The 12-oxo-phytodienoic acid reductases (OPRs) are classified into the two subgroups OPRI and OPRII. The latter proteins participate in jasmonic acid synthesis, while the function of the former ones is as yet unclear. We describe here the characterization of the OPRI gene TaOPR1, isolated from the salinity-tolerant bread wheat (Triticum aestivum) cultivar SR3. Salinity stress induced a higher level of TaOPR1 expression in the seedling roots of cv SR3 than in its parental cultivar, JN177. This induction was abolished when abscisic acid (ABA) synthesis was inhibited. The overexpression of TaOPR1 in wheat significantly enhanced the level of salinity tolerance, while its heterologous expression in Arabidopsis alleviated root growth restriction in the presence of salinity and oxidants and raised the sensitivity to ABA. In Arabidopsis, TaOPR1 promoted ABA synthesis and the ABA-dependent stress-responsive pathway, partially rescued the sensitivity of the Arabidopsis aba2 mutant defective in ABA synthesis to salinity, and improved the activities of reactive oxygen species scavengers and the transcription of their encoding genes while reducing malondialdehyde and reactive oxygen species levels. TaOPR1 did not interact with jasmonate synthesis or the jasmonate signaling pathway. Rather than serving purely as an antioxidant, we believe that TaOPR1 acts during episodes of abiotic stress response as a signaling compound associated with the regulation of the ABA-mediated signaling network.

BackgroundSoil alkalinity shows significant constraints to crop productivity; however, much less attention has been paid to analyze the effect of soil alkalinity on plant growth and development. Shanrong No. 4 (SR4) is an alkalinity tolerant bread wheat cultivar selected from an asymmetric somatic hybridization between the bread wheat cultivar Jinan 177 (JN177) and tall wheatgrass (Thinopyrum ponticum), which is a suitable material for studying alkalinity tolerant associate genes.ResultsThe growth of SR4 plant seedlings was less inhibited than that of JN177 when exposed to alkalinity stress conditions. The root cytosolic Na+/K+ ratio in alkalinity stressed SR4 was lower than in JN177, while alkalinity stressed SR4 contained higher level of nutrient elements than in JN177. SR4 plant seedlings accumulated less malondialdehyde (MDA) and reactive oxygen species (ROS), it also showed higher activity of ROS scavenging enzymes than JN177 under alkalinity stress. The root intracellular pH decreased in both alkalinity stressed JN177 and SR4, however, it was much lower in SR4 than in JN177 under alkalinity stress. The transcriptomes of SR4 and JN177 seedlings exposed to alkalinity stress were analyzed by digital gene expression tag profiling method. Alkalinity stress conditions up- and down-regulated a large number of genes in the seedling roots that play the functions in the categories of transcription regulation, signal transduction and protein modification.ConclusionsSR4 expresses a superior tolerance to alkaline stress conditions which is due to its strong absorbing ability for nutrient ions, a strong regulating ability for intracellular and rhizosphere pH and a more active ROS scavenging ability.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3421-8) contains supplementary material, which is available to authorized users.

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Aquaporins are channel proteins which transport water across cell membranes. We show that the bread wheat aquaporin gene TaTIP2;2 maps to the long arm of chromosome 7b and that its product localizes to the endomembrane system. The gene is expressed constitutively in both the root and the leaf, and is down-regulated by salinity and drought stress. Salinity stress induced an increased level of C-methylation within the CNG trinucleotides in the TaTIP2;2 promoter region. The heterologous expression of TaTIP2;2 in Arabidopsis thaliana compromised its drought and salinity tolerance, suggesting that TaTIP2;2 may be a negative regulator of abiotic stress. The proline content of transgenic A. thaliana plants fell, consistent with the down-regulation of P5CS1, while the expression of SOS1, SOS2, SOS3, CBF3 and DREB2A, which are all stress tolerance-related genes acting in an ABA-independent fashion, was also down-regulated. The supply of exogenous ABA had little effect either on TaTIP2;2 expression in wheat or on the phenotype of transgenic A. thaliana. The expression level of the ABA signalling genes ABI1, ABI2 and ABF3 remained unaltered in the transgenic A. thaliana plants. Thus TaTIP2;2 probably regulates the response to stress via an ABA-independent pathway(s).

SUMMARY Aluminium (Al) stress is a major limiting factor for worldwide crop production in acid soils. In Arabidopsis thaliana, the TAA1‐dependent local auxin biosynthesis in the root‐apex transition zone (TZ), the major perception site for Al toxicity, is crucial for the Al‐induced root‐growth inhibition, while the mechanism underlying Al‐regulated auxin accumulation in the TZ is not fully understood. In the present study, the role of auxin transport in Al‐induced local auxin accumulation in the TZ and root‐growth inhibition was investigated. Our results showed that PIN‐FORMED (PIN) proteins such as PIN1, PIN3, PIN4 and PIN7 and AUX1/LAX proteins such as AUX1, LAX1 and LAX2 were all ectopically up‐regulated in the root‐apex TZ in response to Al stress and coordinately regulated local auxin accumulation in the TZ and root‐growth inhibition. The ectopic up‐regulation of PIN1 in the TZ under Al stress was regulated by both ethylene and auxin, with auxin signalling acting downstream of ethylene. Al‐induced PIN1 up‐regulation and auxin accumulation in the root‐apex TZ was also regulated by the calossin‐like protein BIG. Together, our results provide insight into how Al stress induces local auxin accumulation in the TZ and root‐growth inhibition through the local regulation of auxin transport.