(VIGS)and transgenic RNAi technologies.NbSK? played an important role in symptom development.TLCYnV C4 could be phosphorylated by NbSK? in the nucleus,and C4 phosphorylation by NbSK? is essential for changed cellular distribution of NbSK? that is critical for symptom development.Phosphorylation of TLCYnV C4 by NbSK? promoted C4 myristoylation,and the myristoylation of phosphorylated C4 could interact with exportin-a(XPO I)to induce nuclear export of C4/NbSK? complex.Nucleocytoplasmic shuttling of C4 mediated by NbSK? is essential for its pathogenicity.Further study found that NbSK? interacted with D-type cyclin(NbCycDl;1)in the nucleus,and NbSK? could phosphorylate NbCycD1;1 to promote its degradation via 26S proteasome pathway.However,TLCYnV C4 directed NbSK? to the membrane and reduced nuclear accumulation level of NbSK?.The altered cellular distribution of NbSK? by C4 enhanced the stability of NbCycD1;1 which is favorable for making an environment suitable for geminivirus replication.Taken together,we identified the host factor-NbSK? that interacted with TLCYnV C4,and illuminated the molecular mechanism of C4 pathogenicity and biological significance of C4/NbSK? interaction.