The secondary growth of a woody stem requires the formation of a vascular cambium at an appropriate position and proper patterning of the vascular tissues derived from the cambium. Class III homeodomain-leucine zipper (HD ZIP) transcription factors have been implicated in polarity determination and patterning in lateral organs and primary vascular tissues and in the initiation and function of shoot apical meristems. We report here the functional characterization of a Populus class III HD ZIP gene, popREVOLUTA (PRE), that demonstrates another role for class III HD ZIPs in regulating the development of cambia and secondary vascular tissues. PRE is orthologous to Arabidopsis (Arabidopsis thaliana) REVOLUTA and is expressed in both the shoot apical meristem and in the cambial zone and secondary vascular tissues. Transgenic Populus expressing a microRNAresistant form of PRE presents unstable phenotypic abnormalities affecting both primary and secondary growth. Surprisingly, phenotypic changes include abnormal formation of cambia within cortical parenchyma that can produce secondary vascular tissues in reverse polarity. Genes misexpressed in PRE mutants include transcription factors and auxin-related genes previously implicated in class III HD ZIP functions during primary growth. Together, these results suggest that PRE plays a fundamental role in the initiation of the cambium and in regulating the patterning of secondary vascular tissues.

The developmental mechanisms regulating cell differentiation and patterning during the secondary growth of woody tissues are poorly understood. Class III HD ZIP transcription factors are evolutionarily ancient and play fundamental roles in various aspects of plant development. Here we investigate the role of a Class III HD ZIP transcription factor, POPCORONA, during secondary growth of woody stems. Transgenic Populus (poplar) trees expressing either a miRNA-resistant POPCORONA or a synthetic miRNA targeting POPCORONA were used to infer function of POPCORONA during secondary growth. Whole plant, histological, and gene expression changes were compared for transgenic and wild-type control plants. Synthetic miRNA knock down of POPCORONA results in abnormal lignification in cells of the pith, while overexpression of a miRNA-resistant POPCORONA results in delayed lignification of xylem and phloem fibers during secondary growth. POPCORONA misexpression also results in coordinated changes in expression of genes within a previously described transcriptional network regulating cell differentiation and cell wall biosynthesis, and hormone-related genes associated with fiber differentiation. POPCORONA illustrates another function of Class III HD ZIPs: regulating cell differentiation during secondary growth.

No abstract

Global challenges such as climate change, increasing urbanization and a lack of transparency of food chains, have led to the development of innovative urban food production approaches, such as rooftop greenhouses, vertical farms, indoor farms, aquaponics as well as production sites for edible insects or micro-algae. Those approaches are still at an early stage of development and partly unknown among the public. The aim of our study was to identify the perception of sustainability, social acceptability and ethical aspects of these new approaches and products in urban food production. We conducted 19 qualitative expert interviews and applied qualitative content analysis. Our results revealed that major perceived benefits are educational effects, revaluation of city districts, efficient resource use, exploitation of new protein sources or strengthening of local economies. Major perceived conflicts concern negative side-effects, legal constraints or high investment costs. The extracted acceptance factors deal significantly with the "unknown". A lack of understanding of the new approaches, uncertainty about their benefits, concerns about health risks, a lack of familiarity with the food products, and ethical doubts about animal welfare represent possible barriers. We conclude that adaptation of the unsuitable regulatory framework, which discourages investors, is an important first step to foster dissemination of the urban food production approaches.