Project description:Herbivorous insects use plant volatile compounds to find their host plants for feeding and egg deposition. The monophagous beetle Agasicles hygrophila uses a volatile (E)-4,8-dimethyl-1,3,7-nonanetriene (DMNT) to recognize its host plant Alternanthera philoxeroides. Alternanthera philoxeroides releases DMNT in response to A. hygrophila attack and nerolidol synthase (NES) is a key enzyme in DMNT biosynthesis; however, the effect of A. hygrophila on NES expression remains unclear. In this study, the A. philoxeroides transcriptome was sequenced and six putative NES genes belonging to the terpene synthase-g family were characterized. The expression of these NES genes was assayed at different times following A. hygrophila contact, feeding or mechanical wounding. Results showed that A. hygrophila contact and feeding induced NES expression more rapidly and more intensely than mechanical wounding alone. This may account for a large release of DMNT following A. hygrophila feeding in a previous study and subsequently facilitate A. hygrophila to find host plants. Our research provides a powerful genetic platform for studying invasive plants and lays the foundation for further elucidating the molecular mechanisms of the interaction between A. philoxeroides and its specialist A. hygrophila.
Project description:Alternanthera philoxeroides is a perennial amphibious weed native to South America but has now spread to diverse parts of the world. A. philoxeroides reproduces both sexually and asexually in its native range, but propagates solely through vegetative means in its introduced range. Traits associated with sexual reproduction become degraded for sexual dysfunction, with flowers possessing either pistillate stamens or male-sterile anthers. Degradations of sexual characters for loss of sexuality commonly take place in clonal plants. The underlying molecular-genetic processes remain largely unknown. We compared the gene expression profiles of abnormal stamens with that of normal stamens by RNA-Seq analysis, and identified a large number of differentially expressed genes between abnormal and normal stamens. In accordance with flower morphology, the expression of B-class MADS-box genes (ApAP3, ApTM6, and ApPI) was markedly reduced in pistillate stamens. However, most of the genes involved in meiosis were expressed normally in stamens with male-sterile anthers. In addition to verifying the expression patterns of genes previously known to be related to stamen and pollen grain development, we also identified previously unknown molecular phenotypes associated with sexual dysfunction in A. philoxeroides, that is helpful for dissecting the molecular mechanisms underpinning various male-sterile phenotypes and the molecular processes underlying the transition from sexuality to asexuality in clonal plants.
Project description:Alternanthera philoxeroides is an amphibious invasive weed that can colonize both aquatic and terrestrial habitats. Individuals growing in different habitats exhibit extensive phenotypic variation but little genetic differentiation. Little is known about the molecular basis underlying environment-induced phenotypic changes. Variation in transcript abundance in A. philoxeroides was characterized throughout the time-courses of pond and upland treatments using RNA-Sequencing. Seven thousand eight hundred and five genes demonstrated variable expression in response to different treatments, forming 11 transcriptionally coordinated gene groups. Functional enrichment analysis of plastically expressed genes revealed pathway changes in hormone-mediated signaling, osmotic adjustment, cell wall remodeling, and programmed cell death, providing a mechanistic understanding of the biological processes underlying the phenotypic changes in A. philoxeroides. Both transcriptional modulation of environmentally sensitive loci and environmentally dependent control of regulatory loci influenced the plastic responses to the environment. Phenotypic responses and gene expression patterns to contrasting hydrological conditions were compared between A. philoxeroides and its alien congener Alternanthera pungens. The terricolous A. pungens displayed limited phenotypic plasticity to different treatments. It was postulated based on gene expression comparison that the interspecific variation in plasticity between A. philoxeroides and A. pungens was not due to environmentally-mediated changes in hormone levels but to variations in the type and relative abundance of different signal transducers and receptors expressed in the target tissue.
Project description:Alternanthera philoxeroides (Mart.) Griseb. is an invasive herbaceous amphibious weed species in China. A pyralid moth Herpetogramma basalis (Walker) was discovered feeding on A. philoxeroides through field surveys and may be a potentially useful biocontrol agent. To determine the host range of H. basalis and evaluate its potential to control A. philoxeroides, no-choice and multiple-choice tests were conducted. Herpetogramma basalis fed on target weeds and 29 nontarget plant species. In addition to the target weed A. philoxeroides, H. basalis developed to adult on eight other nontarget species. Herpetogramma basalis survived to adulthood successfully on A. philoxeroides and less successfully on several other Amaranthaceae species. In multiple-choice studies, H. basalis showed a strong oviposition preference for A. philoxeroides over Amaranthus tricolor L. (Centrospermae: Amaranthaceae). Amaranthus tricolor was the only crop plant that supported the complete development of H. basalis. We cautiously recommend H. basalis for the biological control of A. philoxeroides in China.