@article {113539, title = {An inducible potato (E,E)-farnesol synthase confers tolerance against bacterial pathogens in potato and tobacco.}, journal = {Plant J}, year = {2022}, month = {2022 Jul 02}, abstract = {

Terpene synthases (TPSs) have diverse biological functions in plants. Though the roles of TPSs in herbivore defense are well established in many plant species, their role in bacterial defense has been scarce and is emerging. Through functional genomics, here we report the in planta role of potato (Solanum tuberosum) terpene synthase (StTPS18) in bacterial defense. Expression of StTPS18 was highest in leaves and was induced in response to Pseudomonas syringae and methyl jasmonate treatments. The recombinant StTPS18 exhibited bona fide (E,E)-farnesol synthase activity forming a sesquiterpenoid, (E,E)-farnesol as the sole product, utilising (E,E)-farnesyl diphosphate (FPP). Subcellular localization of GFP fusion protein revealed that StTPS18 is localized to the cytosol. Silencing and overexpression of StTPS18 in potato resulted in reduced and enhanced tolerance, respectively, to bacterial pathogens P. syringae and Ralstonia solanacearum. Bacterial growth assay using medium containing (E,E)-farnesol significantly inhibited P. syringae growth. Moreover, StTPS18 overexpressing transgenic potato and Nicotiana tabacum leaves, and (E,E)-farnesol and P. syringae infiltrated potato leaves exhibited elevated expression of sterol pathway and members of pathogenesis-related genes with enhanced phytosterol accumulation. Interestingly, enhanced phytosterols in C -(E,E)-farnesol infiltrated potato leaves were devoid of any noticeable C labeling, indicating no direct utilization of (E,E)-farnesol in phytosterols formation. Furthermore, leaves of StTPS18 overexpressing transgenic lines had no detectable (E,E)-farnesol similar to the control plant, and emitted lower levels of sesquiterpenes than the control. These findings point towards an indirect involvement of StTPS18 and its product (E,E)-farnesol in bacterial defense through upregulation of phytosterol biosynthesis and defense genes.

}, issn = {1365-313X}, doi = {10.1111/tpj.15890}, author = {Dwivedi, Varun and Kumar, Sarma Rajeev and Shilpashree, H B and Krishna, Ram and Rao, Srinivas and Shasany, Ajit K and Olsson, Shannon B and Nagegowda, Dinesh A} } @article {83639, title = {Inhibition of plant pathogenic fungi by endophytic Trichoderma spp. through mycoparasitism and volatile organic compounds.}, journal = {Microbiol Res}, volume = {242}, year = {2021}, month = {2020 Sep 17}, pages = {126595}, abstract = {

Antagonism of plant pathogenic fungi by endophytic fungi is a well-known phenomenon. In plate assays, the antagonism could be due to mycoparasitism, competition for space or antibiosis, involving a chemical diffusate, or a volatile organic compound (VOC). In this study, we demonstrate that besides mycoparasitism, VOCs play a major role in antagonism of pathogenic fungi by four endophytic fungi belonging to the genus Trichoderma. Using a double-plate assay, we show that all the four endophytic Trichoderma species significantly inhibited mycelial growth of three of the four pathogens, (Sclerotinia sclerotiorum-TSS, Sclerotium rolfsii-CSR and Fusarium oxysporum-CFO), while that of Macrophomina phaseolina-CMP was not affected. GC-MS analysis of the pure cultures of one of the endophytic fungi studied, namely, Trichoderma longibrachiatum strain 2 (Acc. No. MK751758) and the pathogens, F. oxysporum-CFO and M. phaseolina-CMP revealed the presence of several VOCs including hydrocarbons, alcohols, ketones, aldehydes, esters, acids, ethers and different classes of terpenes. In mixed double plates, where the endophyte was grown along with either of the two plant pathogens, F. oxysporum-CFO or M. phaseolina-CMP, there was an induction of a number of new VOCs that were not detected in the pure cultures of either the endophyte or the pathogens. Several of these new VOCs are reported to possess antifungal and cytotoxic activity. We discuss these results and highlight the importance of such interactions in endophyte-pathogen interactions.

}, issn = {1618-0623}, doi = {10.1016/j.micres.2020.126595}, author = {Rajani, P and Rajasekaran, C and Vasanthakumari, M M and Olsson, Shannon B and Ravikanth, G and Uma Shaanker, R} } @article {12202, title = {Identification of Host Fruit Volatiles from Snowberry (Symphoricarpos albus), Attractive to Rhagoletis zephyria Flies from the Western United States.}, journal = {J Chem Ecol}, year = {2017}, month = {2017 Jan 11}, abstract = {

A mixture of behaviorally active volatiles was identified from the fruit of snowberry, Symphoricarpos albus laevigatus, for Rhagoletis zephyria flies reared from snowberry fruit. A nine-component blend containing 3-methylbutan-1-ol (3\%), dimethyl trisulfide (1\%), 1-octen-3-ol (40\%), myrcene (8\%), nonanal (9\%), linalool (13\%), (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT, 6\%), decanal (15\%), and β-caryophyllene (5\%) was identified that gave consistent electroantennogram activity and was behaviorally active in flight tunnel tests. In other flight tunnel assays, snowberry flies from two sites in Washington state, USA, displayed significantly greater levels of upwind oriented flight to sources with the snowberry volatile blend compared with previously identified volatile blends from domestic apple (Malus domestica) and downy hawthorn (Crataegus mollis) fruit from the eastern USA, and domestic apple, black hawthorn (C. douglasii) and ornamental hawthorn (C. monogyna) from Washington state. Selected subtraction assays showed that whereas removal of DMNT or 1-octen-3-ol significantly reduced the level of upwind flight, removal of myrcene and β-caryophyllene, or dimethyl trisulfide alone did not significantly affect the proportion of upwind flights. Our findings add to previous studies showing that populations of Rhagoletis flies infesting different host fruit are attracted to unique mixtures of volatile compounds specific to their respective host plants. Taken together, the results support the hypothesis that differences among flies in their behavioral responses to host fruit odors represent key adaptations involved in sympatric host plant shifts, contributing to host specific mating and generating prezygotic reproductive isolation among members of the R. pomonella sibling species complex.

}, issn = {1573-1561}, doi = {10.1007/s10886-016-0814-8}, author = {Cha, Dong H and Olsson, Shannon B and Yee, Wee L and Goughnour, Robert B and Hood, Glen R and Mattsson, Monte and Schwarz, Dietmar and Feder, Jeffrey L and Linn, Charles E} } @article {26570, title = {In situ modeling of multimodal floral cues attracting wild pollinators across environments.}, journal = {Proc Natl Acad Sci U S A}, year = {2017}, month = {2017 Nov 27}, abstract = {

With more than 80\% of flowering plant species specialized for animal pollination, understanding how wild pollinators utilize resources across environments can encourage efficient planting and maintenance strategies to maximize pollination and establish resilience in the face of environmental change. A fundamental question is how generalist pollinators recognize "flower objects" in vastly different ecologies and environments. On one hand, pollinators could employ a specific set of floral cues regardless of environment. Alternatively, wild pollinators could recognize an exclusive signature of cues unique to each environment or flower species. Hoverflies, which are found across the globe, are one of the most ecologically important alternative pollinators after bees and bumblebees. Here, we have exploited their cosmopolitan status to understand how wild pollinator preferences change across different continents. Without employing any a priori assumptions concerning the floral cues, we measured, predicted, and finally artificially recreated multimodal cues from individual flowers visited by hoverflies in three different environments (hemiboreal, alpine, and tropical) using a field-based methodology. We found that although "flower signatures" were unique for each environment, some multimodal lures were ubiquitously attractive, despite not carrying any reward, or resembling real flowers. While it was unexpected that cue combinations found in real flowers were not necessary, the robustness of our lures across insect species and ecologies could reflect a general strategy of resource identification for generalist pollinators. Our results provide insights into how cosmopolitan pollinators such as hoverflies identify flowers and offer specific ecologically based cues and strategies for attracting pollinators across diverse environments.

}, issn = {1091-6490}, doi = {10.1073/pnas.1714414114}, author = {Nordstr{\"o}m, Karin and Dahlbom, Josefin and Pragadheesh, V S and Ghosh, Suhrid and Olsson, Amadeus and Dyakova, Olga and Suresh, Shravanti Krishna and Olsson, Shannon B} } @article {11619, title = {Intracellular regulation of the insect chemoreceptor complex impacts odour localization in flying insects.}, journal = {J Exp Biol}, volume = {219}, year = {2016}, month = {2016 Nov 01}, pages = {3428-3438}, abstract = {

Flying insects are well known for airborne odour tracking and have evolved diverse chemoreceptors. While ionotropic receptors (IRs) are found across protostomes, insect odorant receptors (ORs) have only been identified in winged insects. We therefore hypothesized that the unique signal transduction of ORs offers an advantage for odour localization in flight. Using Drosophila, we found expression and increased activity of the intracellular signalling protein PKC in antennal sensilla following odour stimulation. Odour stimulation also enhanced phosphorylation of the OR co-receptor Orco in vitro, while site-directed mutation of Orco or mutations in PKC subtypes reduced the sensitivity and dynamic range of OR-expressing neurons in vivo, but not IR-expressing neurons. We ultimately show that these mutations reduce competence for odour localization of flies in flight. We conclude that intracellular regulation of OR sensitivity is necessary for efficient odour localization, which suggests a mechanistic advantage for the evolution of the OR complex in flying insects.

}, issn = {1477-9145}, doi = {10.1242/jeb.143396}, author = {Getahun, Merid N and Thoma, Michael and Lavista-Llanos, Sofia and Keesey, Ian and Fandino, Richard A and Knaden, Markus and Wicher, Dieter and Olsson, Shannon B and Hansson, Bill S} }