No abstract

Animals utilize specialized sensory neurons enabling the detection of a wide range of environmental stimuli from the presence of toxic chemicals to that of touch. However, how these neurons discriminate between different kinds of stimuli remains poorly understood. By combining in vivo calcium imaging and molecular genetic manipulation, here we investigate the response patterns and the underlying mechanisms of the C. elegans phasmid neurons PHA/PHB to a variety of sensory stimuli. Our observations demonstrate that PHA/PHB neurons are polymodal sensory neurons which sense harmful chemicals, hyperosmotic solutions and mechanical stimulation. A repulsive concentration of IAA induces calcium elevations in PHA/PHB and both OSM-9 and TAX-4 are essential for IAA-sensing in PHA/PHB. Nevertheless, the PHA/PHB neurons are inhibited by copper and post-synaptically activated by copper removal. Neuropeptide is likely involved in copper removal-induced calcium elevations in PHA/PHB. Furthermore, mechanical stimulation activates PHA/PHB in an OSM-9-dependent manner. Our work demonstrates how PHA/PHB neurons respond to multiple environmental stimuli and lays a foundation for the further understanding of the mechanisms of polymodal signaling, such as nociception, in more complex organisms.

How neurons are capable of decoding stimulus intensity and translate this information into complex behavioral outputs is poorly defined. Here, we demonstrate that the C. elegans interneuron AIB regulates two types of behaviors: reversal initiation and feeding suppression in response to different concentrations of quinine. Low concentrations of quinine are decoded in AIB by a low-threshold, fast-inactivation glutamate receptor GLR-1 and translated into reversal initiation. In contrast, high concentrations of quinine are decoded by a high-threshold, slow-inactivation glutamate receptor GLR-5 in AIB. After activation, GLR-5 evokes sustained Ca2+ release from the inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ stores and triggers neuropeptide secretion, which in turn activates the downstream neuron RIM and inhibits feeding. Our results reveal that distinct signal patterns in a single interneuron AIB can encode differential behavioral outputs depending on the stimulus intensity, thus highlighting the importance of functional mapping of information propagation at the single-neuron level during connectome construction.

Bamboo, a non-timber grass species, known for exceptionally fast growth is a commercially viable crop. Long terminal repeat (LTR) retrotransposons, the main class I mobile genetic elements in plant genomes, are highly abundant (46%) in bamboo, contributing to genome diversity. They play significant roles in the regulation of gene expression, chromosome size and structure as well as in genome integrity. Due to their random insertion behavior, interspaces of retrotransposons can vary significantly among bamboo genotypes. Capitalizing this feature, inter-retrotransposon amplified polymorphism (IRAP) is a high-throughput marker system to study the genetic diversity of plant species. To date, there are no transposon based markers reported from the bamboo genome and particularly using IRAP markers on genetic diversity. Phyllostachys genus of Asian bamboo is the largest of the Bambusoideae subfamily, with great economic importance. We report structure-based analysis of bamboo genome for the LTR-retrotransposon superfamilies, Ty3-gypsy and Ty1-copia, which revealed a total of 98,850 retrotransposons with intact LTR sequences at both the ends. Grouped into 64,281 clusters/scaffold using CD-HIT-EST software, only 13 clusters of retroelements were found with more than 30 LTR sequences and with at least one copy having all intact protein domains such as gag and polyprotein. A total of 16 IRAP primers were synthesized, based on the high copy numbers of conserved LTR sequences. A study using these IRAP markers on genetic diversity and population structure of 58 Asian bamboo accessions belonging to the genus Phyllostachys revealed 3340 amplicons with an average of 98% polymorphism. The bamboo accessions were collected from nine different provinces of China, as well as from Italy and America. A three phased approach using hierarchical clustering, principal components and a model based population structure divided the bamboo accessions into four sub-populations, PhSP1, PhSP2, PhSP3 and PhSP4. All the three analyses produced significant sub-population wise consensus. Further, all the sub-populations revealed admixture of alleles. The analysis of molecular variance (AMOVA) among the sub-populations revealed high intra-population genetic variation (75%) than inter-population. The results suggest that Phyllostachys bamboos are not well evolutionarily diversified, although geographic speciation could have occurred at a limited level. This study highlights the usability of IRAP markers in determining the inter-species variability of Asian bamboos.