A trans-acting system has been designed in order to explore the three-dimensional structure of the anti-genomic HDV ribozyme. In this system, the substrate (SANT) is associated by base-pairing to the catalytic RNA (RzANT) forming helix H1. RzANT is able to cleave specifically the RNA substrate as well as a deoxysubstrate analogue containing a single ribocytidine at the cleavage site (position -1). This demonstrates that such deoxysubstrate analogues are valuable tools for structural studies of this ribozyme domain. They form however weak complexes with RzANT which is due in part to their ability to fold as stable hairpins unlike the RNA substrate. Using a set of full deoxy or of mixed deoxy-ribo substrate analogues site-specific substituted with the photoaffinity probe deoxy-4-thiouridine, ds4U, at a defined position, we were able to determine a number of long range contacts between the substrate and the ribozyme core. In particular, crosslinks between substrate position -1 and position -2 with residues C15, G19 and C67, thought to be involved in the ribozyme catalytic site, were detected. A three dimensional model of the antigenomic ribozyme system, derived from the structure proposed by Tanner et al. [Current Biol (1994) 4, 488-498] for the genomic system was constructed. Apart from residue deletion or insertion, only minor accommodations were needed to account for all photocrosslinks but one which is attributed to an alternative hybridization of the substrate with the ribozyme. This study therefore further supports the structure proposed by Tanner et al. for the pseudoknot model.

Review Cite this article: Perez TM et al. 2018 Botanic gardens are an untapped resource for studying the functional ecology of tropical plants. Phil. Trans. R. Soc. B 374: 20170390. http://dx.One contribution of 16 to a theme issue 'Biological collections for understanding biodiversity in the Anthropocene'.Functional traits are increasingly used to understand the ecology of plants and to predict their responses to global changes. Unfortunately, trait data are unavailable for the majority of plant species. The lack of trait data is especially prevalent for hard-to-measure traits and for tropical plant species, potentially owing to the many inherent difficulties of working with species in remote, hyperdiverse rainforest systems. The living collections of botanic gardens provide convenient access to large numbers of tropical plant species and can potentially be used to quickly augment trait databases and advance our understanding of species' responses to climate change. In this review, we quantitatively assess the availability of trait data for tropical versus temperate species, the diversity of species available for sampling in several exemplar tropical botanic gardens and the validity of garden-based leaf and root trait measurements. Our analyses support the contention that the living collections of botanic gardens are a valuable scientific resource that can contribute significantly to research on plant functional ecology and conservation.This article is part of the theme issue 'Biological collections for understanding biodiversity in the Anthropocene'.