Abstract
The fungus Stagonospora nodorum Berk. is the causative agent of Septoria nodorum blotch (SNB) of wheat. The most important factors of Stagonospora nodorum virulence include numerous fungal necrotrophic effectors (NEs) encoded by SnTox genes. They interact with the matching products of host susceptibility genes (Snn). SnTox-Snn interactions are mirror images of classical gene-for-gene interactions and lead to the development of disease. We have studied the SnTox3-Snn3 interaction, resulting in the development of infection on leaves and formation of extensive lesions. The mechanism of SnTox3 action is likely to be linked to the regulation of redox metabolism and the influence on ethylene synthesis in the wheat plants, although the molecular mechanisms are not fully unveiled. To characterize the SnTox3-Snn3 interaction, we used S. nodorum isolates differing in the expression of the NEs genes SnTox3 (SnB (Tox3+), Sn4VD (Tox3–)) and two soft spring wheat (Triticum aestivum L.) cultivars, contrasting in resistance to the SNB agent and differing in the allelic composition of the susceptibility locus Snn3-B1: Kazakhstanskaya 10 (susceptible) and Omskaya 35 (resistant). We carried out a comparative assessment of the transcriptional activity patterns of genes responsible for ethylene biosynthesis (TaACS1, TaACО) and signaling pathway (TaEIL1, TaERF1) by real-time PCR and estimated the redox state of wheat plants infected with different isolates of S. nodorum by spectrometry. The induction of ethylene biosynthesis and signaling has been shown to result from gene-for-gene interaction between Snn3-B1 and SnTox3. The results of plant redox status estimation showed that ethylene inhibited accumulation of hydrogen peroxide in SnTox3-sensitive genotypes by regulating the operation of various pro-/antioxidant enzymes at the transcriptional and posttranslational levels. Our results suggest that NE SnTox3 influences ethylene biosynthesis and signaling, thereby regulating redox metabolism in infected wheat plants as necessary for successful host colonization at the initial phases of infection, which ultimately leads to extensive lesions due to fast pathogen reproduction.
Highlights
Wheat, a staple crop, has been attacked by various kinds of leaf spot diseases in recent decades, and Septoria nodorum blotch (SNB) ranks among the most injurious ones
We showed the negative role of ethylene in the development of wheat plant resistance to S. nodorum (Veselova et al, 2016)
PCR diagnostics of the allelic state of the Snn3-B1 locus was performed in two soft spring wheat cultivars, Kazakhstanskaya 10 (Kaz10) and Omskaya 35 (Om35)
Summary
A staple crop, has been attacked by various kinds of leaf spot diseases in recent decades, and Septoria nodorum blotch (SNB) ranks among the most injurious ones. It is caused by the fungal pathogen Stagonospora nodorum Berk. It has been shown that among the most important factors of virulence of S. nodorum are the numerous necrotrophic effectors (NEs), formerly referred to as host-specific (selective) toxins (Phan et al, 2016; McDonald, Solomon, 2018). The interaction in the wheat–S. nodorum pathosystem is of the gene-for-gene type (McDonald, Solomon, 2018). These relationships are confirmed by the fact that products of the pathogen virulence genes (=host-specific toxins) (SnTox) cause compatibility, i. Eight SnTox-Snn interactions are known, while only three genes encoding NEs (SnToxA, SnTox, and SnTox3) have been cloned from the pathogen, and only two susceptibility genes (Tsn and Snn1) have been cloned from wheat (Phan et al, 2016; Shi et al, 2016)
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