Function And Signaling Mechanisms Of Poly-galacturonase Inhibiting Protein In Plant Response To Disease Resistance

Polygalacturonase-inhibiting proteins(PGIPs)are plant proteins believed to play an important role in the defence against plant pathogen fungals.PGIPs specifically inhibit fungal PGs,which reduce the hydrolytic activity of polygalacturonases(PGs),limit the growth of plant pathogens,and also elicit defence responses in plant.In our paper,PGIP gene was cloned from Chorispora bungeana(Chorispora bungeana Fisch,et.Mey,Chorispora bungean)(CbPGIP1). Immunofluorescence localizes the spatial distribution.Quantitative real-time PCR and western blotting characterized CbPGIP1 expression profile in response to biotic and abiotic stresses.In addition,Nitric oxide(NO)has emerged as a key molecule involved in the interaction between plant and pathogens.In our paper,the signaling functions of ON in plant fungal pathogen stress and the regulation of AtPGIP1 was studied using Arabidopsis thaliana wild type and Atnos1 mutant plants.The results were showed as following:1.The cloned full-length CbPGIP1 cDNA from Chorispora bungeana was 1203 bp.The cDNA encoded a protein of 332 amino acids with a calculated molecular weight of about 36.9 KD and with an isoeleetric point(pI)of 6.93. Prediction of amino acid analysis shows that the full-length cDNA of CbPGIP1 contains tepical LRR(leucine-rich repeat)domain.The protein exhibits closest homology to a subgroup of AtPGIP1 and we thus refer to it as CbPGIP1.2.CbPGI1P-GFP fusion protein was expressed transiently in epidermal cells of onions by microprojectile bombardment.The result showed that the intracellular distribution of fusion protein was located in cytosol,indicating no specific cellular localization of CbPGIP1 to any cellular compartment.3.Quantitative real-time PCR and western blotting showed that Stemphylium solani,SA(salicylic acid)notably induced the CbPGIP1 gene expression,indicating that CbPGIP1 plays key role in plant disease resistance.4.The results of immunofluorescence suggested that the CbPGIP1 in leaf was evenly localized in all tissues but the CbPGIP1 in stem and root was mainly localized in the epidermis and vascular bundle.Further study suggests that CbPGIP1 has higher levels in leaves and stems than in roots.Perhaps such impediments of the spatial distribution can be major factors as host resistance that places severe restrictions on the host range for a pathogen.5.4℃,-4℃and NO all can induce the CbPGIP1 gene expression,surgesting that CbPGIP1 would play important role in abiotic stresses.Low temperature like other stresses can increase susceptibility to diseases,so cold induction of CbPGIP1 might provide protection from infections.In addition,NO induced the expression of CbPGIP1,indicating that NO may take part in CbPGIP1 expression in Chorispora bungeana.6.The results of immunofluorescence showed that the AtPGIP1 in leaf was evenly localized in all tissues but the AtPGIP1 in petiole,stem and root was mainly localized in the epidermis and vascular bundle.This is consistent with the result of Chorispora bungeana.Those results indicate that the spatial distribution of AtPGIP1 as a physical barrier against the attack of fungal pathogen. 7.NO increased the plant resistance to Stemphylium solani.Atnos1 mutant was homozygous mutant line with a T-DNA insertion in the first exon of Atnos1 gene.NOS activity in Atnos1 was about 25%of wild type under normal condition. Atnos1 was identified to have impaired NO production.Compared with wild type plants,Atnos1 mutant plants were more sensitive to disease stress.Treatment of Atnos1 mutant plants with SNP(a NO donor)decreased the sensitive to disease stress.There were not hypersensitive response-like lesions in Atnos1 mutant plants infected by Stemphylium solani SS31.The spread of Stemphylium solani was more quickly in Atnos1 mutant plants than wild type plants.In addition,NO can regulate the antioxidative enzymes in plant defence.Compared with wild type plants,the extent of SA and AtPGIP1 were both lower in the mutant infected by Stemphylium solani.In a word,as a singal molecular,NO plays an important role in plant diease resistance.In a word,the induction of PGIP by infection,low temperature,SA and NO indicates that PGIP has a role in defence of subnival plant Chorispora bungeana.In addition,NO is a signal molecule involed in the enhancement of disease resistance and regulation of AtPGIP1 expression.