Characterisation of gene sequences induced in barley after pathogen infection

M.Sc.Barley (Hordeum vulgare) production is a vital constituent of the South African economy. Many pathogens reside on barley, which lead to low quality and yield. One of the most prominent barley pathogens, Fusarium graminearum, is the causal agent of small grain scab. F. graminearum resistance to barley is regulated by multiple genes referred to as quantitative trait loci (QTL), which makes it difficult to breed for resistance in new cultivars. Each of these genes contributes to a specific defence area and collectively counteracts Fusarium infection and spread in the barley plant. The aim of this project was to isolate and identify induced genes after infection of three leave stage barley with F. graminearum. These genes were isolated through the use of Suppression subtractive hybridisation (SSH), cloned and then sequenced. From this data set three transcript derived fragments (TDFs) sharing homology to known genes were selected and their expression profiles were studied through Northern blot analysis. Three TDFs shared homology with known genes namely a putative protease inhibitor-related protein, a senescence associated gene, and a manganese superoxide dismutase (MnSOD). These TDFs were previously also recognised for their function in host pathogen interactions. The expression analysis done using Northern blots showed up-regulation of the three fragments after inoculation. These results indicated that all the TDFs studied may play a role in the defence reaction of barley infected with F. graminearum, where both senescence and proteinase inhibitors could limit infection as well as spread and MnSODs might be a protective enzyme against oxidative stress. The results of this study indicated that all of the identified TDFs had database matches to proteins identified during stress responses. Furthermore, the Northern blot results indicated that all the TDFs studied could play a role in the defence reaction of F. graminearum infected barley. These TDFs will form the basis of further studies into the interaction between barley and F. graminearum. The results form this study will add to our knowledge of the interaction between barley and a necrotrophic pathogen. This will aid in understanding how cereal pathogens deal with pathogen attack and will aid in development of new more tolerant barley cultivars