Transcriptional and physiological responses of wheat Triticum aestivum to a combination of abiotic and biotic stress

Abstract

Plant responses to simultaneous biotic and abiotic stresses involve the activation of multiple signalling pathways that often interact in a synergistic or an antagonistic manner. Recent studies have shown that the plant response to a combination of stresses differ to those that occur when exposed to a single stress. The aim of the present study is to investigate the response of wheat (Triticum aestivum) to both salinity and aphid Sitobion avenae infestation, applied singly and in combination, at the physiological and transcriptional levels, to provide a better understanding of the impact of abiotic and biotic interactions and cross tolerance in wheat. These two forms of stress were selected since they are known to have a major impact on crop productivity. Wheat genotype 122-1 was shown to be tolerant to salt (160 mM NaCl) on the basis of biomass; accumulating high levels of Na+ in the shoots and was partially resistant to aphids in terms of fecundity. Pretreatment of this genotype with salt significantly (p<0.001) reduced aphid fecundity (by 37%) relative to its control, indicating enhanced resistance to aphids. This positive interaction between salt and aphid stress was investigated at 6h and 24h post aphid infestation on the wheat transcriptome. Microarray analysis indicated common and specific gene expression patterns of the 61.290 transcripts differentially regulated in response to salt stress alone, aphid infestation alone and dual stress compared to the controls. Dual stress specifically and strongly increased the transcription level of the following genes assigned to jasmonate synthesis encoding lipoxygenase (LOX), abiotic stress (heat), miscellaneous enzyme families (acid and other phosphatases) at 6h, and secondary metabolism (phenylpropanoids) at 24h. Furthermore, based on functional classification analysis, several categories which were shown to be significantly activated by dual stress such as cytokinin hormone synthesis and MAP kinases signalling were not, however, significantly changed under either salt stress or aphid infestation alone. The current study demonstrated that jasmonate hormone signalling pathways antagonized those of salicylic acid under dual stress and aphid infestation at 6 h. Results suggests that the interaction between combined salinity and aphids stresses caused distinct alteration in gene expression patterns that could not be detected under either of the two stresses when applied individually. This study proposes that the activation of specific genes involved in the acquisition of defence/tolerance, such as those encoding cytochrome P450 and MYB domain transcription factor families, due to prior exposure to salt may enhance subsequent tolerance to aphids. The present study sheds light on candidate genes with putative functions in the crosstalk and the acquisition of cross tolerance and provides new insights on wheat response to multiple stress conditions. Such information is a prerequisite for enhancing crop tolerance to a broad-spectrum of stress.