AUTHOR=Zhang Hang , Liu Enliang , Huang Xinzheng , Kou Junfeng , Teng Dong , Lv Beibei , Han Xiaoqiang , Zhang Yongjun 

TITLE=Characterization of a Novel Insect-Induced Sesquiterpene Synthase GbTPS1 Based on the Transcriptome of Gossypium barbadense Feeding by Cotton Bollworm

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.898541

DOI=10.3389/fpls.2022.898541

ISSN=1664-462X

ABSTRACT=<p>When attacked by insect herbivores, plants initiate sophisticated defenses mediated by complex signaling networks and usually release a blend of functional volatiles such as terpenes against infestation. The extra-long staple cotton <italic>Gossypium barbadense</italic> cultivated worldwide as natural textile fiber crop is frequently exposed to a variety of herbivores, such as cotton bollworm <italic>Helicoverpa armigera</italic>. However, little is known about insect-induced transcriptional changes and molecular mechanisms underlying subsequent defense responses in <italic>G. barbadense</italic>. In the current study, transcriptome changes in <italic>G. barbadense</italic> infested with chewing <italic>H. armigera</italic> larvae were investigated, and we identified 5,629 differentially expressed genes (DEGs) in the infested cotton leaves compared with non-infested controls. <italic>H. armigera</italic> feeding triggered complex signaling networks in which almost all (88 out of 90) DEGs associated with the jasmonic acid (JA) pathway were upregulated, highlighting a central role for JA in the defense responses of <italic>G. barbadense</italic> against target insects. All DEGs involved in growth-related photosynthesis were downregulated, whereas most DEGs associated with defense-related transcript factors and volatile secondary metabolism were upregulated. It was noteworthy that a terpene synthase gene in the transcriptome data, <italic>GbTPS1</italic>, was strongly expressed in <italic>H. armigera</italic>-infested <italic>G. barbadense</italic> leaves. The upregulation of <italic>GbTPS1</italic> in qPCR analysis also suggested an important role for <italic>GbTPS1</italic> in herbivore-induced cotton defense. <italic>In vitro</italic> assays showed that recombinant GbTPS1 catalyzed farnesyl pyrophosphate and neryl diphosphate to produce three sesquiterpenes (selinene, α-gurjunene, and β-elemene) and one monoterpene (limonene), respectively. Moreover, these catalytic products of GbTPS1 were significantly elevated in <italic>G. barbadense</italic> leaves after <italic>H. armigera</italic> infestation, and elemene and limonene had repellent effects on <italic>H. armigera</italic> larvae in a dual-choice bioassay and increased larval mortality in a no-choice bioassay. These findings provide a valuable insight into understanding the transcriptional changes reprogramming herbivore-induced sesquiterpene biosynthesis in <italic>G. barbadense</italic> infested by <italic>H. armigera</italic>, which help elucidate the molecular mechanisms underlying plant defense against insect pests.</p>