Transcriptome Analysis Of Rosa Odorata Var.Gigantea And R.Longicuspis Var.Longicuspis Responding To Podosphaera Pannosa Infection And Mining Of MLO Unigenes

Powdery mildew disease caused by powdery mildew pathogen,Podosphaera pannosa,is the largest disease in the global cut rose production.It is also one of the major diseases of garden rose and pot rose.At present,repeated application of chemical agents is the main way to prevent and reduce the occurrence of the powdery mildew disease in rose industry,which not only increases the production costs,but also causes environmental pollution and destruction.Rosa odorata var.gigantea and R.longicuspis var.longicuspis are two wild rose species.R.gigantea is susceptible and the R.longicuspis is immune to powdery mildew.The MLO genes are members of a class of plant-specific gene family.The MLO proteins are located in the plasma membrane and have seven transmembrane domains and one C-terminal calmodulin-binding domain.The MLO genes have been extensively studied in some plant,including arabidopsis,rice,barley,and wheat.However,few studies have been reported in rose.At present,domestic and foreign studies in powdery mildew of rose mainly focus on histopathology,physiology and biochemistry.Therefore,exploring the rose-powdery mildew pathogen interaction mechanism and mining of MLO genes of resistant to powdery mildew,is of great significance to rose molecular breeding for resistance to disease.In this study,we used RNA-seq technology and bioinformatics methods to analyze the transcriptome and to mine the resistance to powdery mildew MLO unigenes of young leaves of R.gigantea and R.longicuspis at 0 h,6 h and 12 h after infection with powdery mildew pathogen.The main findings were as follows:1.A total of 59725 and 62281 unigenes were obtained from the transcriptome data of R.gigantea and R.longicuspis,respectively.Among which 31545 and 32133 unigenes were annotated to in the four major databases respectively.We obtained 40(including 38 up-regulated and 2 down-regulated genes)and 2864(including 1928up-regulated and 936 down-regulated genes)DEGs in the 6 h and 12 h of R.gigantea after infection with powdery mildew pathogen,respectively;211(including 159up-regulated and 52 down-regulated genes)and 37(including 28 up-regulated and 9down-regulated genes)DEGs in the 6 h and 12 h of R.longicuspis after infection with powdery mildew pathogen,respectively.2.The results of KEGG pathway enrichment analysis showed that the molecular responding mechanism to powdery mildew pathogen infection of R.gigantea and R.longicuspis were regulated not by single gene but by multigene network.However,R.gigantea and R.longicuspis responded to the infection differently.With a more complex and diverse regulation network,R.gigantea responded slower than R.longicuspis.3.Based on the transcriptome sequencing of the R.gigantea and R.longicuspis,23 MLO unigenes were identified and analyzed by using bioinformatics methods.By comparing with other species homologous genes,we confirmed that six candidate MLO unigenes were associated with powdery mildew resistance,and only two(RgMLO6 and RlMLO7)of them resembled the typical structures of MLO powdery mildew resistant genes according to the results of conserved motifs analysis.4.The results of qRT-PCR showed that the above six candidate MLO unigenes were differently regulated by infection of powdery mildew pathogen.The relative expression of RgMLO6 and RlMLO7 unigenes was positively up-regulated.