Abstract
Burkholderia pyrrocinia JK-SH007 is a plant growth-promoting bacteria (PGPB), that can promote the growth of poplar and other trees, and, production of the plant hormone indole-3-acetic acid (IAA) is one of the reasons for this effect. Therefore, the aims of this study were to evaluate the effect of the external environment on the synthesis of IAA by B. pyrrocinia JK-SH007 and to perform a functional analysis of its IAA synthesis pathway. In this study, IAA and its synthetic intermediates indole-3-acetamide (IAM), indole-3-pyruvic acid (IPyA), tryptamine (TAM), and indole-3-acetonitrile (IAN) were detected in B. pyrrocinia JK-SH007 fermentation broth by high-performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS), and these indolic compounds were also found in the cell-free extraction of B. pyrrocinia JK-SH007, but the genomic analysis of B. pyrrocinia JK-SH007 indicated that IAA biosynthesis was mainly through the IAM and TAM pathways. The effects of L-tryptophan (L-Trp), temperature and pH on the synthesis of IAA were investigated, and the results showed that L-Trp exerted a significant effect on IAA synthesis and that 37°C and pH 7 were the optimal conditions IAA production by B. pyrrocinia JK-SH007. In addition, the protein expression of tryptophan 2-monooxygenase and indoleacetamide hydrolase, which are the key enzymes of the indole acetamide-mediated IAA synthesis pathway, was analyzed, and their activity was verified by substrate feeding experiments. The results revealed the existence of an IAA synthesis pathway mediated by IAM and indicated that this pathway plays a role in B. pyrrocinia JK-SH007. This study lays the foundation for further exploration of the specific pathway and mechanism of IAA synthesis in B. pyrrocinia JK-SH007.
Highlights
Plant growth-promoting bacteria (PGPB), which are ubiquitous in plants (Strobel et al, 2004), can help host plants absorb nutrients and improve their plant growth (Strobel et al, 2004; Santoyo et al, 2016)
Indole-3-acetic acid (Supplementary Figures S1A,C) and its synthetic intermediate, IAM (Supplementary Figures S1B,D), were detected in B. pyrrocinia JK-SH007 fermentation broth by HPLC-MS/MS analysis, were detected in B. pyrrocinia JK-SH007 fermentation broth by HPLC-MS/MS analysis (Supplementary Figures S1C,D), which indicates that B. pyrrocinia JK-SH007 has the ability to synthesize indole-3-acetic acid (IAA) and that might harbor an IAM-mediated IAA synthesis pathway
The ability of B. pyrrocinia JK-SH007 to synthesize the auxin IAA was confirmed by HPLC-MS/MS, and the related IAA synthetic intermediates were detected, IAA, and its synthetic intermediates were found in the cell-free extraction of B. pyrrocinia JK-SH007, but the genomic analysis of B. pyrrocinia JK-SH007 indicated that IAA biosynthesis was mainly through the IAM and TAM pathways
Summary
Plant growth-promoting bacteria (PGPB), which are ubiquitous in plants (Strobel et al, 2004), can help host plants absorb nutrients and improve their plant growth (Strobel et al, 2004; Santoyo et al, 2016). The tryptophan-dependent pathways include the indole-3-acetamide (IAM), indole-3-pyruvic acid (IPyA), indole-3-acetonitrile (IAN), tryptamine (TAM), and tryptophan side-chain oxidase (TSO) pathways (Duca et al, 2014; Di et al, 2016), and the IAM pathway is one of the IAA synthesis pathways in which L-tryptophan (L-Trp) is a precursor. In this pathway, L-Trp is first converted into IAM by tryptophan 2monooxygenase, which is encoded by the iaaM gene, and IAM is further catalyzed by indoleacetamide hydrolase, which is encoded by the iaaH gene, to synthesize IAA (Di et al, 2016). The IAM pathway is thought to exist in both phytopathogenic and beneficial bacteria (Gudrun et al, 1984; Theunis et al, 2004)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
