Nitrogen fertilizers drastically increased yield but are also known toincrease the level of many plant diseases. The interaction between the blast fungus Magnaporthe oryzae and rice is no exception. Improving rice for Nitrogen Use Efficiency is a goal for many breeding program but such improvement may also render plants more susceptible to rice blast. Thus understanding the mechanismsby which nitrogen is inducing blast susceptibility (NIS) is of major importance. In our experimental conditions, we show that fungal growth is affected before and after penetration in the plant but that the final penetration rate is not affected. In order to understand the mechanisms of NIS, we have conducted a dual RNAseq experiment on rice infected tissues. There is no clear-cut indication that differences in defense gene expression before and after infection could be responsible for the NIS phenomen on although the expression of numerous genes belonging to immunity were affected.On the other hand, the fungus perceived small differences in nitrogen amount after penetration and modified the expression of effectors and pathogenicity related proteins. Moreover some rice genes implicated in nitrogen recycling were highly induced during NIS. We further demonstrate that inactivation of one glutamine synthetase gene enhanced plant resistance to M. oryzae and abolished NIS.