Effects Of Pti Gene On Tomato Disease Resistance And Fruit Quality

The study of plant disease resistance genes and their mechanisms has been a hot topic in plant functional gene analysis and genetic improvement.Tomato(Solanum lycopersicum),a widely grown economic fruit-vegetable crop,is also a model for fruit development,nutritional quality,and bacterial disease investigation.Pto(P.s.pv.tomato),encoding a serine/threonine kinase,is a tomato resistance gene obtained by map-based cloning.Pto plays a key role in tomato resistance by recognizing and binding the effector protein,which injected into plant cells by pathogenic bacteria,and thus triggering the downstream defense response.Pto interacts with three transcription factors in yeast two hybrid system.They are named Pto interaction protein(Pti),that is,Pti4,Pti5 and Pti6.Pti are reported as downstream genes of Pto pathway by promoting the expression of pathogenesis-related genes.Moreover,the Pti encoding proteins are homologous with tobacco ethylene reactive element binding protein.Ethylene,as a plant hormone,can promote fruit ripening and involve in multiple regulation processes in plants,including immune responses to disease.However,there are few reports on Pti genes in recent years,and the effect on tomato plant resistance and fruit quality needs to be further determined.In the present work,Pti6-overexpression vector was constructed for Agrobacterium-mediated genetic transformation in tomato.The quantitative PCR showed significantly increased expression of Pti6 in transformed plants.After inoculated with pathogenous Pst {Pseudomonas syringae pv.tomato),Pti6 overexpressed lines indicated remarkably reduced leaf lesions and colony counts of pathogenetic bacteria compared with wild-type plants.Furthermore,the activities of phenylalnine ammonialyase(PAL),catalase(CAT)and peroxidase(POD)in transformed plants showed significantly higher level than those in wild-type tomato fruits.Accordingly,the content of malondialdehyde(MDA)decreased,suggesting that Pti6 plays a role in improving tomato defense response.In addition,ratio of length to width,hardness,weight,soluble solid content,acidity and lycopene content in Pri4,Pti5 and Pti6-overexpression tomato fruits were measured.The results indicated that Pti genes had no significant effect on fruit characters when improving the resistance to disease.Previous studies have shown that many transcription factors interact with other proteins for fine regulation of plant life activity.The interaction protein of Pti has not been reported except for Pto.In this work,the yeast two-hybrid library was constructed from tomato roots,leaves,flowers and fhuits(including immature green,mature green,breaker,breaker after 10 days,four different stages).The detection displayed that the average inserted fragment was more than 1200 bp,and the total library capacity was about 1.05 ×107 CFU.By constructing yeast two-hybrid vectors of Pti genes and determining their self-activating,Pti4 was selected for library screening.Based on the plasmid sequencing of positive yeast clones,six putative interaction transcription factors(ripening regulated protein DDTFR8,REF/SRPP-like protein,U-box domain-containing protein,zinc finger protein ZAT5-like,GAGA-binding transcriptional activator and proline-rich protein 4-like)were indicated.In view of the similarity of Pti genes1 function,the information of interaction proteins obtained in this work will provide a basis for the elucidation of their mechanism.