Abstract
Soil salinity and drought are among the most serious agricultural and environmental problems of today. Therefore, investigations of plant resistance to abiotic stress have received a lot of attention in recent years. In this study, we identified the complete coding sequence of a 3′-phosphoadenosine-5′-phosphatase protein, ApHal2, from the halotolerant yeast Aureobasidium pullulans. Expression of the ApHAL2 gene in a Saccharomyces cerevisiae hal2 mutant complemented the mutant auxotrophy for methionine, and rescued the growth of the hal2 mutant in media with high NaCl concentrations. A 21-amino-acids-long region of the ApHal2 enzyme was inserted into the Arabidopsis thaliana homologue of Hal2, the SAL1 phosphatase. The inserted sequence included the META motif, which has previously been implicated in increased sodium tolerance of the Hal2 homologue from a related fungal species. Transgenic Arabidopsis plants overexpressing this modified SAL1 (mSAL1) showed improved halotolerance and drought tolerance. In a medium with an elevated salt concentration, mSAL1-expressing plants were twice as likely to have roots in a higher length category in comparison with the wild-type Arabidopsis and with plants overexpressing the native SAL1, and had 5% to 10% larger leaf surface area under moderate and severe salt stress, respectively. Similarly, after moderate drought exposure, the mSAL1-expressing plants showed 14% increased dry weight after revitalisation, with no increase in dry weight of the wild-type plants. With severe drought, plants overexpressing native SAL1 had the worst rehydration success, consistent with the recently proposed role of SAL1 in severe drought. This was not observed for plants expressing mSAL1. Therefore, the presence of this fungal META motif sequence is beneficial under conditions of increased salinity and moderate drought, and shows no drawbacks for plant survival under severe drought. This demonstrates that adaptations of extremotolerant fungi should be considered as a valuable resource for improving stress-tolerance in plant breeding in the future.
Highlights
Water scarcity results in major agricultural losses worldwide, and is responsible for severe food shortages in developing countries [1]
Modified SAL1 We have shown that ApHal2 protein is a phosphoadenosine 59-phosphate (PAP) phosphatase, with the key role in tolerance to environmental sodium
For the yeast S. cerevisiae, the enzyme determining the Na+ toxicity of the cells is the PAP phosphatase Hal2 [22], homologues of which have been identified in many fungi [26,27,28] and plants [7], and which are highly conserved
Summary
Water scarcity results in major agricultural losses worldwide, and is responsible for severe food shortages in developing countries [1]. Despite significant efforts and some encouraging results, attempts to develop genetically modified salt-tolerant crops lines/cultivars have not yielded the desired results to date [3]. With the exception of ion transporters, the same groups of genes have been targeted in efforts to improve drought tolerance in plants [5]. The majority of used genes originated from either relatively stress-sensitive organisms or from prokaryotic organisms that are phylogenetically and functionally less related to plants. Stress-tolerant fungi do not have these disadvantages, they have so far been largely overlooked as sources of stresstolerance-conferring genes [6]. We show that these fungal species can offer novel ways for the improvement of stress tolerance in plants
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