An investigation into possible sugar signaling events during the infection of wheat with Puccinia triticina

English: Puccinia triticina (leaf rust) is an obligate biotrophic fungus. It is a major pathogen of Triticum aestivum (wheat) all over the world. In a previous study, two differentially expressed genes were cloned from resistant wheat infected with P. triticina. According to the sequence analysis, the first encoded a cell wall invertase (TaCwi01) and the other a monosaccharide transporter (TaMst01). These two genes and their encoded proteins appear to play a role during sugar signaling. Sugar signaling has already been described in several plant-pathogen interactions. In this study, the presence of sugar signaling as well as the roles of TaCwi01, TaMst01 and a hexokinase gene in the leaf rust – wheat interaction were investigated. Gene expression studies of all three genes showed both early as well as late changes in expression. TaCwi01 gene expression showed an early induction in IS plants at 3 hpi followed by an immediate and complete inhibition until 36 hpi. Expression in IR plants was repressed for the duration of the study with a transient increase at 21 hpi. Enzyme activity analysis revealed a similar pattern of the expression with a significant activation in both IS and IR plants at 27 and 24 hpi respectively. Results of TaMst01 expression revealed both an early induction at 3 to 6 hpi and a late induction at 33 hpi in IS and IR plants. The later induction in expression of TaMst01 was reflected in the significant increase in MST activity at 30 hpi. Hexokinase expression analysis showed a slight increase in expression from 0 to 6 hpi in both IS and IR plants. This was again associated with increased enzyme activity shortly after infection. Furthermore it was shown that due to a SCPU domain in the polypeptide sequence of TaCwi01, it is possible that this gene could have originated from the pathogen. It was concluded that a putative sugar signaling took place during the infection of wheat with leaf rust and that all three genes played a definite role.