Abstract
The soybean ubiquitous urease (encoded by GmEu4) is responsible for recycling metabolically derived urea. Additional biological roles have been demonstrated for plant ureases, notably in toxicity to other organisms. However, urease enzymatic activity is not related to its toxicity. The role of GmEu4 in soybean susceptibility to fungi was investigated in this study. A differential expression pattern of GmEu4 was observed in susceptible and resistant genotypes of soybeans over the course of a Phakopsora pachyrhizi infection, especially 24 h after infection. Twenty-nine adult, transgenic soybean plants, representing six independently transformed lines, were obtained. Although the initial aim of this study was to overexpress GmEu4, the transgenic plants exhibited GmEu4 co-suppression and decreased ureolytic activity. The growth of Rhizoctonia solani, Phomopsis sp., and Penicillium herguei in media containing a crude protein extract from either transgenic or non-transgenic leaves was evaluated. The fungal growth was higher in the protein extracts from transgenic urease-deprived plants than in extracts from non-transgenic controls. When infected by P. pachyrhizi uredospores, detached leaves of urease-deprived plants developed a significantly higher number of lesions, pustules and erupted pustules than leaves of non-transgenic plants containing normal levels of the enzyme. The results of the present work show that the soybean plants were more susceptible to fungi in the absence of urease. It was not possible to overexpress active GmEu4. For future work, overexpression of urease fungitoxic peptides could be attempted as an alternative approach.Electronic supplementary materialThe online version of this article (doi:10.1007/s11103-012-9894-1) contains supplementary material, which is available to authorized users.
Highlights
The soybean plant (Glycine max) is affected by several diseases that negatively affect plant yield, eventually resulting in significant crop losses (Sinclair and Hartman 1999)
The role of GmEu4 in soybean susceptibility to fungi was investigated in this study
The transcript levels of GmEu4 in soybeans inoculated with P. pachyrhizi were determined by RT-qPCR
Summary
The soybean plant (Glycine max) is affected by several diseases that negatively affect plant yield, eventually resulting in significant crop losses (Sinclair and Hartman 1999). Plant Mol Biol (2012) 79:75–87 pachyrhizi, fungicides are the only efficient measure to avoid crop losses. This measure often results in increasing economic and environmental costs (Miles et al 2007). Ureases (EC 3.5.1.5) are nickel-dependent metalloenzymes that catalyse the conversion of urea to ammonia and carbon dioxide, allowing organisms to use exogenous and internally generated urea as a nitrogen source (Dixon et al 1975; Krajewska 2009). These enzymes are synthesised by numerous organisms, including plants, fungi and bacteria (Follmer 2008; Krajewska 2009). The ubiquitous urease is involved in recycling metabolically derived urea (Polacco et al 1985; Stebbins and Polacco 1995; Witte et al 2002), but an assimilatory role for the abundant seed urease has not been demonstrated far (Carlini and Polacco 2008)
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