Cloning of genes involved in the early response of wheat towards Russian wheat aphid infestation

English: The interaction between wheat (Triticum aestivum) and the Russian wheat aphid (Diuraphis noxia) was investigated on a molecular level. The resistant cultivar, Tugela DN1, was infested with the Russian wheat aphid and tissue harvested at 3 hour time intervals for 24 hours. Differential display RT-PCR was used to clone genes that were inducibly expressed using primers specific to the conserved subdomain VIb of the kinase domain of protein kinases. Differentially expressed genes were found as early as three hours after infestation. These fragments were cloned and sequenced. A total of 11 differentially expressed cDNA fragments were analyzed. Four showed homology to genes encoding proteins involved in normal cellular metabolism, such as the Rubisco large subunit, indole-3-gylcerol phosphate lyase that produces indole that could act as a volatile messenger molecule, triose-phosphate isomerase that is involved in glycolysis and 2- isopropylmalate synthase that is involved in leucine biosynthesis. Of the other cDNAs, three clones showed homology to several hypothetical proteins with no defined functions, while the other three showed no homology at all with any other known genes. One of the unknown clones (D20) was selected for further analysis. The gene was inducibly expressed only in the infested resistant plants, but not in the infested susceptible plants. The expression of the gene was induced within 3 h after infestation reaching a maximum expression level 6 h.p.i. The gene is present as a single copy within the genomes of susceptible and 5 different resistance lines. An attempt to clone the full length gene was only partially successful since after the sequences were combined homology was found with several hypothetical genes from rice and maize. However, no identity and function could be given.