Abstract
Plant roots are exposed to penetration by different biotrophic and necrotrophic fungi. However, plant immune responses vary, depending on the root-penetrating fungus. Using qRT-PCR, changes over time in the systemic transcriptional expression of the polyphenol biosynthesis-related genes were investigated in sunflower plants in response to colonization with Rhizophagus irregularis and/or infection with Rhizoctonia solani. The results demonstrated that both fungi systemically induced the transcriptional expression of most of the addressed genes at varying degrees. However, the inducing effect differed according to the treatment type, plant organ, targeted gene, and time stage. The inducing effect of R. irregularis was more prevalent than R. solani in the early stages. In general, the dual treatment showed a superior inducing effect over the single treatments at most of the time. The hierarchical clustering analysis showed that cinnamate-4-hydroxylase was the master expressed gene along the studied time period. The cell wall lignification was the main plant-defensive-mechanism induced. In addition, accumulations of chlorogenic acid, flavonoids, and anthocyanins were also triggered. Moreover, colonization with R. irregularis improved the plant growth and reduced the disease severity. We can conclude that the proactive, rather than curative, colonization with R. irregularis is of great importance, owing to their protective and growth-promoting roles, even if no infection occurred.
Highlights
Helianthus annuus L., which is widely known as a common sunflower, is among the most important oil crops in the world, including Egypt
Changes over time in the systemic transcriptional expression levels of the polyphenol biosynthesis-related genes were monitored in the sunflower leaves at 3, 7, 14, 21, and 28 days-postinoculation with R. solani to investigate the cellular responses against root colonization with R. irregularis and/or infection with R. solani
Concerning sunflower leaves, the results that were obtained from Quantitative Real-Time PCR (qRT-PCR) showed that either R. solani treatment or dual treatment with R. irregularis and R. solani, except at 3 dpi, led to considerable up-regulations of the transcriptional expression level of C4H higher than PAL1 gene (Figure 2a)
Summary
Helianthus annuus L., which is widely known as a common sunflower, is among the most important oil crops in the world, including Egypt. Rhizoctonia solani J.G. Kühn 1858 (Family: Ceratobasidiaceae), which is the causal agent of Rhizoctonia root rot of sunflower, is one of the most destructive soil- and seed-borne phytopathogenic fungi, which infects a wide range of plant hosts resulting in high yield losses [3,4,5]. Kühn 1858 (Family: Ceratobasidiaceae), which is the causal agent of Rhizoctonia root rot of sunflower, is one of the most destructive soil- and seed-borne phytopathogenic fungi, which infects a wide range of plant hosts resulting in high yield losses [3,4,5] This necrotrophic pathogen produces sclerotia (overwintering structures), which can survive for many years in the soil or plant debris and germinate, at the favorable conditions, to give mycelia, which attack the sunflower seedlings, causing necrotic lesions on the root and stem at the soil line (collar region) [6]. In addition to root rot, R. solani can cause various diseases on several plants, such as white blight, brown patch, aerial blight, sheath blight, damping-off, and target spot [7]
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