Microscopic and Transcriptomic Comparison of Powdery Mildew Resistance in the Progenies of Brassica carinata × B. napus .

Powdery mildew is a widespread disease in rapeseed due to a lack of resistant germplasm. We compared the foliar epidermal features and transcriptomic responses between the resistant (R) and susceptible (S) plants among the two parents and progenies of Brassica carinata × B. napus . The amount of cuticular wax and callose deposition on the R plants was much lower than that on the S plants; hence, these chemicals are not all essential to pre-penetration resistance, although the cuticular wax on the R plants had more needle-like crystals. A total of 1049 genes involved in various defense responses were expressed differentially among the R/S plants. The expression levels of two well-known susceptibility genes, MLO6 and MLO12 , were much lower in the R plant, indicating an important role in PM resistance. A set of genes related to wax biosynthesis ( KCS6 , LACS2 , CER and MAH1 ), cell wall modification ( PMR5 , PMEI9 , RWA2 , PDCB1 and C/VIF2 ), chloroplast function ( Chlorophyllase-1 , OEP161 , PSBO1 , CP29B and CSP41b ), receptor kinase activity ( ERECTA , BAK1 , BAM2 , LY M1 , LYM3 , RLK902 , RLP11 , ERL1 and ERL2 ), IPCS2 , GF14 lambda , RPS4 and RPS6 were highly expressed in the R plants. In the S plants, most highly expressed genes were involved in later defense responses, including CERK1 , LYK4 , LIK1 , NIMIN-1 , CHITINASE 10 , PECTINESTERASE , CYP81F2 and RBOHF and the genes involved in salicylic acid-dependent systemic acquired resistance and hypersensitive responses, indicating the occurrence of severe fungal infection. The results indicate that some uncertain pre-penetration defenses are pivotal for high resistance, while post-penetration defenses are more important for the S plant survival.