Clathrin Heavy Chain subunits coordinate endo- and exocytic traffic and affect stomatal movement

The current model for vesicular traffic to and from the plasma membrane is accepted but the molecular requirements for this coordination are not well defined. We have identified the has1 mutant, which has a stomatal function defect, as a clathrin heavy chain 1 (CHC1) mutant allele and show that it has a decreased rate of endocytosis and growth defects that are shared with other chc1 mutant alleles. We used chc1 alleles and the related chc2 mutant as tools to investigate the effects clathrin defects have on secretion pathways and plant growth. We show that secretion and endocytosis at the plasma membrane is sensitive to CHC1 and CHC2 function in seedling roots, and that chc mutants have physiological defects in stomatal function and plant growth that have not been previously described. These findings suggest that clathrin supports specific functions of multiple cell types. Stomata movement and gas exchange is altered in chc mutants, indicating clathrin is important for stomatal regulation. The aberrant function of chc mutant stomata is consistent with the growth phenotypes observed under different water and light conditions, which are also similar to those of the secretory SNARE mutant, syp121. The syp121 and chc mutants have impaired endo- and exocytosis compared to wild type, indicating a link between SYP121-dependent secretion and clathrin-dependent endocytosis at the plasma membrane. Our findings provide evidence that clathrin and SYP121 functions are important for the coordination of endo- and exocytosis, and have an impact on stomatal function, gas exchange, and vegetative growth in Arabidopsis

A mechanosensory receptor required for food texture detection in Drosophila.

Textural properties provide information on the ingestibility, digestibility and state of ripeness or decay of sources of nutrition. Compared with our understanding of the chemosensory assessment of food, little is known about the mechanisms of texture detection. Here we show that Drosophila melanogaster can discriminate food texture, avoiding substrates that are either too hard or too soft. Manipulations of food substrate properties and flies' chemosensory inputs indicate that texture preferences are revealed only in the presence of an appetitive stimulus, but are not because of changes in nutrient accessibility, suggesting that animals discriminate the substrates' mechanical characteristics. We show that texture preference requires NOMPC, a TRP-family mechanosensory channel. NOMPC localizes to the sensory dendrites of neurons housed within gustatory sensilla, and is essential for their mechanosensory-evoked responses. Our results identify a sensory pathway for texture detection and reveal the behavioural integration of chemical and physical qualities of food

Autofluorescence-Based Identification and Functional Validation of Antennal Gustatory Sensilla in a Specialist Leaf Beetle

Herbivorous insects mainly rely on their sense of taste to decode the chemical composition of potential hosts in close range. Beetles for example contact and scan leaves with their tarsi, mouthparts and antennal tips, i.e., appendages equipped with gustatory sensilla, among other sensillum types. Gustatory neurons residing in such uniporous sensilla detect mainly non-volatile compounds that contribute to the behavioral distinction between edible and toxic plants. However, the identification of gustatory sensilla is challenging, because an appendage often possesses many sensilla of distinct morphological and physiological types. Using the specialized poplar leaf beetle (Chrysomela populi, Chrysomelidae), here we show that cuticular autofluorescence scanning combined with electron microscopy facilitates the identification of antennal gustatory sensilla and their differentiation into two subtypes. The gustatory function of sensilla chaetica was confirmed by single sensillum tip-recordings using sucrose, salicin and salt. Sucrose and salicin were found at higher concentrations in methanolic leaf extracts of poplar (Populus nigra) as host plant compared to willow (Salix viminalis) as control, and were found to stimulate feeding in feeding choice assays. These compounds may thus contribute to the observed preference for poplar over willow leaves. Moreover, these gustatory cues benefited the beetle’s performance since weight gain was significantly higher when C. populi were reared on leaves of poplar compared to willow. Overall, our approach facilitates the identification of insect gustatory sensilla by taking advantage of their distinct fluorescent properties. This study also shows that a specialist beetle selects the plant species that provides optimal development, which is partly by sensing some of its characteristic non-volatile metabolites via antennal gustatory sensilla

Drosophila TRPA Channel Painless Inhibits Male–Male Courtship Behavior through Modulating Olfactory Sensation

The Drosophila melanogaster TRPA family member painless, expressed in a subset of multidendritic neurons embeding in the larval epidermis, is necessary for larval nociception of noxious heat or mechanical stimuli. However, the function of painless in adult flies remains largely unknown. Here we report that mutation of painless leads to a defect in male–male courtship behavior and alteration in olfaction sensitivity in adult flies. Specific downregulation of the expression of the Painless protein in the olfactory projection neurons (PNs) of the antennal lobes (ALs) resulted in a phenotype resembling that found in painless mutant flies, whereas overexpression of Painless in PNs of painless mutant males suppressed male–male courtship behavior. The downregulation of Painless exclusively during adulthood also resulted in male–male courtship behavior. In addition, mutation of the painless gene in flies caused changes in olfaction, suggesting a role for this gene in olfactory processing. These results indicate that functions of painless in the adult central nervous system of Drosophila include modulation of olfactory processing and inhibition of male–male courtship behavior

The DAG1 transcription factor negatively regulates the seed-to-seedling transition in Arabidopsis acting on ABA and GA levels

BACKGROUND: In seeds, the transition from dormancy to germination is regulated by abscisic acid (ABA) and gibberellins (GAs), and involves chromatin remodelling. Particularly, the repressive mark H3K27 trimethylation (H3K27me3) has been shown to target many master regulators of this transition. DAG1 (DOF AFFECTING GERMINATION1), is a negative regulator of seed germination in Arabidopsis, and directly represses the GA biosynthetic gene GA3ox1 (gibberellin 3-β-dioxygenase 1). We set to investigate the role of DAG1 in seed dormancy and maturation with respect to epigenetic and hormonal control. RESULTS: We show that DAG1 expression is controlled at the epigenetic level through the H3K27me3 mark during the seed-to-seedling transition, and that DAG1 directly represses also the ABA catabolic gene CYP707A2; consistently, the ABA level is lower while the GA level is higher in dag1 mutant seeds. Furthermore, both DAG1 expression and protein stability are controlled by GAs. CONCLUSIONS: Our results point to DAG1 as a key player in the control of the developmental switch between seed dormancy and germination

Male Moth Songs Tempt Females to Accept Mating: The Role of Acoustic and Pheromonal Communication in the Reproductive Behaviour of Aphomia sociella

Members of the subfamily Galleriinae have adapted to different selective environmental pressures by devising a unique mating process. Galleriinae males initiate mating by attracting females with either chemical or acoustic signals (or a combination of both modalities). Six compounds considered candidates for the sex pheromone have recently been identified in the wing gland extracts of Aphomia sociella males. Prior to the present study, acoustic communication had not been investigated. Signals mediating female attraction were likewise unknown.Observations of A. sociella mating behaviour and recordings of male acoustic signals confirmed that males initiate the mating process. During calling behaviour (stationary wing fanning and pheromone release), males disperse pheromone from their wing glands. When a female approaches, males cease calling and begin to produce ultrasonic songs as part of the courtship behaviour. Replaying of recorded courting songs to virgin females and a comparison of the mating efficiency of intact males with males lacking tegullae proved that male ultrasonic signals stimulate females to accept mating. Greenhouse experiments with isolated pheromone glands confirmed that the male sex pheromone mediates long-range female attraction.Female attraction in A. sociella is chemically mediated, but ultrasonic communication is also employed during courtship. Male ultrasonic songs stimulate female sexual display and significantly affect mating efficiency. Considerable inter-individual differences in song structure exist. These could play a role in female mate selection provided that the female's ear is able to discern them. The A. sociella mating strategy described above is unique within the subfamily Galleriinae

Gustatory function of sensilla chaetica on the labial palps and antennae of three tortricid moths (Lepidoptera: Tortricidae)

In adult Lepidoptera the labial palps are best known for their role in CO2 detection, but they can also bear sensilla chaetica which function is unknown. The number and distribution of sensilla chaetica in labial palps was studied using a bright field microscope. To determine if these sensilla have a gustatory function, we performed single sensillum electrophysiology recordings from palp and antennal sensilla of adult moths of Cydia pomonella (L.), Grapholita molesta (Busck) and Lobesia botrana (Denis and Shieffermüller). Each sensillum was stimulated with 3 doses of one of four test stimulus (sucrose, fructose, KCl and NaCl). Overall, responses (spikes/s−1) increased with dose, and were higher in the palps than in the antennae, and higher to sugars than to salts. With sugars the response increased with concentration in the palp but not in the antenna. With salts there was a drop in response at the intermediate concentration. The number and position of sensilla chaetica on labial palps was variable among individuals. Sensilla were located in the most exposed areas of the palp. Differences in sensilla distribution were detected between species. Such differences among species and between palps and antenna suggest that taste sensilla on the palps have an unforeseen role in adaptation.CA was supported by a Ph.D. fellowship BES-2017-081131 from the Ministerio de Economía, Industria y Competitividad (MINECO, Spain) joint financing by the European Social Fund. This study was supported by research grants AGL2016-77373-C2-2-R MINECO and PID2019-107030RB-C22 MICINN

An Odorant Receptor from the Southern House Mosquito Culex pipiens quinquefasciatus Sensitive to Oviposition Attractants

Insect odorant receptors (ORs) are heteromers comprised of highly variable odorant-binding subunits associated with one conserved co-receptor. They are potential molecular targets for the development of novel mosquito attractants and repellents. ORs have been identified in the malaria mosquito, Anopheles gambiae, and in the yellow fever mosquito, Aedes aegypti. However, they are still unknown in the Southern house mosquito, Culex quinquefasciatus, which transmits pathogens that cause human diseases throughout the world, including West Nile Virus in the United States.We have employed a combination of bioinformatics, molecular cloning and electrophysiology approaches to identify and characterize the response profile of an OR in Cx. quinquefasciatus. First, we have unveiled a large multigenic family of one-hundred-fifty-eight putative ORs in this species, including a subgroup of conserved ORs in three mosquito species. Using the Xenopus oocytes expression system, we have determined the response profile of CquiOR2, an antennae-specific OR, which shares high identity with putative orthologs in Anopheles gambiae (AgamOR2) and Aedes aegypti (AaegOR2).We show that CquiOR2 is highly sensitive to indole, an oviposition attractant for Cx. quinquefasciatus. The response profile of CquiOR2 expressed in Xenopus oocytes resembles that of an olfactory receptor neuron housed in the antennal short blunt-tipped sensilla (A2) of Cx. quinquefasciatus, which are natural detectors for oviposition attractants. This first Culex OR de-orphanized is, therefore, a potential molecular target for screening oviposition attractants

Function and central projections of gustatory receptor neurons on the antenna of the noctuid moth Spodoptera littoralis

Chemosensory information is crucial for most insects to feed and reproduce. Olfactory signals are mainly used at a distance, whereas gustatory stimuli play an important role when insects directly contact chemical substrates. In noctuid moths, although the antennae are the main olfactory organ, they also bear taste sensilla. These taste sensilla detect sugars and hence are involved in appetitive learning but could also play an important role in food evaluation by detecting salts and bitter substances. To investigate this, we measured the responses of individual taste sensilla on the antennae of Spodoptera littoralis to sugars and salts using tip recordings. We also traced the projections of their neuronal axons into the brain. In each sensillum, we found one or two neurons responding to sugars: one NaCl-responsive and one water-sensitive neuron. Responses of these neurons were dose-dependent and similar across different locations on the antenna. Responses were dependent on the sex for sucrose and on both sex and location for glucose and fructose. We did not observe a spatial map for the projections from specific regions of the antennae to the deutocerebrum or the tritocerebrum/suboesophageal ganglion complex. In accordance with physiological recordings, back-fills from individual sensilla revealed up to four axons, in most cases targeting different projection zones