3 research outputs found
Data_Sheet_1_SbbR/SbbA, an Important ArpA/AfsA-Like System, Regulates Milbemycin Production in Streptomyces bingchenggensis.docx
<p>Milbemycins, a group of 16-membered macrolide antibiotics, are used widely as insecticides and anthelmintics. Previously, a limited understanding of the transcriptional regulation of milbemycin biosynthesis has hampered efforts to enhance antibiotic production by engineering of regulatory genes. Here, a novel ArpA/AfsA-type system, SbbR/SbbA (SBI_08928/SBI_08929), has been identified to be involved in regulating milbemycin biosynthesis in the industrial strain S. bingchenggensis BC04. Inactivation of sbbR in BC04 resulted in markedly decreased production of milbemycin, while deletion of sbbA enhanced milbemycin production. Electrophoresis mobility shift assays (EMSAs) and DNase I footprinting studies showed that SbbR has a specific DNA-binding activity for the promoters of milR (the cluster-situated activator gene for milbemycin production) and the bidirectionally organized genes sbbR and sbbA. Transcriptional analysis suggested that SbbR directly activates the transcription of milR, while represses its own transcription and that of sbbA. Moreover, 11 novel targets of SbbR were additionally found, including seven regulatory genes located in secondary metabolite biosynthetic gene clusters (e.g., sbi_08420, sbi_08432, sbi_09158, sbi_00827, sbi_01376, sbi_09325, and sig24<sub>sbh</sub>) and four well-known global regulatory genes (e.g., glnR<sub>sbh</sub>, wblA<sub>sbh</sub>, atrA<sub>sbh</sub>, and mtrA/B<sub>sbh</sub>). These data suggest that SbbR is not only a direct activator of milbemycin production, but also a pleiotropic regulator that controls the expression of other cluster-situated regulatory genes and global regulatory genes. Overall, this study reveals the upper-layer regulatory system that controls milbemycin biosynthesis, which will not only expand our understanding of the complex regulation in milbemycin biosynthesis, but also provide a basis for an approach to improve milbemycin production via genetic manipulation of SbbR/SbbA system.</p
Substitution of a Single Amino Acid Reverses the Regiospecificity of the Baeyer–Villiger Monooxygenase PntE in the Biosynthesis of the Antibiotic Pentalenolactone
In
the biosynthesis of pentalenolactone (<b>1</b>), PenE
and PntE, orthologous proteins from <i>Streptomyces exfoliatus</i> and <i>S. arenae</i>, respectively, catalyze the flavin-dependent
Baeyer–Villiger oxidation of 1-deoxy-11-oxopentalenic acid
(<b>4</b>) to the lactone pentalenolactone D (<b>5</b>), in which the less-substituted methylene carbon has migrated. By
contrast, the paralogous PtlE enzyme from <i>S. avermitilis</i> catalyzes the oxidation of <b>4</b> to neopentalenolactone
D (<b>6</b>), in which the more substituted methane substitution
has undergone migration. We report the design and analysis of 13 single
and multiple mutants of PntE mutants to identify the key amino acids
that contribute to the regiospecificity of these two classes of Baeyer–Villiger
monooxygenases. The L185S mutation in PntE reversed the observed regiospecificity
of PntE such that all recombinant PntE mutants harboring this L185S
mutation acquired the characteristic regiospecificity of PtlE, catalyzing
the conversion of <b>4</b> to <b>6</b> as the major product.
The recombinant PntE mutant harboring R484L exhibited reduced regiospecificity,
generating a mixture of lactones containing more than 17% of <b>6</b>. These in vitro results were corroborated by analysis of
the complementation of the <i>S. avermitilis ΔptlED</i> double deletion mutant with <i>pntE</i> mutants, such
that <i>pntE</i> mutants harboring L185S produced <b>6</b> as the major product, whereas complemention of the <i>ΔptlED</i> deletion mutant with <i>pntE</i> mutants
carrying the R484L mutation gave <b>6</b> as more than 33% of
the total lactone product mixture
Novel Plant Growth Regulator Guvermectin from Plant Growth-Promoting Rhizobacteria Boosts Biomass and Grain Yield in Rice
Food is a fundamental human right, and global food security
is
threatened by crop production. Plant growth regulators (PGRs) play
an essential role in improving crop yield and quality, and this study
reports on a novel PGR, termed guvermectin (GV), isolated from plant
growth-promoting rhizobacteria, which can promote root and coleoptile
growth, tillering, and early maturing in rice. GV is a nucleoside
analogue like cytokinin (CK), but it was found that GV significantly
promoted root and hypocotyl growth, which is different from the function
of CK in Arabidopsis. The Arabidopsis CK receptor triple mutant ahk2-2 ahk3-3 cre1-12 still showed a GV response. Moreover, GV led different growth-promoting
traits from auxin, gibberellin (GA), and brassinosteroid (BR) in Arabidopsis and rice. The results from a four-year field
trial involving 28 rice varieties showed that seed-soaking treatment
with GV increased the yields by 6.2 to 19.6%, outperforming the 4.0
to 10.8% for CK, 1.6 to 16.9% for BR, and 2.2 to 7.1% for GA-auxin-BR
mixture. Transcriptome analysis demonstrated that GV induced different
transcriptome patterns from CK, auxin, BR, and GA, and SAUR genes may regulate GV-mediated plant growth and development. This
study suggests that GV represents a novel PGR with a unique signal
perception and transduction pathway in plants