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This introduction to the special issue deploys a framework, inspired by realist synthesis and introduced in Section 1, that aims to untangle the contexts, mechanisms, and outcomes associated with investments that link poverty reduction and rural prosperity within a broad agri-food systems perspective. Section 2 considers changes in contexts: Where are agricultural research investments most likely to be an engine of poverty reduction? Over the past 25 years, there have been profound changes in the development context of most countries, necessitating an update on strategic insights for research investment priorities relevant for the economic, political, social, environmental, and structural realities of the early 21st Century. Section 2 briefly surveys changes in these structural aspects of poverty and development processes in low-income countries, with particular attention to new drivers (e.g., urbanization, climate change) that will be of increasing salience in the coming decades. In Section 3, we turn to mechanisms: What are the plausible impact pathways and what evidence exists to test their plausibility? Poor farmers in the developing world are often the stated focus of public sector agricultural research. However, farmers are not the only potential beneficiaries of agricultural research; rural landless laborers, stakeholders along food value chains, and the urban poor can also be major beneficiaries of such research. Thus, there are multiple, interacting pathways through which agricultural research can contribute to reductions in poverty and associated livelihood vulnerabilities. This paper introduces an ex ante set of 18 plausible impact pathways from agricultural research to rural prosperity outcomes, employing bibliometric methods to assess the evidence underpinning causal links. In Section 4, we revisit the concept of desired impacts: When we seek poverty reduction, what does that mean and what measures are needed to demonstrate impact? The papers in this special issue are intended to yield insights to inform improvements in agricultural research that seeks to reduce poverty. History indicates that equity of distribution of gains matters hugely, and thus the questions of “who wins?” and “who loses?” must be addressed. Moreover, our understanding(s) of “poverty” and the intended outcomes of development investments have become much richer over the past 25 years, incorporating more nuance regarding gender, community differences, and fundamental reconsideration of the meaning of poverty and prosperity that are not captured by simple head count income or even living standard measures.

Sensory systems with high discriminatory power use neurons that express only one of several alternative sensory receptor proteins. This exclusive receptor gene expression restricts the sensitivity spectrum of neurons and is coordinated with the choice of their synaptic targets (1-3). However, little is known about how it is maintained throughout the life of a neuron. Here we show that the green-light sensing receptor rhodopsin 6 (Rh6) acts to exclude an alternative blue-sensitive rhodopsin 5 (Rh5) from a subset of Drosophila R8 photoreceptor neurons (4). Loss of Rh6 leads to a gradual expansion of Rh5 expression into all R8 photoreceptors of the ageing adult retina. The Rh6 feedback signal results in repression of the rh5 promoter and can be mimicked by other Drosophila rhodopsins; it is partly dependent on activation of rhodopsin by light, and relies on [G.sub.αq] activity, but not on the subsequent steps of the phototransduction cascade (5). Our observations reveal a thus far unappreciated spectral plasticity of R8 photoreceptors, and identify rhodopsin feedback as an exclusion mechanism., In the Drosophila visual system, rhodopsins (Rh), G-protein-coupled receptors, detect light and initiate the phototransduction cascade leading to depolarization of photoreceptor neurons (5). Each ommatidium, the unit eye of the [...]

One of the ways a cell can rapidly and tightly regulate gene expression is to target specific mRNAs for rapid decay. A number of mRNA instability sequences that mediate rapid mRNA decay have been identified, particularly from multicellular eukaryotes, but pinpointing the cellular components that play critical roles in sequence-specific decay in vivo has been more difficult. In contrast, general pathways of mRNA degradation in yeast have been well established through the analysis of mutants affecting the general mRNA decay machinery. Strategies to isolate mutants in sequence-specific mRNA decay pathways, although extremely limited so far, have the potential to be just as powerful. In the study reported here, a selection in transgenic plants allowed the isolation of rare mutants of Arabidopsis thaliana that elevate the abundance of mRNAs that contain the plant mRNA instability sequence called DST (downstream element). This instability sequence is highly conserved in unstable small auxin up RNA (SAUR) transcripts. Genetic analysis of two dst mutants isolated via this selection showed that they are incompletely dominant and represent two independent loci. In addition to affecting DST-containing transgene mRNAs, mutations at both loci increased the abundance of the endogenous DST-containing SAUR-AC1 mRNA, but not controls lacking DST sequences. That these phenotypes are caused by deficiencies in DST-mediated mRNA decay was supported by mRNA stability measurements in transgenic plants. Isolation of the dst mutants provides a means to study sequence-specific mRNA degradation in vivo and establishes a method to isolate similar mutants from other organisms.