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Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is one of the most destructive foliar diseases that affect soybeans. Developing resistant cultivars is the most cost-effective, environmentally friendly, and easy strategy for controlling the disease. However, the current understanding of the mechanisms underlying soybean resistance to P. pachyrhizi remains limited, which poses a significant challenge in devising effective control strategies. In this study, comparative transcriptomic profiling using one resistant genotype and one susceptible genotype was performed under infected and control conditions to understand the regulatory network operating between soybean and P. pachyrhizi. RNA-Seq analysis identified a total of 6540 differentially expressed genes (DEGs), which were shared by all four genotypes. The DEGs are involved in defense responses, stress responses, stimulus responses, flavonoid metabolism, and biosynthesis after infection with P. pachyrhizi. A total of 25,377 genes were divided into 33 modules using weighted gene co-expression network analysis (WGCNA). Two modules were significantly associated with pathogen defense. The DEGs were mainly enriched in RNA processing, plant-type hypersensitive response, negative regulation of cell growth, and a programmed cell death process. In conclusion, these results will provide an important resource for mining resistant genes to P. pachyrhizi infection and valuable resources to potentially pyramid quantitative resistance loci for improving soybean germplasm. [ABSTRACT FROM AUTHOR]

Key message: In this study, Rpp6907, a novel resistance gene/allele to Phakopsora pachyrhizi in soybean, was mapped in a 111.9- kb region, including three NBS-LRR type predicted genes, on chromosome 18. Abstract: Soybean rust caused by Phakopsora pachyrhizi Sydow has been reported in numerous soybean-growing regions worldwide. The development of rust-resistant varieties is the most economical and environmentally safe method to control the disease. The Chinese soybean germplasm SX6907 is resistant to P. pachyrhizi and exhibits immune reaction compared with the known Rpp genes. These characteristics suggest that SX6907 may carry at least one novel Rpp gene/allele. Three F populations from the crosses of SX6907 (resistant) and Tianlong 1, Zhongdou40, and Pudou11 (susceptible) were used to map the Rpp gene. Three resistance responses (immune, red-brown, and tan-colored lesion) were observed from the F individuals. The segregation follows a ratio of 1(resistance):2(heterozygous):1(susceptible), indicating that the resistance in SX6907 is controlled by a single incomplete dominant gene (designated as Rpp6907). Results showed that Rpp6907 was mapped on soybean chromosome 18 (molecular linkage group G, MLG G) flanked by simple sequence repeat (SSR) markers SSR24 and SSR40 at a distance of 111.9 kb. Among the ten genes marked within this 111.9-kb region between the two markers, three genes ( Glyma18g51930, Glyma18g51950, and Glyma18g51960) are nucleotide-binding site and leucine-rich repeat-type genes. These genes may be involved in recognizing the presence of pathogens and ultimately conferring resistance. Based on resistance spectrum analysis and mapping results, we inferred that Rpp6907 is a novel gene different from Rpp1 in PI 200492, PI 561356, PI 587880A, PI 587886, and PI 594538A, or a new Rpp1- b allele. [ABSTRACT FROM AUTHOR]

Soybean rust caused by P hakopsora pachyrhizi is a destructive foliar disease in nearly all soybean-producing countries. Understanding the host responses at the molecular level is certainly essential for effective control of the disease. To identify proteins involved in the resistance to soybean rust, differential proteomic analysis was conducted in soybean leaves of a resistant genotype after P . pachyrhizi infection. A total of 41 protein spots exhibiting a fold change >1.5 between the non-inoculated and P. pachyrhizi-inoculated soybean leaves at 12 and 24 h postinoculation (hpi) were unambiguously identified and functionally grouped into seven categories. Twenty proteins were up-regulated and four proteins were down-regulated at 12 hpi, whereas 18 proteins were up-regulated and eight proteins were down-regulated at 24 hpi. Generally, proteins involved in photosynthesis were down-regulated, whereas proteins associated with disease and defense response, protein folding and assembly, carbohydrate metabolism and energy production were up-regulated. Results are discussed in terms of the functional implications of the proteins identified, with special emphasis on their putative roles in defense. Abundance changes of these proteins, together with their putative functions reveal a comprehensive picture of the host response in rust-resistant soybean leaves and provide a useful platform for better understanding of the molecular basis of soybean rust resistance. [ABSTRACT FROM AUTHOR]