CaPti1 As A Positive Regulator Involves In Plant Immune Defense And Salt Stress

Pti1,a protein interacting with resistance(R)protein Pto,has been found to be involved in plant response to pathogens attack as well as abiotic stresses,but the underlying mechanism is not fully understood.In this study,CaPtil encoding a protein of 354 amino acids was isolated from the cDNA library of Capsicum annuum.Its up-stream promoter was also cloned that contains many potential cis-elements response to disease and abiotic stresses,suggesting CaPtil might involve in the signaling of plant diseases resistance and abiotic stress response.Typical HR mimicking cell death was found to be triggered in pepper leaves by transient expression of CaPtil,which is accompanied with up-regulation of SA response genes and down-regulation of JA response genes.Meanwhile,over-expression of CaPtil in tobacco enhanced resistance against Ralstonia solanacearum inoculation and increased tolerance of tobacco to salt stress.A protein called CaCSN5,interacting with CaPtil,was screened by Yeast Two-hybrid.Previous studies show CSN5,a subunit of COP9 signalosome(CSN),serves as activator for JA synthesis in Solanum lycopersicum.CaCSN5 was also found to trigger HR mimicking cell death by transient expression in pepper leaves,but the HR mimicking cell death was compromised when CaCSN5 was expressed together with CaPtil.In addition,our data show that membrane localization of CaPti1 is necessary for cell death-mediated defense signaling;studies indicate free CSN5 is found in nucleus and cytoplasm,while CSN5 perform its biological function predominantly in cell nucleus;the interaction of CaPtil with CaCSN5 may influence the subcellular localization of the two proteins,which results in the compromised HR mimicking cell death.These data suggest that CaPti1 is a positive factor in pepper resistance to pathogenic invasion and salt treatment,which may be regulated by SA but not JA signaling pathway,the function of CaPti1 can be modified by CaCSN5,but the underlying mechanism remain further investigation.