茶树内生草螺菌ZXN111生长素合成及其对云抗-10号植物的促生功能

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

摘要:

[目的] 以紫娟茶树分离的内生菌水生草螺菌ZXN111为研究对象，通过分子遗传学方法证实该菌株植物生长素吲哚3-乙酸（IAA）合成的主要分子途径。[方法] 参考草螺菌基因组信息中IAA合成基因簇，选取与IAA合成密切相关的候选基因，即芳香族氨基酸转氨酶基因（tyrb），通过基因插入突变与基因互补方法，结合茶树组培苗体内促生能力分析，初步验证水生草螺菌生长素合成的主要机制。[结果] 植物生长素IAA合成候选基因tyrb突变后，突变株tyrb：：pK19mobΩ2HMB 48 h的IAA合成量显著低于野生型菌株ZXN111，且tyrb基因互补后，互补株tyrb：：pK19mobΩ2HMB（+）的IAA合成能力得到了显著恢复。茶树促生实验发现，突变株tyrb：：pK19mobΩ2HMB接种组的茶树组培苗根长、根重及植株鲜重指标上均显著低于野生菌处理组。[结论] 水生草螺菌ZXN111有多条IAA合成途径，其中的吲哚-3-丙酮酸（IPA）是最主要途径，其生长素合成对寄主茶树具有显著的促生功能。

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.