Biochemical Characterization Of Small Heat Shock Proteins And Their Role In Plant Viral Infection

The small heat shock protein(sHSP)is a kind of molecular chaperone proteins,which not only protect the body from stress damage,but also play an important role in protein folding,intracellular transport,degradation and signal transduction pathways.In the previous study,we cloned a sHSP gene from rice plant(OsHSP20).The OsHSP20 can interact with RNA-dependent RNA polymerase(RDRP)of Rice stripe vrus(RSV)and form homologous oligomers or granular structures within the cytoplasm.However,its function still remains unclear.In order to further explore its function,its expression patterns in response to different abiotic stresses were firstly investigated by qRT-PCR.The gene was found to be significantly induced by heat and salt stress,but not affected by drought treatment.Subsequently,we found that heterologous expression of OsHSP20 could significantly enhance the tolerance of E.coli and yeast cells to heat and salt stress.Its recombinant proteins were purified from prokaryotic cells and shown to have molecular chaperone activity in vitro in biochemical assays.To determine the relationship among its self-interaction,chaperone activity and stress resistance,five truncated mutants were constructed for further analysis.The results showed that the self-interaction,chaperone activity and stress resistance of OsHSP20 were closely related to its N-terminal and α-crystallin domain(ACD)domains,indicating that the protein may exert its physiological and biochemical functions by self-interaction.To further explore the functional properties of this kind of sHSP in plants,OsHSP20 and its homolog NbHSP20 were transformed into rice(Oryza sativa)and N.benthamiana by Agrobacterium-mediated method,respectively.After treating the transgenic rice plants with stress,the overexpression of OsHSP20 effectively alleviated the damage of rice seed activity under heat stress,but also promoted seed germination and seedling growth and development,as well as reduced the inhibition of root growth by salt stress,indicating that the overexpression of OsHSP20 increased the tolerance to heat and salt stresses.On the other hand,the transgenic N.benthamiana plants were artificially inoculated with tomato mosaic virus(ToMV),Turnip Mosaic Virus(TuMV)and RSV,and were found to delay the symptom development,indicating that NbHSP20 may positively regulate the defense response of N.benthamiana to diseases.These results will be helpful to elucidate the role of sHSP in plant stress response and provide a basis for further study on the biological function of sHSP during virus infection in plants.