title: Endophytic BacteriumPseudomonas fluorescensRG11 May Transform Tryptophan to Melatonin and Promote Endogenous Melatonin Levels in the Roots of Four Grape Cultivars.
abstract: Endophytes have been verified to synthesize melatoninin vitroand promote abiotic stress-induced production of endogenous melatonin in grape (Vitis viniferaL.) roots. This study aimed to further characterize the biotransformation of tryptophan to melatonin in the endophytic bacteriumPseudomonas fluorescensRG11 and to investigate its capacity for enhancing endogenous melatonin levels in the roots of different grape cultivars. Using ultra performance liquid chromatography-tandem mass spectrometry combined with 15N double-labeledL-tryptophan as the precursor for melatonin, we detected isotope-labeled 5-hydroxytryptophan, serotonin,N-acetylserotonin, and melatonin, but tryptamine was not detected during thein vitroincubation ofP. fluorescensRG11. Furthermore, the production capacity of these four compounds peaked during the exponential growth phase. RG11 colonization increased the endogenous levels of 5-hydroxytryptophan,N-acetylserotonin, and melatonin, but reduced those of tryptamine and serotonin, in the roots of the Red Globe grape cultivar under salt stress conditions. Quantitative real-time PCR revealed that RG11 reduced the transcription of grapevine tryptophan decarboxylase and serotoninN-acetyltransferase genes when compared to the un-inoculated control. These results correlated with decreased reactive oxygen species bursts and cell damage, which were alleviated by RG11 colonization under salt stress conditions. Additionally, RG11 promoted plant growth and enhanced the levels of endogenous melatonin in different grape cultivars. Intraspecific variation in the levels of melatonin precursors was found among four grape cultivars, and the associated root crude extracts appeared to significantly induce RG11 melatonin biosynthesisin vitro. Overall, this study provides useful information that enhances the existing knowledge of a potential melatonin synthesis pathway in rhizobacteria, and it reveals plant-rhizobacterium interactions that affect melatonin biosynthesis in plants subjected to abiotic stress conditions.
authors.affiliation: Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences Zhengzhou, China.
authors.forename: Yaner
authors.initials: Y
authors.lastname: Ma
authors.affiliation: Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural SciencesZhengzhou, China; College of Enology, Northwest A&F UniversityYangling, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Jiao
authors.affiliation: Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences Zhengzhou, China.
authors.forename: Xiucai
authors.initials: X
authors.lastname: Fan
authors.affiliation: Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences Zhengzhou, China.
authors.forename: Haisheng
authors.initials: H
authors.lastname: Sun
authors.affiliation: Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences Zhengzhou, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences Zhengzhou, China.
authors.forename: Jianfu
authors.initials: J
authors.lastname: Jiang
authors.affiliation: Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences Zhengzhou, China.
authors.forename: Chonghuai
authors.initials: C
authors.lastname: Liu
keywords: grapevine; melatonin; plant growth-promoting bacteria; root crude extracts; salt stress