Fusarium head blight (FHB, also called head scab or scab) is a severe cereal disease that can lead to devastative yield loss and great reduction in grain quality. In addition, microtoxins produced by the necrotrophic pathogen in the infected grain, an important aggressiveness factor in blight, also can be a serious food health threat if the infected grains are consumed by people and livestock.  FHB is a complex disease. It can be caused by several Fusarium species with F. graminearum Schw. [teleomorph: Gibberella zeae (Schw.) Petch] as the major pathogen in East Asia, and North and South Americas. Airborne Fusaium ascospores landing on the spikelets of the host plants during anthesis under warm and humid conditions usually cause the disease. In spite of the intensive genetic and pathological researches of FHB, the mechanisms of pathogenicity, pathogenesis and host resistance largely remain unclear.  Adding to the difficulty is the fact that FHB resistance in wheat is mostly additive and quantitatively inherited. The goal of this proposed research is to develop a molecular understanding of Fusarium-wheat interaction during the FHB development. We are trying to identify the key steps during the pathogenesis so that we can develop a strategy for efficiently controlling FHB epidemics.  As the first step toward our goal, we have profiled gene expression during FHB pathogenesis with mRNA differential display, Affymetrix Wheat Genome GeneChip and real-time RT-PCR in several FHB-resistant and FHB-susceptible wheat cultivars/landraces.

Our preliminary data obtained with a modified mRNA differential display technique showed differential expression of genes during FHB development in both FHB-resistant and FHB-susceptible cultivars.  We will investigate these differentially expressed genes in FHB-resistant wheat cultivars at different stages of FHB development. After the expressed sequence tags (ESTs) of interest are identified, cloned, sequenced and characterized, we will clone the genes themselves and then investigate which biochemical and physiological pathway(s) they are involved in.  We have identified, cloned, sequenced and analyzed expressed sequence tags (ESTs) related to FHB resistance by comparing the differential expression of genes between FHB inoculated and water-inoculated Sumai 3, a FHB-resistant spring wheat cultivar. Wheaton, a susceptible spring wheat cultivar, is also used as a negative control. EST profiles were revealed by a silver-staining based mRNA differential display (DDRT-PCR) technology from spike samples. A total of 144 PCR primer combinations were tested. Several gene expression patterns were observed: 1) constitutively expressed in Sumai 3; 2) constitutively expressed in Wheaton; 3) induced expression in FHB-inoculated Sumai 3 and Wheaton only; 4) induced expression in FHB-inoculated Wheaton only; and 5) induced expression in FHB-inoculated Sumai 3 only. ESTs of the last category are most likely related to FHB resistant genes. Three such ESTs, EST12G, EST15AU and EST15AD, were cloned with PCR-Trap cloning kit (GenHunter Corporation, Nashville, TN) and sequenced using ABI automatic sequencer. A sequence similarity-search of GeneBank data base revealed that EST15AU is 94% similar to part of a wheat mRNA for polypeptide elogation factor 1 beta’; three regions of EST15AD are homologous (with 86% identity) with an EST sequence from a pathogen induced sorghum bicolor cDNA; EST12G is almost identical (with 99% identity) to a part of minus strand of a wheat gene for chloroplast ATP synthase CF-O subunit I and III.  Two Fusarium ESTs that were more abundantly expressed in Sumai 3 than in Wheaton have also been cloned. Confirmation of the accurate relationship of these ESTs with FHB resistance by genetic analysis is on the way.
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