Auxin synthesis in tea plant endophytic Herbaspirillum sp. ZXN111 and the plant growth promotion on Yunkang-10

Abstract:

[Objective] The predicted mechanism of indole-3-acetic acid (IAA) synthesis was investigated by molecular method on an endophytic bacterium Herbaspirillum aquaticum ZXN111 that was isolated from Zijuan tea. [Methods] Aromatic-amino-acid aminotransferase gene (tyrb) in indole-3-pyruvicacid (IPA) pathway responsible for IAA synthesis was selected on the basis of Herbaspirillum seropedicae genomic analytical results. Gene tyrb was mutated by recombinant plasmid pK19mobΩ2HMB-P-tyrb to produce mutant tyrb::pK19mobΩ2HMB, and a complementation strain tyrb::pK19mobΩ2HMB(+) was further constructed by recombinant plasmid pSRK-Gm-tyrb. IAA synthesis activities of mutant tyrb::pK19mobΩ2HMB, strain tyrb::pK19mobΩ2HMB(+) and wide type ZXN111 were analyzed, and the three strains' plant growth promotion (PGP) activity was evaluated by tissue cultured seedling of Yunkang-10. [Results] After tyrb gene mutated by pK19mobΩ2HMB-P-tyrb insertion, IAA synthetic activity of mutant tyrb::pK19mobΩ2HMB was much lower than that of wild-type ZXN111 in 48 h culture, but IAA synthesis activity of complementary strain tyrb::pK19mobΩ2HMB(+) was restored by plasmid pSRKGm-tyrb. The wide-type strain ZXN111 positively regulated the plant growth of Yunkang-10, while the mutant tyrb::pK19mobΩ2HMB lose the plant promotion activity significantly. [Conclusion] The indole-3-pyruvate (IPA) pathway is the primary IAA synthesis pathway in Herbaspirillum aquaticum ZXN111 and the tyrb is the key gene of IPA pathway, but other alternative pathways are also existed. Auxin production was one of the important contributors to PGP activity of Herbaspirillum aquaticum ZXN111.