Transcriptional Regulator PhlH Modulates 2,4-Diacetylphloroglucinol Biosynthesis in Response to the Biosynthetic Intermediate and End Product
Transcriptional Regulator PhlH Modulates 2,4-Diacetylphloroglucinol Biosynthesis in Response to the Biosynthetic Intermediate and End Product
复制标题
转录调节剂 PhlH 调节 2,4-二乙酰基间苯三酚生物合成以响应生物合成中间体和最终产物
DOI：
10.1128/aem.01419-17
复制
发表时间：
2017-11-01
影响因子：
4.4
通讯作者：
He, Yong-Xing
中科院分区：
文献类型：
--
作者：
Yan, Xu;Yang, Rui;He, Yong-Xing
摘要荧光假单胞菌产生的次生代谢产物2，4-二乙酰基间苯三酚（2，4-DAPG）可拮抗根际土传植物病原菌。负责2，4-DAPG生物合成的基因簇被命名为phlACBDEFGH，并且仍然不清楚该基因簇内的途径特异性调节剂phlH如何调节2，4-DAPG的代谢。在这里，我们发现荧光假单胞菌菌株2 P2, 4中的PhlH通过结合与σ70因子识别的−35位点重叠的序列基序来抑制编码2，4-DAPG水解酶的phlG基因的表达。通过PhlH配体的生化筛选，我们鉴定了终产物2，4-DAPG及其生物合成中间体单乙酰基间苯三酚（MAPG），其可以作为信号分子调节PhlH与靶序列的结合并激活phlG的表达。比较ΔphlH、ΔphlG和ΔphlHG突变体之间的2，4-DAPG产量证实了phlH和phlG对2，4-DAPG生物合成施加负反馈调节。进一步证明，PhlG催化的2，4-DAPG降解在2，4-DAPG耐受性中起不显著的作用，但有助于在碳/氮饥饿条件下的细菌生长优势。总之，我们的数据表明，通过监测和下调原位水平的2，4-DAPG，phlHG基因可以动态地调节代谢负荷归因于2，4-DAPG的生产和潜在的根际适应。重要性2，4-DAPG是由生防假单胞菌合成的广谱抗生素，对细菌、真菌、卵菌和线虫具有广谱抗菌作用，在抑制土传植物病原菌方面发挥重要作用。虽然2，4-DAPG生物合成基因簇（phl）中的大多数基因已经被表征，但是仍然不清楚途径特异性调节因子phlH如何参与2，4-DAPG代谢。这项工作揭示了PhlH在调节2，4-DAPG水平中的作用，其通过响应2，4-DAPG和MAPG而控制2，4-DAPG水解酶PhlG的表达。由于2，4-DAPG生物合成对生物防治假单胞菌施加代谢负荷，因此预期PhlH对phlG的精细调节提供了一种动态调节归因于2，4-DAPG产生的代谢负荷的方法。
ABSTRACT Certain strains of biocontrol bacterium Pseudomonas fluorescens produce the secondary metabolite 2,4-diacetylphloroglucinol (2,4-DAPG) to antagonize soilborne phytopathogens in the rhizosphere. The gene cluster responsible for the biosynthesis of 2,4-DAPG is named phlACBDEFGH and it is still unclear how the pathway-specific regulator phlH within this gene cluster regulates the metabolism of 2,4-DAPG. Here, we found that PhlH in Pseudomonas fluorescens strain 2P24 represses the expression of the phlG gene encoding the 2,4-DAPG hydrolase by binding to a sequence motif overlapping with the −35 site recognized by σ70 factors. Through biochemical screening of PhlH ligands we identified the end product 2,4-DAPG and its biosynthetic intermediate monoacetylphloroglucinol (MAPG), which can act as signaling molecules to modulate the binding of PhlH to the target sequence and activate the expression of phlG. Comparison of 2,4-DAPG production between the ΔphlH, ΔphlG, and ΔphlHG mutants confirmed that phlH and phlG impose negative feedback regulation over 2,4-DAPG biosynthesis. It was further demonstrated that the 2,4-DAPG degradation catalyzed by PhlG plays an insignificant role in 2,4-DAPG tolerance but contributes to bacterial growth advantages under carbon/nitrogen starvation conditions. Taken together, our data suggest that by monitoring and down-tuning in situ levels of 2,4-DAPG, the phlHG genes could dynamically modulate the metabolic loads attributed to 2,4-DAPG production and potentially contribute to rhizosphere adaptation. IMPORTANCE 2,4-DAPG, which is synthesized by biocontrol pseudomonad bacteria, is a broad-spectrum antibiotic against bacteria, fungi, oomycetes, and nematodes and plays an important role in suppressing soilborne plant pathogens. Although most of the genes in the 2,4-DAPG biosynthetic gene cluster (phl) have been characterized, it is still not clear how the pathway-specific regulator phlH is involved in 2,4-DAPG metabolism. This work revealed the role of PhlH in modulating 2,4-DAPG levels by controlling the expression of 2,4-DAPG hydrolase PhlG in response to 2,4-DAPG and MAPG. Since 2,4-DAPG biosynthesis imposes a metabolic burden on biocontrol pseudomonads, it is expected that the fine regulation of phlG by PhlH offers a way to dynamically modulate the metabolic loads attributed to 2,4-DAPG production.