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Background: Azadirachtin A is a triterpenoid from neem tree exhibiting excellent activities against over 600 insect species in agriculture. The production of azadirachtin A depends on extraction from neem tissues, which is not an eco-friendly and sustainable process. The low yield and discontinuous supply of azadirachtin A impedes further applications. The biosynthetic pathway of azadirachtin A is still unknown and is the focus of our study. Results: We attempted to explore azadirachtin A biosynthetic pathway and identified the key genes involved by analyzing transcriptome data from five neem tissues through the hybrid-sequencing (Illumina HiSeq and Pacific Biosciences Single Molecule Real-Time (SMRT)) approach. Candidates were first screened by comparing the expression levels between the five tissues. After phylogenetic analysis, domain prediction, and molecular docking studies, 22 candidates encoding 2,3-oxidosqualene cyclase (OSC), alcohol dehydrogenase, cytochrome P450 (CYP450), acyltransferase, and esterase were proposed to be potential genes involved in azadirachtin A biosynthesis. Among them, two unigenes encoding homologs of MaOSC1 and MaCYP71CD2 were identified. A unigene encoding the complete homolog of MaCYP71BQ5 was reported. Accuracy of the assembly was verified by quantitative real-time PCR (qRT-PCR) and full-length PCR cloning. Conclusions: By integrating and analyzing transcriptome data from hybrid-seq technology, 22 differentially expressed genes (DEGs) were finally selected as candidates involved in azadirachtin A pathway. The obtained reliable and accurate sequencing data provided important novel information for understanding neem genome. Our data shed new light on understanding the biosynthesis of other triterpenoids in neem trees and provides a reference for exploring other valuable natural product biosynthesis in plants.

Background: Azadirachtin A is a triterpenoid from neem tree exhibiting excellent activities against over 600 insect species in agriculture. The manufacture of azadirachtin A depends on extraction from neem tissues, which is not ecofriendly and sustainable. The low yield and discontinuous supply impeded the further application. The biosynthetic pathway of azadirachtin A is still unknown. Results: We attempted to explore azadirachtin A biosynthetic pathway and identified key involved genes by analyzing transcriptome data of five neem tissues through hybrid-seq (Illumina HiSeq and Pacific Biosciences Single Molecule Real Time (PacBio SMRT)) approach. Candidates were firstly screened by comparing expression level within five tissues. After phylogenetic analysis, domain prediction and molecular docking, 22 candidates encoding 2,3-oxidosqualene cyclase (OSC), alcohol dehydrogenase (ADH), cytochrome P450 (CYP450), acyltransferase (ACT) and esterase (EST) were proposed to be potential genes involved in azadirachtin A biosynthesis. Among them, two unigenes encoding homolog of MaOCS1 and MaCYP71CD2 were identified. An unigene encoding complete homolog of MaCYP71BQ5 was first reported. Accuracy of the assemblies were verified by Quantitative Real-Time PCR (qRT-PCR) and full-length cloning PCR. Conclusions: By integrating and analysis transcriptome data from hybrid-seq technology, 22 DEGs were finally selected as candidates involved in azadirachtin A pathway. The obtained reliable and accurate sequencing data provided important novel information for understanding neem genome. Our data shed new light on the understanding of other triterpenoids biosynthesis in neem trees and provide reference for exploring other valuable natural product biosynthesis in plants.

A growing accumulation of plastic wastes has become a severe environmental and social issue. It is urgent to develop innovative approaches for the disposal of plastic wastes. In recent years, reports on biodegradation of synthetic plastics by microorganisms or enzymes have sprung up, and these offer a possibility to develop biological treatment technology for plastic wastes. In this review, we have comprehensively summarized the microorganisms and enzymes that are able to degrade a variety of generally used synthetic plastics, such as polyethylene (PE), polystyrene (PS), polypropylene (PP), polyvinyl chloride (PVC), polyurethane (PUR), and polyethylene terephthalate (PET). In addition, we have highlighted the microbial metabolic pathways for plastic depolymerization products and the current attempts toward utilization of such products as feedstocks for microbial production of chemicals with high value. Taken together, these findings will contribute to building a conception of bio-upcycling plastic wastes by connecting the biodegradation of plastic wastes to the biosynthesis of valuable chemicals in microorganisms. Last, but not least, we have discussed the challenges toward microbial degradation and valorization of plastic wastes.

Additional file 14 Figure S1. The workflow of gene mining. Letters L, F, R, S, and f represent leaf, fruit, root, stem, and flower, respectively.

Additional file 15 Figure S2. Quantitative Real-Time PCR (qRT-PCR) validation of selected unigenes from fruit, leaf, root, stem, and flower tissues of A. indica. The relative expression level of each selected gene was determined by the 2−ΔΔCT method. Experiments were conducted in triplicates.

Additional file 17 Figure S4. The amino acid sequence alignment of transcript/16742, AiCYP71BQ5, and MaCYP71BQ5. Same amino acids are shown in white with red background.

Additional file 16 Figure S3. The alignment result of transcript/14449 and AiOSC1. Sequence marked with “*” represents the transcript/14449 from our data.

Plastic pollution has become a global environmental issue, making it necessary to explore the environmental disposal technology for plastic waste. Recently, we and other researchers have individually found microorganisms or enzymes from nature that can degrade synthetic plastic. These findings indicated that the capability of these microorganisms or enzymes to degrade plastic could be used for the disposal of plastic waste. Polyurethane (PUR) was one of the most used general plastic and its plastic waste occupied 30% of the total volume of different plastic waste. This review tried to provide a comprehensive summary of the researches on microbial degradation of PUR plastic in the past 70 years since its invention, and focused on the PUR-degrading fungi, bacteria, genes or enzymes, degradation products and the corresponding biological disposal technologies. We finally proposed the key scientific challenges on the development of high efficient biological disposal for PUR waste in the perspective researches.未被合理处置的废塑料污染已成为全球性的环境问题，探索塑料废弃物的无害化处理技术势在必行。近来，研究证实了自然界中存在可以降解塑料的微生物及酶。利用微生物或酶对废塑料进行生物处理成为可能。聚氨酯塑料 (Polyurethane, PUR) 是广泛应用的通用塑料之一，其废弃物量已占到所有废塑料总体积的30%。文中将PUR 塑料发明应用70 年来有关微生物降解的研究进行了全面综述，对PUR 塑料降解真菌、细菌、降解基因与酶、降解产物及相关的生物处理技术系统等进行了总结与分析，并对实现PUR 废塑料高效生物处理需解决的关键科学问题进行了展望。.