QTL-specific microarray gene expression analysis of wheat resistance to Fusarium head blight in Sumai-3 and two susceptible NILs.

Fusarium head blight, predominantly caused by Fusarium graminearum (Schwabe) in North America, is a destructive disease that poses a serious threat to wheat (Triticum aestivum L.) production around the world. cDNA microarrays consisting of wheat ESTs derived from a wheat - F. graminearum interaction suppressive subtractive hybridization library were used to investigate QTL-specific differential gene expression between the resistant Chinese cultivar Sumai-3 and two susceptible near isogenic lines (NILs) following inoculation with F. graminearum. Stringent conditions were employed to reduce the false discovery rate. A total of 25 wheat unigenes were found to express differentially in response to F. graminearum infection. Genes encoding pathogenesis-related (PR) proteins such as beta-1,3-glucanase (PR-2), wheatwins (PR-4), and thaumatin-like proteins (PR-5) showed a significant upregulation in genotypes having the Sumai-3 3BS region. For these three genes, the gene activity was significantly less in the genotype (NIL-3) lacking the Sumai-3 3BS segment. Significant upregulation of phenylalanine ammonia-lyase was detected only in the resistant Sumai-3, indicating the importance of both the 2AL and 3BS regions in the activation of effective defense responses to infection by F. graminearum. Differences in gene expression between the resistant Sumai-3 and the susceptible NILs were found to be mainly quantitative in nature.

Microarray analysis of Fusarium graminearum-induced wheat genes: identification of organ-specific and differentially expressed genes.

A wheat cDNA microarray consisting of 5739 expressed sequence tags (ESTs) was used to investigate the transcriptome patterns of the glume, lemma, palea, anther, ovary and rachis dissected from infected wheat spikes after inoculation with the fungus Fusarium graminearum, the causal agent of fusarium head blight (FHB) disease. Stringent conditions were employed to reduce the false discovery rate. The significance analysis of microarrays (SAM) was used to identify transcripts that showed a differential response between fungal-challenged vs. control plants. To verify the microarray data, Northern blot analysis was carried out on randomly selected up-regulated clones. We observed 185 (3.2%) up-regulated and 16 (0.28%) down-regulated ESTs in the six organs constituting the wheat spike. Many up-regulated ESTs (46.67%) showed no homology with sequences of known functions, whereas others showed homology with genes involved in defence and stress responses, the oxidative burst of H(2)O(2), regulatory functions, protein synthesis and the phenylpropanoid pathway. The monitoring of genes in specific organs avoided the averaging of expression values over multiple organs that occurs when using data from the whole spike. Our data allowed us to uncover new up-regulated genes expressed in specific organs. The study revealed that each organ had a defined and distinctive transcriptome pattern in response to F. graminearum infection.