Gene Expression Profiling And Silencing Reveal The Relationship Between Wheat Defense Genes And The Resistance Response Of Wheat To Powdery Mildew

Powdery mildew is a wheat fungal disease caused by Blumeria graminis f. sp. tritici (Bgt). Its frequent occurrence and worldwide spread seriously impact wheat production. Although improved cultivation techniques and fungicides have been adopted for many years, they are not the most effective and environmentally friendly ways to control crop disease. Practice has proved that the fundamental way to control crop diseases is to introduce resistance genes through genetic material modifying and improving by the way of traditional or molecular breeding, which greatly depends on an in-depth understanding of the molecular mechanism of plant-pathogen interactions and the cloning and functional analysis of important genes. In this study five important wheat defense response genes, one thiosulfate sulfur transferase gene TaTST, two chitinase genes TaCht2and TaCht4, and two (3-1,3-glucanase genes TaGlb3s2and TaGlb3s6, were chose to conduct in-depth analysis of their roles in wheat resistance reaction to powdery mildew.1Study on the relationship between TaTST, a wheat thiosulfate sulfurtransferase gene, and the resistance response of wheat to powdery mildewPlant thiosulfate sulfurtransferase (TST), which participates in sulfur metabolism, removal of cyanide, generation and removal of reactive oxygen species (ROS), is closely related to plant disease resistance. The wheat TST-encoding gene TaTST was induced by the powdery mildew pathogen fungus Blumeria graminis f. sp. tritici (Bgt) in both the resistant and the susceptible wheat near-isogenic lines. Two expression peaks of TaTST were found from0to48h after inoculation of Bgt, corresponding to the initial contact and recognition between the host cell and Bgt and the invasion attempt of appressoria and haustoria formation. The two expression peaks were also in agreement with the two oxygen burst reactions. The induced expression level of TaTST was significantly higher in the susceptible line than in the resistant line, which may result in excessive removal of ROS as a response to Bgt infection and so contribute to the process of disease susceptibility. TaTST also involved in the process of disease resistance. The method of virus-induced gene silencing (VIGS) was used to silence the TaTST gene of the resistant line. Although TaTST silencing plants did not produce visible mildew spots or lesions, they showed reduction of resistance to powdery mildew with the increased successful penetration rate and limited elongation of secondary hypha. Decreased density of papilla and delayed H2O2spreading in the Bgt-challenged host cells of the VIGS plants suggest that TaTST possibly affects the Bgt penetration process in resistance response through participating in the ROS accumulation and spread and the papilla formation at early stage of wheat-Bgt interaction.2. Study on the relationship between chitinase and β-1,3-glucanase-eneoding genes and the resistance response of wheat to powdery mildew As two main types of pathogenesis related protein, chitinase and β-1,3-glucanase play important roles in plant fungal resistance. Previous researches have indicated that chitinase and β-1,3-glucanase inhibit fungi growth by degrading chitin and (3-glucan, both major structural cell wall polysaccharides, and chitin or glucan oligomers may also function as elicitors to activate further plant defense reactions. Here two chitinase-encoding genes(TaCht2and TaCht4) and two β-1,3-glucanase-encoding genes (TaGlb3s2and TaGlb3s6) are chose to study their functions in the resistance response of wheat the powdery mildew by gene expression profiling analysis and the gene silencing method. Two-peak induced expression profiles of TaCht2, TaCht4and TaGlb3s2were found in wheat powdery mildew resistant and near-isogenic susceptible lines0-48h after inoculation of Bgt. But detailed induced expression patterns were somewhat different among these three genes. The method of virus-induced gene silencing (VIGS) was used to silence target genes in the resistant line. Quantitative PCR and enzyme activity assay demonstrated that the expression of target genes decreased to different degrees in gene-silenced plants. Observation48h after inoculation of Bgt showed significantly increased Bgt successful penetration rate, indicating that gene silencing reduce the level of plant resistance. Bgt penetration was most obviousiy observed in TaCht4-silenced plants with the greatest penetration rate of68.9%, which is consistent with the higher silencing effect of this gene. Among the four genes, TaGlb3s2silencing had the most stable impact on penetration rate of Bgt.