Abstract
Our recent work has shown that a rice thizospheric natural isolate, a Pantoea sp (hereafter EA106) attenuates Arsenic (As) uptake in rice. In parallel, yet another natural rice rhizospheric isolate, a Pseudomonas chlororaphis (hereafter EA105), was shown to inhibit rice blast pathogen Magnaporthe oryzae. Considering the above, we envisaged to evaluate the importance of mixed stress regime in rice plants subjected to both As toxicity and blast infections. Plants subjected to As regime showed increased susceptibility to blast infections compared to As-untreated plants. Rice blast pathogen M. oryzae showed significant resistance against As toxicity compared to other non-host fungal pathogens. Interestingly, plants treated with EA106 showed reduced susceptibility against blast infections in plants pre-treated with As. This data also corresponded with lower As uptake in plants primed with EA106. In addition, we also evaluated the expression of defense related genes in host plants subjected to As treatment. The data showed that plants primed with EA106 upregulated defense-related genes with or without As treatment. The data shows the first evidence of how rice plants cope with mixed stress regimes. Our work highlights the importance of natural association of plant microbiome which determines the efficacy of benign microbes to promote the development of beneficial traits in plants.
Highlights
Rice is the food for over half the world’s population and contributes as much as 80% of the daily caloric intake in many South Asian countries (Dawe et al, 2010)
Nipponbare seedlings primed with EA106 and treated with As(III) showed significant reduction in grain As content compared to untreated mock plants (Supplementary Figure 1)
We have identified a suite of nonpathogenic, rice-associated bacteria, Pantoea sp. (EA106) from roots of rice grown in North American rice paddy fields and have shown that they promote healthy rice growth and enhance the oxidizing potential of the rhizosphere (Lakshmanan et al, 2015)
Summary
Rice is the food for over half the world’s population and contributes as much as 80% of the daily caloric intake in many South Asian countries (Dawe et al, 2010). Paddy rice grown in South East Asia and in the arsenic (As) hotspots accumulates inorganic As leading to elevated arsenic in rice grain, contributing to large-scale mass As-poisoning (Huq, 2008). Chronic low-level exposure increases incidence of multiple cancers and causes disfigurement and recurring diarrhea. This is exacerbated by the fact that elevated As concentrations in soil is phytotoxic and can contribute to decreased grain fill, lowered yield and reduced food availability (Abedin et al, 2002; Panaullah et al, 2009). Novel strategies are needed to simultaneously decrease the As content and increase nutritional value in rice grains
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