Multi-tissue transcriptome analysis using hybrid-seq revealed potential genes and biological pathways associated with azadirachtin A biosynthesis in neem (Azadirachtin indica)

Abstract

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.