Source-to-sink transport of sugar is one of the major determinants of plant growth and relies on the efficient and controlled distribution of sucrose (and some other sugars such as raffinose and polyols) across plant organs through the phloem. However, sugar transport through the phloem can be affected by many environmental factors that alter source/sink relationships. In this paper, we summarize current knowledge about the phloem transport mechanisms and review the effects of several abiotic (water and salt stress, mineral deficiency, CO₂, light, temperature, air, and soil pollutants) and biotic (mutualistic and pathogenic microbes, viruses, aphids, and parasitic plants) factors. Concerning abiotic constraints, alteration of the distribution of sugar among sinks is often reported, with some sinks as roots favored in case of mineral deficiency. Many of these constraints impair the transport function of the phloem but the exact mechanisms are far from being completely known. Phloem integrity can be disrupted (e.g., by callose deposition) and under certain conditions, phloem transport is affected, earlier than photosynthesis. Photosynthesis inhibition could result from the increase in sugar concentration due to phloem transport decrease. Biotic interactions (aphids, fungi, viruses…) also affect crop plant productivity. Recent breakthroughs have identified some of the sugar transporters involved in these interactions on the host and pathogen sides. The different data are discussed in relation to the phloem transport pathways. When possible, the link with current knowledge on the pathways at the molecular level will be highlighted.

The function of ASR (ABA [abscisic acid]-, stress-, and ripening-induced) proteins remains unknown. A grape ASR, VvMSA, was isolated by means of a yeast one-hybrid approach using as a target the proximal promoter of a grape putative monosaccharide transporter (VvHT1). This promoter contains two sugar boxes, and its activity is induced by sucrose and glucose. VvMSA and VvHT1 share similar patterns of expression during the ripening of grape. Both genes are inducible by sucrose in grape berry cell culture, and sugar induction of VvMSA is enhanced strongly by ABA. These data suggest that VvMSA is involved in a common transduction pathway of sugar and ABA signaling. Gel-shift assays demonstrate a specific binding of VvMSA to the 160-bp fragment of the VvHT1 promoter and more precisely to two sugar-responsive elements present in this target. The positive regulation of VvHT1 promoter activity by VvMSA also is shown in planta by coexpression experiments. The nuclear localization of the yellow fluorescent protein–VvMSA fusion protein and the functionality of the VvMSA nuclear localization signal are demonstrated. Thus, a biological function is ascribed to an ASR protein. VvMSA acts as part of a transcription-regulating complex involved in sugar and ABA signaling.

Plant growth and development has to be continuously adjusted to the available resources. Their optimization requires the integration of signals conveying the plant metabolic status, its hormonal balance, and its developmental stage. Many investigations have recently been conducted to provide insights into sugar signaling and its interplay with hormones and nitrogen in the fine-tuning of plant growth, development, and survival. The present review emphasizes the diversity of sugar signaling integrators, the main molecular and biochemical mechanisms related to the sugar-signaling dependent regulations, and to the regulatory hubs acting in the interplay of the sugar-hormone and sugar-nitrogen networks. It also contributes to compiling evidence likely to fill a few knowledge gaps, and raises new questions for the future.

Background: In higher plants, sugars are not only nutrients but also important signal molecules. They are distributed through the plant via sugar transporters, which are involved not only in sugar long-distance transport via the loading and the unloading of the conducting complex, but also in sugar allocation into source and sink cells. The availability of the recently released grapevine genome sequence offers the opportunity to identify sucrose and monosaccharide transporter gene families in a woody species and to compare them with those of the herbaceous Arabidopsis thaliana using a phylogenetic analysis. Results: In grapevine, one of the most economically important fruit crop in the world, it appeared that sucrose and monosaccharide transporter genes are present in 4 and 59 loci, respectively and that the monosaccharide transporter family can be divided into 7 subfamilies. Phylogenetic analysis of protein sequences has indicated that orthologs exist between Vitis and Arabidospis. A search for cis-regulatory elements in the promoter sequences of the most characterized transporter gene families (sucrose, hexoses and polyols transporters), has revealed that some of them might probably be regulated by sugars. To profile several genes simultaneously, we created a macroarray bearing cDNA fragments specific to 20 sugar transporter genes. This macroarray analysis has revealed that two hexose (VvHT1, VvHT3), one polyol (VvPMT5) and one sucrose (VvSUC27) transporter genes, are highly expressed in most vegetative organs. The expression of one hexose transporter (VvHT2) and two tonoplastic monosaccharide transporter (VvTMT1, VvTMT2) genes are regulated during berry development. Finally, three putative hexose transporter genes show a preferential organ specificity being highly expressed in seeds (VvHT3, VvHT5), in roots (VvHT2) or in mature leaves (VvHT5). Conclusions: This study provides an exhaustive survey of sugar transporter genes in Vitis vinifera and revealed that sugar transporter gene families in this woody plant are strongly comparable to those of herbaceous species. Dedicated macroarrays have provided a Vitis sugar transporter genes expression profiling, which will likely contribute to understand their physiological functions in plant and berry development. The present results might also have a significant impact on our knowledge on plant sugar transporters.

Different lengths of the promoter of grape (Vitis vinifera) VvHT1 (Hexose Transporter 1) gene, which encodes a putative hexose transporter expressed during the ripening of grape, have been transcriptionally fused to the β-glucuronidase reporter gene. In transgenic tobacco (Nicotiana tabacum) transformed with these constructs,VvHT1 promoters were clearly responsible for the sink organ preferential expression. The potential sugar effectors ofVvHT1 promoter were studied in tobacco cv Bright-Yellow 2 cells transformed with chimeric constructs. Glucose (56 mm), sucrose (Suc; 58 mm), and the non-transported Suc isomer palatinose doubled the β-glucuronidase activity conferred by the VvHT1 promoter, whereas fructose did not affect it. These effects were the strongest with the 2.4-kb promoter, which contains all putative sugar-responsive elements (activating and repressing), but they were also significant with the 0.3-kb promoter, which contains only activating sugar boxes. The induction of VvHT1 expression by both Suc and palatinose was confirmed in the homologous grape berry cell culture. The data provide the first example of a putative sugar transporter, which is induced by both glucose and Suc in higher plants. Although induction ofVvHT1 expression by Suc does not require transport, the presence of glucosyl moiety is necessary for Suc sensing. These results provide new insights into sugar sensing and signaling in plants.

Background: For centuries roses have been selected based on a number of traits. Little information exists on the genetic and molecular basis that contributes to these traits, mainly because information on expressed genes for this economically important ornamental plant is scarce.Results: Here, we used a combination of Illumina and 454 sequencing technologies to generate information onRosa sp.transcripts using RNA from various tissues and in response to biotic and abiotic stresses. A total of 80714 transcript clusters were identified and 76611 peptides have been predicted among which 20997 have been clustered into 13900 protein families. BLASTp hits in closely related Rosaceae species revealed that about half of the predicted peptides in the strawberry and peach genomes have orthologs inRosadataset. Digital expression was obtained using RNA samples from organs at different development stages and under different stress conditions. qPCR validated the digital expression data for a selection of 23 genes with high or low expression levels. Comparative gene expression analyses between the different tissues and organs allowed the identification of clusters that are highly enriched in given tissues or under particular conditions, demonstrating the usefulness of the digital gene expression analysis. A web interfaceROSAseqwas created that allows data interrogation by BLAST, subsequent analysis of DNA clusters and access to thorough transcript annotation including best BLAST matches onFragaria vesca, Prunus persicaandArabidopsis. The rose peptides dataset was used to create theROSAcycresource pathway database that allows access to the putative genes and enzymatic pathways.Conclusions: The study provides useful information onRosaexpressed genes, with thorough annotation and an overview of expression patterns for transcripts with good accuracy.