Study On The Mechanism Of Cross Protective Effect Of Potato Virus Y

Potato virus Y（PVY）is one of the main viruses that restrict potato production.In recent years,with the increase in the incidence of PVY in potato production areas,more and more recombinant strains have been discovered,and their genome structures are very similar.However,the pathogenicity is quite different.The simultaneous existence of multiple PVY strains has aroused widespread concern.In this study,different popular PVY strains in Heilongjiang Province were used to study the cross protection of PVY on potato.The two isolates of PVY^N-Wiand PVY^NTN-NW（SYR II）,which are widely present in Heilongjiang producing areas,were selected as the source material of the virus,through the analysis of the virus sequence,the identification of biological symptoms,and real-time fluorescent quantitative PCR（q PCR）detection technology,transcriptome and proteomics sequencing,etc.carry out relevant tests on samples,and observe the effects of experimental treatments on potatoes.The specific results are as follows:1.The isolate HLJ-BDH-2（kx032614,hereinafter referred to as BDH）of PVY^N-Wi strain with weak pathogenicity was selected to infect potato for 15 days,and then challenged to inoculate the isolate INM-W-369-12（kx688601,hereinafter referred to as 369）of PVY^NTN-NW（SYR II）strain with strong pathogenicity.After inoculation,it was compared with the two strains infecting potato alone.After comparison and observation,it is found that BDH alone infects potatoes with light flower leaves or even no symptoms,369 infects potatoes with heavy flower leaves,leaf shrinkage,deformity and stem necrosis.When BDH and 369 infect potatoes successively,the symptoms are basically the same as those of BDH alone,it is speculated that there is cross protection between PVY weak strain BDH and strong strain 369.After successful virus inoculation,q PCR detection showed that the two strains infected potato alone,and the cumulative concentration of virus in the host was very high.However,in the plants inoculated with strong virus 15 days after weak virus inoculation,the strong virus was always at a low concentration.It is speculated that the concentration of strong toxin is inhibited due to the existence of weak toxin.2.In order to verify the diversity of cross protection,the effects of different seedling stages,different virulent strains,different potato varieties,different inoculation methods and different kinds of viruses on cross protection were measured.The results showed that there was cross protection in potato seedling stage and mature stage;Other virulent strains(PVY^NTN-NW-SYR-II-SC-1-1-2,KX688602;PVYN:O-HLJ-30-2,KX688599)were selected for challenge inoculation,and there was still cross protection;The protective effects of different varieties were slightly different due to different resistance,but the stability of cross protective effects was also proved in 8 varieties,such as Kexin 25,Eugene,Zaodabai,Atlantic,Longshu7,Qingshu 9,Lishu 6 and jizhangshu 12;The content of virus in rootstock was determined by grafting inoculation and compared with that detected after friction inoculation;The cross protection between different viruses was not obvious.Field experiments showed that the use of mild PVY^N-Wi strain could significantly protect potato from the infection of severely necrotic PVY^NTN-NW strain,which provided a possible solution for controlling the pvynin-nw necrotic strain causing ptnrd disease.3.The physiological indexes such as photosynthesis,peroxidase and related enzyme activities of ascorbic and glutathione acid systems at 12 h,24 h and 10 d after challenge inoculation were measured.It was found that the physiological characters after challenge inoculation were basically the same as those of BDH alone,and there were significant differences from those of 369 alone.4.The transcriptome and proteome sequencing of infected potato leaves were further carried out.Transcriptome sequencing found that the go entries with significant enrichment of differential genes on the 10th day after inoculation were mainly gene transcription and expression,especially the pathways related to protein translation.It is speculated that the weak virus can reproduce rapidly by using the host transcription and translation system.When the strong virus invades again,it has a competitive relationship with the weak virus,resulting in that the strong virus cannot replicate normally in the plant,so as to protect the host from the strong virus.The largest number of differential proteins obtained by proteomic KEGG analysis are ribosome,photosynthesis,oxidative phosphorylation,starch and sucrose metabolism,and carbon fixation of photosynthetic organisms.A total of 36 differential genes were obtained by transcriptome and proteome association analysis.The metabolic pathways involved in differential genes mainly include ribosome,amino sugar and nucleotide sugar metabolism,signal transduction and photosynthesis.5.The St SBT1.7 was screened by transcriptome and proteome analysis.To study the cross protection mechanism between PVY strains,the screened genes were constructed into overexpression and interference vectors,and then transferred into potato to analyze the function of genes.At the same time,the transient expression vector was constructed to analyze St SBT1.7.The results showed that St SBT1.7 was located in the plasma membrane and nucleus.The transgenic potato plants were obtained and the expression of salicylic acid related genes in the transgenic plants was measured.The results showed that the expression of salicylic acid related genes increased.After spraying SA,St SBT1.7 could respond to SA hormone,and the content of 369 in potato seedlings decreased.It is speculated that after the virus enters the plant,St SBT1.7 can respond to cross protective effects through salicylic acid pathway.