Transcript Analysis Of Wheat FHB-resistance Near-Isogenic Lines Induced By Fusarium Graminearum And The Cloning Of Resistant-Related Gene

Fusarium head blight (FHB) disease, which is caused by Fusarium graminearumSchwabe, is a devastating disease of wheat worldwide. In addition to the decrease in grainyield, FHB can also lower grain quality by producing mycotoxins, which are detrimental toboth humans and animals. Currently, the molecular mechanisms involved in resistance againstF. graminearum are still not very clear. After the observation of different stages of diseaseprogression on F. graminearum inoculated spikes by scanning electron microscopy, wepresented systems analysis of FHB near-isogenic lines Apogee73S2(resistant) and Apogee(susceptible) at the transcriptomic levels during F. graminearum infection. Genome-widegene expression profiling was conducted by solexa sequencing. NPR1gene plays a key role insystemic acquired resistance (SAR) and provides broad-spectrum resistance in Arabidopsis.Based on the analysis of the gene expression profiling, three NPR1-like genes were clonedfrom Apogee73S2induced by F. graminearum using RT-PCR, which were designated asTaNPR1, TaNPR2, and TaNPR3. The main results were as follows:1. During the early stage of infection, most hyphae of F. graminearum did not penetratethe host immediately but just elongated and branched on the inner surface of lemma, so wedid not observe disease spots before24h. After24h, infection went into a main penetrationstage. A large number of infection hypha arose from the runner hyphal and hyphal networkquickly formed. We are surprised to find the formation of multiple secondary hyphalstructures during this stage. Infection hypha can not only directly invaded into the epidermalcell wall, but also spread under the cuticular layer. A symptom of brown spots was apparenton the host tissues at36h, and was more visible at72h.2. Compared with control,2743up-regulated and3793down-regulated genes weredetected in Apogee73S2after inoculation with F. graminearum. While, only2042 up-regulated and2049down-regulated genes were found in the susceptible line Apogee.Several respects of metabolic process during F. graminearum infection were changedobviously. Genes participating in glycolysis and TCA cycle were up-regulated. On thecontrary, the transcript abundance associated with photosynthesis and electron transport wassignificantly reduced. Notably, a variety of genes involved in defensive, detoxication,transport, oxidative burst, signal transduction, and secondary metabolism were significantlyinduced.3. Subsequently, the expression patterns of twenty six genes induced by F. graminearumwere assessed by quantitative real-time PCR on an inoculation time-course of Apogee73S2and Apogee. Interestingly, genes associated with lignin biosynthesis, SA and JA signalingpathway, and biotic stress were activated to defense against F. graminearum invasion, andsome of genes were more induced in Apogee73S2than in Apogee. Furthermore, it was foundthat an alternative oxidase (AOX) and UDP-glucosyltransferase only expressed in resistantline Apogee73S2were obviously up-regulated after F. graminearum infection. These specificgenes may make great contribution to resistance against F. graminearum.4. The open reading frames of the three genes encode580,607, and601amino acidresidues, respectively. The three wheat NPR1-like proteins have the conversed BTB/POZ,ANK and NPR1_like_C domain as well as the conversed amino acid residues with importantfunction. However, only TaNPR1has the two conversed cysteine residues that are essentialfor the NPR1oligomer formation. Phylogenetic analysis showed that TaNPR1was involvedin the NPR1protein groups, while TaNPR2and TaNPR3were close to NPR1homologues.Quantitative RT-PCR assay revealed that the three NPR1-like genes can be induced bydefense related signal molecules, such as salicylic acid and methyl jasmonate. TaNPR1andTaNPR3were induced earlier and up-regulated more significantly in response to F.graminearum infection in the resistant line Apogee73S2than in the susceptible line Apogee.However, the transcription of TaNPR2was not obviously changed either in the resistant orsusceptible near-isogenic lines after inoculation with F. graminearum. These results suggestthat TaNPR1and TaNPR3may be involved in the defense response to F. graminearum.