Comparison Of Gene Expression Profiles Between Potato (Solanum Tuberosum L.) Horizontal Resistance And β-Aminobutyric Acid Induced Resistance Against Phytophthora Infestans

The year 2008 has been declared the International Year of the Potato by the United Nations,noting that potato,as the fourth largest crop species,can play vital roles in facing food security and eradicating poverty.Potato late blight,caused by Phytophthora infestans(Mont.) de Bary,ranks the most destructive disease in world agriculture,has seriously limited the potato production and development.Current disease control in the field depends on repeated application of large amounts of fungicides.However,this strategy resulted in environmental problems,pesticide residue and evolution of new races of P.infestans with new virulence alleles.Triggering the host plant's defense system to defend itself against pathogen attack seems to be quite prospective.Since the major gene resistance is easy to be overcome by new isolates of P.infestans in potato,horizontal resistance become "a great value" due to its durable and stable performance.In addition, plants also employ inducible resistance mechanisms which can be triggered by a variety of biotic and abiotic stimuli.A non-protein amino acid DL-β-amino-butyric acid(BABA) is capable of protecting numerous plant species against various pathogens.Moreover, BABA-induced resistance(BABA-IR) possesses a feature like the horizontal resistamce which is also durable and stable.However,to date,we know little about the molecular processes of horizontal resistance and BABA-IR,which greatly limits the in-depth study of the resistance mechanism and full use of the resistant resources.In this study,we compares gene expression profiles of a potato clone harboring horizontal resistance to P. infestans in response to BABA and the pathogen by using cDNA-AFLP,aiming at foundational elucidation of molecular mechanisms of BABA-IR and horizontal resistance. The main results are as follows:1."R-gene-free" potato plants were sprayed with BABA at concentration of 0.5mmol/L, 1mmo/L,2mmol/L and 4mmo/L.After 1d,2d,3d and 4d,the leaves were detached and inoculated with P.infestans.The results indicated that potato plants pre-treated with 2mmol/L or 4mmo/L BABA exhibited a significantly higher level resistance to P. infestans compared to the control.2.In total,101 transcript derived fragments(TDFs) showed significant differential expression among the BABA treated samples,P.infestans inoculation and their respective control ones.About half of differentially expressed fragments(49) were overlapped in both BABA and P.infestans induction systems indicating BABA,to a large exrend,induces plant resistence through activating the plant denfence system.Most of the TDFs in common expressed earlier in response to BABA than in response to the pathogen implying early activation of the plant defence system is a main mechanism of BABA-IR. Homology analysis showed that these TDFs involved in signalling,cell wall strengthening and synthesis of antimicrobial compounds.Two TDFs were verified to play important roles in tobacco induced resistance using vires-induced gene silencing,fuether approving the genes selected are involved in response to the pathogen attack.3.Several differentially expressed TDFs were similarities to genes involved in SA and JA dependent signal pathways,indicating that the two signal pathways play roles in BABA-IR.These TDFs related to signaling were also up-regulated by P.infestans, demonstrating that the signal pathway controlling pathogen induced could be triggered by BABA,and implying the extent crosstalk between BABA-IR and horizontal resistance.4.The CDS sequence of gene StWRKY5 was cloned using the method of combination with Silico cloning and 3'-RACE.GenBank accession number is EU056917.The gene contains 339 bp 3'-UTR region and the peptide sequence was predicted to be 297 amino acids.The deduced StWRKY5 protein would be WRKY transcription factor due to it contains conserved WRKYGQK motif and C2H2 zinc finger motif.Southern blot showed potato genomes possess 1-2 copies of StWRKY5.Semi-quantitative RT-PCR analysis showed that StWRKY5 were induced at 4 h by P.infestans,BABA and SA,while it expressed at 12 h and 24 h after MJA and wound,respectively.These efforts made the foundation to further study the function of StWRKY5.