Type ? Accessory Protein HrpE Mediates An Effector Translocation From Rice Bacterial Blight Pathogen And Induces The Plant Immunity And Growth

Xanthomonas oryzaepv.oryzae(Xoo)is a devastating pathogen that infects the rice crop and causes significant yield loss.The pathogen deploys its Type ? secretion system to secrete the effectors and toxic proteins from its body to the cytosol of the plant.Xoo is known to inject the effectors proteins and other toxins by using a specialized structure called as pilus.HrpE is the major constituent of the hrp pilus.The aim of this study was to elucidate the importance of HrpE in Type ? secretion system(T3SS)and effect of deletion of HrpE on growth and physiological functions of the bacteria.Moreover,our study shed the light on the importance of HrpE protein produced by prokaryotic expression when applied to the plants have potential to induce the immune response and promote the plant growth.Firstly,we explicate the importance of pilus in type ? secretion system.Many species of plant-pathogenic gram-negative bacteria translocate virulence or avirulence proteins by type ? secretion system using pilus pathway.HrpE is the fundamental component of pilus and is required for the translocation of protein effectors to the cytosol of the plant cell.Here,we show that hrpE gene can execute various physiological and pathological functions besides effectors secretion.Any genetic disruption or mutation in genome of pathogen results in aggravation of normal functioning affecting the bacterial motility leading to decreased growth.The hrpE deletion halts the translocation of transcription activator-like(TAL)effector pthXol;adversely affecting the pathogen virulence.This indicates that deletion of hrpE could affect the pathogenicity and disease severity.Later,we analyzed the role of HrpE protein in elicitation of the defense response.When HrpE protein produced by prokaryotic expression is applied to plants,the recombinant protein is highly effective at inducing the defense response.The purified HrpE protein induces various defense responses like callose deposition and H2O2 accumulation.Pretreatment of HrpE in plants challenged with the pathogen resulted in reduced growth of pathogen itself.There was a significant increase in the transcriptional regulation of genes involved in plant defense signaling and induced systemic resistance upon pre-treatment of hrpE protein as compared to plants challenged with only Xoo or RFP treated controls.Moreover,leaf photosynthesis efficiency is enhanced in HrpE-treated plants.These results provide experimental avenues to modulate the plant defense and growth trade-off by manipulating a bacterial T3 accessory protein.The gram negative bacteria are known to produce the harpin proteins which can enhance the plant growth.The growth enhancing potential of the harpins are beneficial and may be associated with the functional regions of the proteins.Harpins are also known to stimulate the hypersensitive cell death(HCD)but identification of functional terminal of the proteins may be beneficial to use the deleterious regions of these proteins without any negative effects like HCD.Here,we report the identification and testing of the derivate fragments of HrpE protein from Xanthomonas oryzae pv.oryzae,the pathogen that causes the bacterial blight disease in rice.Two fragments of the HrpE protein i.e.C-HrpE and N-HrpE generated by polymerase chain reaction-based mutagenesis are evaluated for their response on the seed vigor index and vegetative growth of the rice plants.Rice seedlings and plants evaluated for their root and shoot morphology showed that N-HrpE protein is essential for plant growth enhancement and increased photosynthetic efficiency.Rice plants grown under the influence of HrpE and its derivate fragments were evaluated for the transcriptional profiling of the genes related to the plant growth and quantification of the growth regulatory enzymes by UPLC provides the necessary avenues to prove that HrpE requires N terminus to enhance the vegetative growth in rice.