| Stress is an important environmental factor limiting productivity of plants,especially fast growing species with high water consumption like poplar.Abscisic acid(ABA)is a phytohormone that positively regulates seed dormancy and drought tolerance.The pyrabactin resistance-like(PYL)ABA receptor family has been identified and widely characterized in Arabidopsis thaliana.However,their functions in poplars remain unknown.Here,we report that 2 of 14 PYRL ortholognes in poplar(Populus trichocarpa)(PtPYRLs)function as a positive regulator of the ABA signal transduction pathway.The Arabidopsis transient expression and yeast two-hybrid assays showed the interaction among PtPYRL1 and PtPYRL5,a clade A protein phosphatase 2C,and a SnRK2,suggesting that a core signalling complex for ABA signaling pathway exists in poplars.Phenotypic analysis of PtPYRL1 and PtPYRL5 transgenic Arabidopsis showed that these two genes positively regulated the ABA response during the seed germination.More importantly,the overexpression of PtPYRL1 and PtPYRL5 substantially improved ABA sensitivity and drought stress tolerance in transgenic plants.In summary,we comprehensively uncovered the properties of PtPYRL1 and PtPYRL5,which may be good target genes to genetically engineer drought-tolerant plants.The importance of ABA signaling mediated by ABA receptor genes to plant drought resistance has been underlined by experiments in which constitutive overexpression of different ABA receptor genes can greatly increase drought resistance in a range of plant.Poplar is one of the most important timber tree species planted in China,however,the most of them belong to non-resistance varieties.Therefore,the study and practice to improve the quality of poplar resistance have important practical significance to the environment protection and the progress of our society and the economy.Overexpression of ABA receptor genes have been reported to increase the drought resistance of various herbaceous or shrub species,but very little is known about the role of these ABA receptors in the resistance of trees.Firstly,we determined the relative expression level of all of poplar potential ABA receptor genes under different conditions associated with ABA signal(including ABA,drought and low temperature),we found that in the case of ABA treatment,the relative expression level of most of these genes(including PtPYRL1 and PtPYRL5)was down-regulated,this result was similar to the situations of Arabidopsis ABA receptor genes with ABA treatment.However,the relative expression level of most of these genes(including PtPYRL1 and PtPYRL5)was up-regulated under drought and low temperature treatment.Interestingly,with continuous low temperature treatment,the relative expression level of most of these genes was down-regulated.To improve the hybrid poplar Populus davidiana ×Populus bolleana stress resistance,successful Agrobacterium-mediated transformation of PtPYRLl or PtPYRL5 to the shoot stem explants of Populus davidiana × Populus bolleana and regeneration of transgenic plants has been performed.In order to elucidate mechanism of overexpressing the PtPYRLl or PtPYRL5 gene response to abiotic stress in woody plants,the wild-type plants(WT)(Populus davidiana × Populus bolleana)and its transgenic varieties that overexpress the PtPYRL1 or PtPYRL5 gene were investigated to identify their growth and physiological character responses to abiotic stress.The stress contained the drought,high osmotic potential and chilling injury in a laboratory environment with artificial conditions.The indicator to judge the stress resistance include shoot weight,shoot length,water potential,proline accumulation,MDA formation,trypan blue and DAB staining that show H2O2 formation.The ultimate goal is to trying to get strong resistance of poplar clones,and to provide a theoretical basis and practical guidance for the promotion of this transgenic poplar production,in a bid to generate greater economic,environmental and social benefits. |
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