Mechanisms by which beneficial rhizobacteria promote plant growth include tryptophan-dependent indole-3-acetic acid (IAA) synthesis. The abundance of tryptophan in the rhizosphere, however, may influence the level of benefit provided by IAA-producing rhizobacteria. This study examined the cucumber-Bacillus amyloliquefaciens SQR9 system and found that SQR9, a bacterium previously shown to enhance the growth of cucumber, increased root secretion of tryptophan by three- to fourfold. Using a split-root system, SQR9 colonization of roots in one chamber not only increased tryptophan secretion from the noninoculated roots but also increased the expression of the cucumber tryptophan transport gene but not the anthranilate synthesis gene in those roots. The increased tryptophan in isolated rhizosphere exudates was sufficient to support increased IAA production by SQR9. Moreover, SQR9 colonization of roots in one chamber in the split-root system resulted in sufficient tryptophan production by the other roots to upregulate SQR9 IAA biosynthesis genes, including a 27-fold increase in the indole-3-acetonitrilase gene yhcX during subsequent colonization of those roots. Deletion of yhcX eliminated SQR9-mediated increases in root surface area, likely by reducing IAA-stimulated lateral root growth. This study demonstrates a chemical dialogue between B. amyloliquefaciens and cucumber in which this communication contributes to bacteria-mediated plant-growth enhancement.

No abstract

The phytohormone indole‐3‐acetic acid (IAA) has been demonstrated to contribute to the plant growth‐promoting effect of rhizobacteria, but the IAA biosynthesis pathway in rhizobacteria remains unclear. The ysnE gene, encoding a putative tryptophan acetyltransferase, has been demonstrated to be involved in and strongly contribute to IAA production in Bacillus, but the mechanism is unknown. In this study, to investigate how ysnE participates in IAA biosynthesis in the plant growth‐promoting rhizobacterium Bacillus amyloliquefaciens SQR9, differences in the produced IAA biosynthesis intermediates between wild‐type SQR9 and ΔysnE were analyzed and compared, and the effects of different intermediate compounds on the production of IAA and the accumulation of other intermediates were also investigated. The results showed that the mutant ΔysnE produced more indole‐3‐lactic acid (ILA) and tryptamine (TAM) than the SQR9 wild‐type strain (nearly 1.6‐ and 2.1‐fold), while the production of tryptophol (TOL) was significantly decreased by 46%. When indole‐3‐pyruvic acid (IPA) served as the substrate, the concentration of ILA in the ΔysnE fermentation broth was much higher than that of the wild type, while IAA and TOL were significantly lower, and ΔysnE was lower than SQR9 in IAA and TOL with the addition of TAM. The TOL content in the ΔysnE fermentation broth was much lower than that in the wild‐type SQR9 with the addition of ILA. We suggest that ysnE may be involved in the IPA and TAM pathways and play roles in indole acetaldehyde (IAAld) synthesis from IPA and TAM and in the conversion of ILA to TOL.

No abstract

In this paper, we introduce the two-sided fractional quaternion Fourier transform (FrQFT) and give some properties of it. The main results of this paper are divided into three parts. Firstly we give a definition of the FrQFT. Secondly based on properties of the two-sided QFT, we study the relationship between the two-sided QFT and the two-sided FrQFT, and give some differential properties of the two-sided FrQFT and the Parseval identity. Finally, we give an example to illustrate the application of the two-sided FrQFT and its inverse transform in solving partial differential equations.