Huang H, Nguyen Thi Thu T, He X, Gravot A, Bernillon S, Ballini E, Morel JB.

Front Plant Sci. 2017 Feb 28;8:265. doi: 10.3389/fpls.2017.00265. eCollection 2017.

Abstract

Highlight  Modifications in glutamine synthetase OsGS1-2 expression and fungal pathogenicity underlie nitrogen-induced susceptibility to rice blast. Understanding why nitrogen fertilization increase the impact of many plant diseases is of major importance. The interaction between Magnaporthe oryzae and rice was used as a model for analyzing the molecular mechanisms underlying Nitrogen-Induced Susceptibility (NIS). We show that our experimental system in which nitrogen supply strongly affects rice blast susceptibility only slightly affects plant growth. In order to get insights into the mechanisms of NIS, we conducted a dual RNA-seq experiment on rice infected tissues under two nitrogen fertilization regimes. On the one hand, we show that enhanced susceptibility was visible despite an over-induction of defense gene expression by infection under high nitrogen regime. On the other hand, the fungus expressed to high levels effectors and pathogenicity-related genes in plants under high nitrogen regime. We propose that in plants supplied with elevated nitrogen fertilization, the observed enhanced induction of plant defense is over-passed by an increase in the expression of the fungal pathogenicity program, thus leading to enhanced susceptibility. Moreover, some rice genes implicated in nitrogen recycling were highly induced during NIS. We further demonstrate that the OsGS1-2 glutamine synthetase gene enhances plant resistance to M. oryzae and abolishes NIS and pinpoint glutamine as a potential key nutrient during NIS.

See: https://www.ncbi.nlm.nih.gov/pubmed/28293247

Figure 2: Penetration and growth of M. oryzae in rice plants under different nitrogen regimes. Low or high nitrogen fertilization (0N and 1N; see Section Materials and Methods) was applied to Nipponbare (A) and Kasalath (B) plants which were subsequently inoculated with the Guy11 isolate. At the indicated time after inoculation (1, 2, and 4 dpi), the developmental stage of the fungus was evaluated. Four types of situations were counted: a spore that germinated but did not develop an appressorium (black), a spore with a developed appressorium (dark gray), sites where the fungus had penetrated one cell (light gray) and sites where the fungus had penetrated several cells (white). For each time x treatment combination, a total of 100 events were counted. This experiment was repeated three times and one representative experiment is shown. A Chi square test was used to compare the different percentages (see text). ^***P < 0.001.