Engineering Nicotiana tabacum for the de novo biosynthesis of DMNT to regulate orientation behavior of the parasitoid wasps Microplitis mediator

Pangenome Identification and Analysis of Terpene Synthase Gene Family Members in Gossypium

Terpene synthases (TPSs), key gatekeepers in the biosynthesis of herbivore-induced terpenes, are pivotal in the diversity of terpene chemotypes across and within plant species. Here, we constructed a gene-based pangenome of the Gossypium genus by integrating the genomes of 17 diploid and 10 tetraploid species. Within this pangenome, 208 TPS syntelog groups (SGs) were identified, comprising 2 core SGs (TPS5 and TPS42) present in all 27 analyzed genomes, 6 softcore SGs (TPS11, TPS12, TPS13, TPS35, TPS37, and TPS47) found in 25 to 26 genomes, 131 dispensable SGs identified in 2 to 24 genomes, and 69 private SGs exclusive to a single genome. The mutational load analysis of these identified TPS genes across 216 cotton accessions revealed a great number of splicing variants and complex splicing patterns. The nonsynonymous/synonymous Ka/Ks value for all 52 analyzed TPS SGs was less than one, indicating that these genes were subject to purifying selection. Of 208 TPS SGs encompassing 1795 genes, 362 genes derived from 102 SGs were identified as atypical and truncated. The structural analysis of TPS genes revealed that gene truncation is a major mechanism contributing to the formation of atypical genes. An integrated analysis of three RNA-seq datasets from cotton plants subjected to herbivore infestation highlighted nine upregulated TPSs, which included six previously characterized TPSs in G. hirsutum (AD1_TPS10, AD1_TPS12, AD1_TPS40, AD1_TPS42, AD1_TPS89, and AD1_TPS104), two private TPSs (AD1_TPS100 and AD2_TPS125), and one atypical TPS (AD2_TPS41). Also, a TPS-associated coexpression module of eight genes involved in the terpenoid biosynthesis pathway was identified in the transcriptomic data of herbivore-infested G. hirsutum. These findings will help us understand the contributions of TPS family members to interspecific terpene chemotypes within Gossypium and offer valuable resources for breeding insect-resistant cotton cultivars.

Engineering DMNT emission in cotton enhances direct and indirect defense against mirid bugs

INTRODUCTION

As an important herbivore-induced plant volatile, (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) is known for its defensive role against multiple insect pests, including attracting natural enemies. A terpene synthase (GhTPS14) and two cytochrome P450 (GhCYP82L1, GhCYP82L2) enzymes are involved in the de novo synthesis of DMNT in cotton. We conducted a study to test the potential of manipulating DMNT-synthesizing enzymes to enhance plant resistance to insects.

OBJECTIVES

To manipulate DMNT emissions in cotton and generate cotton lines with increased resistance to mirid bug Apolygus lucorum.

METHODS

Biosynthesis and emission of DMNT by cotton plants were altered using CRISPR/Cas9 and overexpression approaches. Dynamic headspace sampling and GC-MS analysis were used to collect, identify and quantify volatiles. The attractiveness and suitability of cotton lines against mirid bug and its parasitoid Peristenus spretus were evaluated through various assays.

RESULTS

No DMNT emission was detected in knockout CAS-L1L2 line, where both GhCYP82L1 and GhCYP82L2 were knocked out. In contrast, gene-overexpressed lines released higher amounts of DMNT when infested by A. lucorum. At the flowering stage, L114 (co-overexpressing GhCYP82L1 and GhTPS14) emitted 10-15-fold higher amounts than controls. DMNT emission in overexpressed transgenic lines could be triggered by methyl jasmonate (MeJA) treatment. Apolygus lucorum and its parasitoid were far less attracted to the double edited CAS-L1L2 plants, however, co-overexpressed line L114 significantly attracted bugs and female wasps. A high dose of DMNT, comparable to the emission of L114, significantly inhibited the growth of A. lucorum, and further resulted in higher mortalities.

CONCLUSION

Turning down DMNT emission attenuated the behavioral preferences of A. lucorum to cotton. Genetically modified cotton plants with elevated DMNT emission not only recruited parasitoids to enhance indirect defense, but also formed an ecological trap to kill the bugs. Therefore, manipulation of DMNT biosynthesis and emission in plants presents a promising strategy for controlling mirid bugs.

The microbial biosynthesis of noncanonical terpenoids

Terpenoids are a class of structurally complex, naturally occurring compounds found predominantly in plant, animal, and microorganism secondary metabolites. Classical terpenoids typically have carbon atoms in multiples of five and follow well-defined carbon skeletons, whereas noncanonical terpenoids deviate from these patterns. These noncanonical terpenoids often result from the methyltransferase-catalyzed methylation modification of substrate units, leading to irregular carbon skeletons. In this comprehensive review, various activities and applications of these noncanonical terpenes have been summarized. Importantly, the review delves into the biosynthetic pathways of noncanonical terpenes, including those with C6, C7, C11, C12, and C16 carbon skeletons, in bacteria and fungi host. It also covers noncanonical triterpenes synthesized from non-squalene substrates and nortriterpenes in Ganoderma lucidum, providing detailed examples to elucidate the intricate biosynthetic processes involved. Finally, the review outlines the potential future applications of noncanonical terpenoids. In conclusion, the insights gathered from this review provide a reference for understanding the biosynthesis of these noncanonical terpenes and pave the way for the discovery of additional unique and novel noncanonical terpenes. KEY POINTS: •The activities and applications of noncanonical terpenoids are introduced. •The noncanonical terpenoids with irregular carbon skeletons are presented. •The microbial biosynthesis of noncanonical terpenoids is summarized.

Stemborer-induced rice plant volatiles boost direct and indirect resistance in neighboring plants

Herbivore-induced plant volatiles (HIPVs) are known to be perceived by neighboring plants, resulting in induction or priming of chemical defenses. There is little information on the defense responses that are triggered by these plant-plant interactions, and the phenomenon has rarely been studied in rice. Using chemical and molecular analyses in combination with insect behavioral and performance experiments, we studied how volatiles emitted by rice plants infested by the striped stemborer (SSB) Chilo suppressalis affect defenses against this pest in conspecific plants. Compared with rice plants exposed to the volatiles from uninfested plants, plants exposed to SSB-induced volatiles showed enhanced direct and indirect resistance to SSB. When subjected to caterpillar damage, the HIPV-exposed plants showed increased expression of jasmonic acid (JA) signaling genes, resulting in JA accumulation and higher levels of defensive proteinase inhibitors. Moreover, plants exposed to SSB-induced volatiles emitted larger amounts of inducible volatiles and were more attractive to the parasitoid Cotesia chilonis. By unraveling the factors involved in HIPV-mediated defense priming in rice, we reveal a key defensive role for proteinase inhibitors. These findings pave the way for novel rice management strategies to enhance the plant's resistance to one of its most devastating pests.

Characterization of trans-Nerolidol Synthase from Celastrus angulatus Maxim and Production of trans-Nerolidol in Engineered Saccharomyces cerevisiae

Volatile terpenoids are a large group of important secondary metabolites and possess many biological activities. The acyclic sesquiterpene trans-nerolidol is one of the typical representatives and widely used in cosmetics and agriculture. Here, the accumulation of volatile terpenes in different tissues of Celastrus angulatus was investigated, and two trans-nerolidol synthases, CaNES1 and CaNES2, were identified and characterized by in vitro enzymatic assays. Both genes are differentially transcribed in different tissues of C. angulatus. Next, we constructed a Saccharomyces cerevisiae cell factory to enable high-level production of trans-nerolidol. Glucose was the sole carbon source to sequentially control gene expression between the competitive squalene and trans-nerolidol pathways. Finally, the trans-nerolidol production of recombinant strain LWG003-CaNES2 was 7.01 g/L by fed-batch fermentation in a 5 L bioreactor. The results clarify volatile terpenoid biosynthesis in C. angulatus and provide a promising potential for industrial production of trans-nerolidol in S. cerevisiae.