Abstract
Fungal diseases lead to significant losses in soybean yields and a decline in seed quality; such is the case of the Asian soybean rust and anthracnose caused by Phakopsora pachyrhizi and Colletotrichum truncatum, respectively. Currently, the development of transgenic plants carrying antifungal defensins offers an alternative for plant protection against pathogens. This paper shows the production of transgenic soybean plants expressing the NmDef02 defensin gene using the biolistic delivery system, in an attempt to improve resistance against diseases and reduce the need for chemicals. Transgenic lines were assessed in field conditions under the natural infections of P. pachyrhizi and C. truncatum. The constitutive expression of the NmDef02 gene in transgenic soybean plants was shown to enhance resistance against these important plant pathogens. The quantification of the P. pachyrhizi biomass in infected soybean leaves revealed significant differences between transgenic lines and the non-transgenic control. In certain transgenic lines there was a strong reduction of fungal biomass, revealing a less severe disease. Integration and expression of the transgenes were confirmed by PCR, Southern blot, and qRT-PCR, where the Def1 line showed a higher relative expression of defensin. It was also found that the expression of the NmDef02 defensin gene in plants of the Def1 line did not have a negative effect on the nodulation induced by Bradyrhizobium japonicum. These results indicate that transgenic soybean plants expressing the NmDef02 defensin gene have a substantially enhanced resistance to economically important diseases, providing a sound environmental approach for decreasing yield losses and lowering the burden of chemicals in agriculture.
Highlights
Soybean [Glycine max (L.) Merryll] is one of the most economically important crops worldwide (Hartman et al, 2011; Rosa et al, 2015), its outstanding role in feeding the world through its contribution of both protein meal and vegetable oil, is jeopardized by the attack of fungal diseases at all growth stages, producing a considerable reduction in yields (Hartman et al, 2015).Nmdef02 Soybean Resistance to FungiAsian soybean rust caused by Phakopsora pachyrhizi (Sydow & Sydow) is the most destructive disease in soybean, causing early defoliation while affecting the weight and quality of the seeds (Hartman et al, 2005)
Three transgenic lines obtained by self-pollination (T4) that were selected for resistance to Asian soybean rust and nontransgenic plants were grown on an experimental area of the National Institute of Agricultural Sciences (INCA), Mayabeque province, during the winter (November–March)
We obtained the first evidence of resistance to the hemibiotrophic fungus C. truncatum and the biotrophic fungus P. pachyrhizi in soybean plants transformed with the NmDef02 defensin gene under the 35S constitutive promoter
Summary
Soybean [Glycine max (L.) Merryll] is one of the most economically important crops worldwide (Hartman et al, 2011; Rosa et al, 2015), its outstanding role in feeding the world through its contribution of both protein meal and vegetable oil, is jeopardized by the attack of fungal diseases at all growth stages, producing a considerable reduction in yields (Hartman et al, 2015). Defensins may inhibit the growth of a wide range of microorganisms and phytopathogenic insects; they may be involved in abiotic stress adaptation (Tavares et al, 2008) This means that do defensins produce a defense against plant pathogens, but they generate adaptations to difficult conditions, a characteristic that makes them even more attractive for modern agriculture. The efficiency of the symbiosis of Bradyrhizobium japonicum with transgenic soybean plants carrying defensin was evaluated, since the association with this bacterium is essential for atmospheric nitrogen fixation in soybean plants, eliminating the need for chemical nitrogen fertilization This strategy is in line with the goals of decreasing yield losses, decreasing the use of chemicals, and contributing to an increase of 100% in yields that are required for sustaining a world population of nearly 10 billion people in 2050, all of which are challenges acknowledged by Generation Agriculture
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