Mycopath (2020) 18(1): 1-6 Research Article Mycopath (2020) 18(1): 1-6 Early events involved in barley response to phytopathogenic fungi with different lifestyles *Antonious Al-Daoude, Mohammed Jawhar, Eyad Al-Shehadah Amina Shoaib and Mohammed Imad Eddin Arabi Department of Molecular Biology and Biotechnology, AECS, P. O. Box 6091, Damascus, Syria *Corresponding author’s email: ascientific@aec.org.sy Abstract Broad spectrum of different fungal pathogenic lifestyles can infect barley plants, most of which are responsible for significant annual crop losses. Understanding of gene expression that take place at the earliest stages of infection would be a necessary step for describing the initial mechanism between barley and the pathogen interactions. The purpose of the present work was to monitor the expression of some well-identified genes PR1, PR2, PR3,PR5, PAL and SGT1 during interaction of resistant barley plants with three economically important diseases viz. spot blotch (Cochliobolus sativus), scald (Rhynchosporium secalis) and powdery mildew (Blumeria graminis) at very early stages of disease development. Data demonstrated a remarkable contradiction in the gene expression patterns between barley and pathogens interactions 12 and 24 hours post inoculation (hpi), and all of them showed significant differential expressions compared to the control plants. The most significant differences were balanced in SGT1 expression which was 3.86 (C. sativus) and 2.5 (R. secalis and B. graminis) folds higher at 12 hpi as compared with the corresponding control treaments. The results revealed that barley plants activated various resistance mechanisms against the three pathogens 12 hpi and increased dramatically at 24 hpi, and the same defense-related genes expression were changed in adaptation to the each fungus. Overall, this work provides insight into a signaling pathway that accounts for classical gene expression changes at very early times of infection, elicited during barley interaction with fungal pathogens having various lifestyles. Keywords: Barley, Defense response, Powdery mildew, Quantitative PCR, Scald, Spot blotch. Introduction Research into plant defense responses at early infection stages by fungal pathogen is considered very important for pathogenesis studies and plant breeding programs. Recently, with the applying proteomics, genomics and transcriptomics techniques, different biochemical events can occur at very early stages of plant pathogen interactions (Kumar and Kirti, 2015; Zhao et al., 2019). Since plants have innate immune systems that can at early stages distinguish the presence of pathogens and thus activate defense responses (Chowdhury et al., 2017). Therefore, the biochemical mechanisms involved in plant resistance to these fungal pathogens are highly dynamic inducing both direct and indirect defense responses. As a consequent, increasing our understanding of these protective mechanisms is still needed. It has been reported that plant leaves motivate the defense mechanisms 3 hpi in maize inoculated with Colletotrichum graminicola, 24 hpi in wheat challenged with yellow rust, and 12 hpi in rice (Liu et al., 2016). These examples showed that plants responses against pathogens started rapidly after coming in touch with each other and then various signal pathways to achieve disease resistance were triggered. Therefore, defense mechanisms and signaling pathways remain to be investigated. Spot blotch caused by the necrotrophic fungus Cochliobolus sativus, scald caused by the hemibiotroph fungus Rhynchosporium secalis, and powdery mildew caused by the biotrophic fungus Blumeria graminis f. sp. hordei, are among the most important fungal pathogens of barley causing economic crop losses globally (Gangwar et al., 2018). Barley plants have developed a complex defense system against these diverse pathogens; however, the molecular events at very early stages of infection are not yet completely understood (Glazebrook, 2005). Changes in the expression levels of a large number of defense-related genes can be estimated in barley plants during early stages of fungal pathogen infection, which considered a key defense genes (Stephens et al., 2008; Shen et al., 2017). Therefore, it is useful to improve our understanding concerning the changes of these genes in barley challenged by the four fungal pathogens with different lifestyles. Quantitative PCR (qPCR) is reported to be an effective method for measuring the relative expression level of particular genes in plant species infected with different fungal pathogens (Nolan et al., 2006; Derveaux et al., 2010). Activation defense responses have been considered to be as one of the first reaction levels that usually noticed after disease infection (Kumar et