Abstract
Phytophthora sojae is a destructive pathogen of soybean that is widely distributed in the world. The interaction between P. sojae and soybean follows the gene-for-gene model. The use of resistant soybean cultivars is the primary and most effective method to combat the disease. However, variation in the Avr genes of the pathogen enables it to evade host defenses. We collected 81 isolates from four major soybean-production areas in China to analyze the polymorphism of Avr genes in P. sojae field population. The virulence of these isolates towards 14 differential soybean lines indicated complex pathotypes in P. sojae field population in China. In this study we found that Rps1c, which is cognate with Avr1c, could be deployed in Heilongjiang, Shandong, and Jiangsu Provinces but not in Anhui Province. To determine the mechanism by which Avr1c escapes recognition by Rps1c, we analyzed the polymorphism of Avr1c gene in 50 isolates of a field population of P. sojae and found multiple novel genotypes related to virulence and avirulence. By performing infection assays and gene co-bombardment, we showed that the K105 amino-acid residue was under strong positive selection and was a determinant of the avirulence of Avr1c. Structural analysis showed that K105 was exposed on the surface of the protein, suggesting it to be a critical site for interacting with Rps genes or their associated proteins.
Highlights
Phytophthora root and stem rot caused by Phytophthora sojae
Polymorphism of Avr1c in Chinese isolates In this study, a P. sojae field population was collected from Heilongjiang, Shandong, Anhui and Jiangsu Provinces, the major soybean-production areas in China, where we found that 5.6%, 23.1%, 47.4% and 30.8% of the 81 isolates were virulent on Rps1c, respectively (Fig. 1)
We found that deletion, silencing and point mutations of Avr1c allow it to evade from Rps1c recognition, driving P. sojae to overcome Rps1c-mediated host defenses and providing molecular insight into the coevolution of Avr and Rps genes
Summary
Phytophthora root and stem rot caused by Phytophthora sojae W. Gerdemann) is a destructive disease of soybean. Root rot of soybean caused by P. sojae was first observed in Indiana in 1948 and in Ohio in 1951 (Schmitthenner 1985), which can result in soybean seedlings damping off and cause an annual loss of approximately $1–2 billion on soybean production worldwide (Tyler 2007)
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