玉米抗禾谷镰刀菌的转录组分析

Transcriptional Analysis of Maize Resistance against Fusarium graminearum

赤霉菌茎腐病是由禾谷镰刀菌(Fusarium graminearum,有性态,Gibberella zeae)引起的一类土传性病害,严重危害玉米的产量和品质。本研究依据玉米第10和第1染色体上的2个抗茎腐病QTL,q Rfg1和q Rfg2、培育近等基因系NIL-R(2个QTL位点均为抗病等位基因)和NIL-S(2个QTL位点均为感病等位基因)。在成株期和幼苗期接种禾谷镰刀菌,两近等基因系的抗性差异均显著。用2个近等基因系的幼根接种禾谷镰刀菌,进行转录组分析研究。结果表明,与NIL-S相比,NIL-R在接种禾谷镰刀菌后,乙烯(ethylene,ET)合成、信号途径基因,病程相关蛋白、脱氧雪腐镰刀菌烯醇毒素(deoxynivalenol,DON)解毒基因等呈现特异上调表达。与NIL-S相比,有1170个基因在NIL-R对照组中表达量较高,其中水杨酸(salicylic acid,SA)、茉莉酸(jasmonic acid,JA)和乙烯合成和信号介导途径以及苯丙烷合成途径中的基因显著富集;接种禾谷镰刀菌6 h或18 h后,病程相关蛋白、激素JA和ET合成基因、DON解毒基因在NIL-R中表达量较高。

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, q Rfg1 and q Rfg2, 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 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.