Transcriptional Analysis of Maize Resistance against Fusarium graminearum

Abstract

Gibberella stalk rot, caused by Fusarium graminearum (teleomorph, Gibberella zeae), is one of the most devastating soil-borne diseases in maize. It seriously decreases maize yield and quality. Molecular mapping led to the identification of two QTLs, qRfg1 and qRfg2, on chromosomes 10 and 1 respectively, conferring resistance to Gibberella stalk rot. In order to characterize the defense mechanism of maize against F. graminearum, NIL-R with resistant alleles at both QTLs and NIL-S with the susceptible alleles at both QTLs were generated and used in transcriptome analysis. After inoculation of young seedling roots of both NILs with the F. graminearum spores, the inoculated roots were sampled at 0, 6, and 18 hours after inoculation (hai) for transcriptome analysis using RNAseq. The basal difference was achieved by the comparison between control samples. In total, 2958 genes were differentially expressed between control samples of NIL-R and NIL-S, among which 1170 genes were more abundant in NIL-R. GO analysis revealed that genes involved in biological processes related to JA/ET and SA biosynthesis, JA/ET mediated signaling pathway and SA mediated signaling pathway were significantly enriched. Phenylpropanoid biosynthesis process was enriched in the genes more abundant in NIL-R and genes encoding enzymes involved in phenylpropanoid biosynthesis like PAL, 4CL2, CAD, and HCT were more abundant in NIL-R. There were 431 genes differentially expressed between NIL-R and NIL-S at 6 hai, among which 83 genes were more abundant in NIL-R. Genes encoding pathogenesis-related (PR) proteins like lipid-transfer protein and germin-like protein were more abundant in NIL-R. Among the 1292 genes differentially expressed between NIL-R and NIL-S. At 18 hai, 291 genes were more abundant in NIL-R. Genes involved in ET biosynthesis like ACO and JA biosynthesis like LOX were more abundant in NIL-R. Genes involved in DON detoxification like PDR1 and MDR2 were more abundant in NIL-R. After inoculation with F. graminearum, 428 genes were exclusively up-regulated in NIL-R at 6 hai compared with control. Genes involved in ET biosynthesis and ET-mediated signaling pathway like ACO, ERF, EBF1, and EIL1 and pathogenesis-related genes like PR1, OSM34, and germin-like protein were exclusively up-regulated in NIL-R. At 18 hai, 359 genes were exclusively up-regulated in NIL-R compared with control. Pathogenesis-related genes like PR1, PR4, and genes encoding 第 8期 刘永杰等: 玉米抗禾谷镰刀菌的转录组分析 1123 the transporters of DON out of cytoplasm like ABC transport family protein, heavy metal transport protein and MATE efflux family protein were exclusively up-regulated in NIL-R. All these results indicate that NIL-R can increase the resistance of maize to F. graminearum by the constitutive resistance characterized by the higher expression of genes related to defense responses. Genes involved in defense responses exclusively up-regulated in NIL-R and higher expression level of disease resistance genes in NIL-R at 6 and 18 hai may restrict the pathogen invasion after infection. The phenylpropanoid biosynthesis pathway and DON-detoxification proteins identified in this study are important for the resistance against F. graminearum infection.