Evidence shows the importance of food systems for sustainable development: they are at the nexus that links food security, nutrition, and human health, the viability of ecosystems, climate change, and social justice. However, agricultural policies tend to focus on food supply, and sometimes, on mechanisms to address negative externalities. We propose an alternative. Our starting point is that agriculture and food systems’ policies should be aligned to the 2030 Agenda for Sustainable Development. This calls for deep changes in comparison with the paradigms that prevailed when steering the agricultural change in the XXth century. We identify the comprehensive food systems transformation that is needed. It has four parts: first, food systems should enable all people to benefit from nutritious and healthy food. Second, they should reflect sustainable agricultural production and food value chains. Third, they should mitigate climate change and build resilience. Fourth, they should encourage a renaissance of rural territories. The implementation of the transformation relies on (i) suitable metrics to aid decision-making, (ii) synergy of policies through convergence of local and global priorities, and (iii) enhancement of development approaches that focus on territories. We build on the work of the “Milano Group,” an informal group of experts convened by the UN Secretary General in Milan in 2015. Backed by a literature review, what emerges is a strategic narrative linking climate, agriculture and food, and calling for a deep transformation of food systems at scale. This is critical for achieving the Sustainable Development Goals and the Paris Agreement. The narrative highlights the needed consistency between global actions for sustainable development and numerous local-level innovations. It emphasizes the challenge of designing differentiated paths for food systems transformation responding to local and national expectations. Scientific and operational challenges are associated with the alignment and arbitration of local action within the context of global priorities.

Summary• Here, we examine the influence of source-to-sink carbohydrate (CHO) flow on the development of constitutive and inducible levels of phenylpropenoids in hybrid poplar ( Populus nigra × P. deltoides ) foliage to determine if secondary metabolic processes in plant modules can be inhibited in a predictable manner by events such as herbivory and the development of new leaves and reproductive structures, which alter the path of phloem-borne resources.• Phenylpropenoid concentrations were determined for developing foliage after CHO flow, measured as the translocation of 13 C from labeled sources was manipulated.• Phenylpropenoid metabolism in both unwounded and induced sink leaves was directly and positively linked to rates of CHO import. Alterations in rates of translocation yielded different results, depending on how CHO import was affected: the removal of competing sinks rapidly and dramatically increased leaf phenolic contents, whereas phenolic levels (and their inducibility) tended to be reduced when import was interrupted.• High and inducible sink strength in developing poplar leaves provides resources for phenolic biosynthesis and, as a result, restrictions or re-directions of CHOs affect the foliar quality. Sink strength and the vascular architecture of plants, which confer upon them a modular nature, can determine the direction and magnitude of defense responses in trees.

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Marine protists of the genus Labyrinthula cause the seagrass wasting disease, which is associated with regional die-offs of eelgrass Zostera marina and also infects turtlegrass Thalassia testudinum. The ability of seagrasses to resist pathogen attack is determined by multiple factors, which are poorly understood. One factor hypothesized to influence seagrass disease resistance is the presence of (poly)phenolic natural products such as caffeic acid, which inhibits the growth of L. zosterae in in vitro laboratory bioassays. This hypothesis has been supported by reports of pathogen-induced phenolic accumulations in eelgrass Z. marina. To test the response of T. testudinum to inoculation with Labyrinthula sp., we conducted a series of culture experiments wherein plants were inoculated with Labyrinthula sp. isolated from turtlegrass beds in Perdido Bay, Florida (USA). Concentrations of phenolic acids and condensed tannins were quantified in diseased leaves as well as those treated with 5 mM salicylic acid, a signaling molecule associated with pathogen-induced responses in plants.In infection experiments, increases in the concentrations of several phenolic acids, but not condensed tannins, were observed in tissues above, but not below, microbial lesions. Salicylic acid (SA) treatments did not induce any phenolic compound, either when applied alone or in concert with the pathogen. The induction of phenolic acids above, but not below, infection sites suggests that T. testudinum leaves did not respond to the pathogen specifically. Instead, the pattern is consistent with the predictions of the sink/source model of plant defense, which predicts increased phenolic contents in cases where wounds disrupt plant resource allocation and cause a local overabundance of carbonbased resources. Thus, we suggest that the emergence of Labyrinthula sp. lesions on turtlegrass blades causes a 'pseudo-induction' of specific phenolics as carbon resources over-accumulate in tissues located above wound sites.

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