Functional analysis of the 1-aminocyclopropane-1-carboxylate deaminase gene of the biocontrol fungus Trichoderma asperellum ACCC30536

Abstract

1-aminocyclopropane-1-carboxylate (ACC) deaminase (ACCD) cleaves ACC, the immediate precursor of the ethylene, decreasing the level of ethylene and inhibition of plant growth resulted by environmental stresses. Here, TaACCD was cloned from the biocontrol agent Trichoderma asperellum ACCC30536. Its open reading frame was 1047 bp long encoding a 37 kD protein of 348 aa, and a pI of 5.77. Phylogenetic analysis demonstrated this protein to be closely related to ACCD from T. asperellum T203 (ACX94231). Transformation of Populus davidiana × P. bolleana with TaACCD, increased salinity tolerance of transgenic plants Pdb-ACCD3 and Pdb-ACCD5. Transgenic plants could survive at salinity of 200 mM NaCl, whereas untransformed control poplar Pdb-NT could withstand salinity to 150 mM NaCl. Transformed plants accumulated higher amounts of chlorophyll compared to Pdb-NT plants. Accumulation of reactive oxygen species (ROS) was regulated by TaACCD under salt stress, as shown from higher superoxide dismutase (SOD) and peroxidase (POD) activities, as well as NBT and DAB staining. Evans blue staining showed that TaACCD maintained membrane integrity in Populus under salt stress conditions. Additionally, TaACCD expression decreased ethylene content of transgenic plants compared to nontransgenic plants, but salt content in plant leaves didnt show obvious difference under same salt concentration. To the best of our knowledge, the current study is the first demonstration that the TaACCD gene from T. asperellum ACCC30536 can enhance tolerance of Populus to salt stress.