In grapevine, anthocyanins and proanthocyanidins are the main flavonoids in berries, which are associated to organoleptic properties in red wine such as color and astringency. Flavonoid pathway is specifically regulated at transcriptional level and several R2R3-MYB proteins have shown to act as positive regulators. However, some members of this family have shown to repress the flavonoid biosynthesis. In this work, we present the characterization of VvMYB4-like gene, which encodes a putative transcriptional factor highly expressed in the skin of berries at the pre veraison stage in grapevine. Its over-expression in tobacco resulted in the loss of pigmentation in flowers due a decrease in anthocyanin accumulation. Severity in anthocyanin suppression observed in petals could be associated with the expression level of the VvMYB4-like transgene. Expression analysis of flavonoid structural genes revealed the strong down-regulation of the flavonoid-related genes anthocyanidin synthase (ANS) and dihydroflavonol reductase (DFR) genes and also the reduction of the anthocyanin-related gene UDP glucose:flavonoid 3-O-glucosyl transferase (UFGT), which was dependent of the transgene expression. In addition, expression of VvMYB4-like in the model plant Arabidopsis showed similar results, with the higher down-regulation observed in the AtDFR and AtLDOX genes. These results suggest that VvMYB4-like may play an important role in regulation of anthocyanin biosynthesis in grapevine acting as a transcriptional repressor of flavonoid structural genes.

VvMATE1 and VvMATE2 encode putative PA transporters expressed during seed development in grapevine. The subcellular localization of these MATE proteins suggests different routes for the intracellular transport of PAs. Proanthocyanidins (PAs), also called condensed tannins, protect plants against herbivores and are important quality components of many fruits. PAs biosynthesis is part of the flavonoid pathway that also produces anthocyanins and flavonols. In grape fruits, PAs are present in seeds and skin tissues. PAs are synthesized in the cytoplasm and accumulated into the vacuole and apoplast; however, little is known about the mechanisms involved in the transport of these compounds to such cellular compartments. A gene encoding a Multidrug And Toxic compound Extrusion (MATE) family protein suggested to transport anthocyanins-named VvMATE1-was used to identify a second gene of the MATE family, VvMATE2. Analysis of their deduced amino acid sequences and the phylogenetic relationship with other MATE-like proteins indicated that VvMATE1 and VvMATE2 encode putative PA transporters. Subcellular localization assays in Arabidopsis protoplasts transformed with VvMATE-GFP fusion constructs along with organelle-specific markers revealed that VvMATE1 is localized in the tonoplast whereas VvMATE2 is localized in the Golgi complex. Major expression of both genes occurs during the early stages of seed development concomitant with the accumulation of PAs. Both genes are poorly expressed in the skin of berries while VvMATE2 is also expressed in leaves. The presence of putative cis-acting elements in the promoters of VvMATE1 and VvMATE2 may explain the differential transcriptional regulation of these genes in grapevine. Altogether, these results suggest that these MATE proteins could mediate the transport and accumulation of PAs in grapevine through different routes and cellular compartments.

In Chile Vasconcellea pubescens is cropped to produce canned fruit, juice, jam and processed sweets. Additionally this species produces latex with a high level of papain, an important and valuable proteolytic enzyme with industrial applications. In this investigation seven ISSR primers were used to study the level and organization of genetic diversity in 333 samples of V. pubescens. Out of the 114 bands recorded, 63 proved to be polymorphic (P = 55.3%). At the species level, the genetic diversity was rather low (h = 0.01 ± 6,80188E-05, Shannon's Index I = 0.16 ± 0,000148). The major portion of the genetic diversity was found within groups (65%). The genetic differentiation between the different groups was significant, as the AMOVA analysis suggested (U pt = 0.35). When analysing the Northern area alone, the differentiation increased to U pt = 0.40. When only the Southern area was analysed, U pt decreased to 0.18, indicating greater genetic similarity among the samples. The results generated from Structure and Bayesian Analysis of Population Structure distinguished 8 genetically different groups, five of them located in the north and three in the south. The results are discussed in the light of the growers' practices.

Hexokinases (HXKs) and fructokinases (FRKs) are the only two families of enzymes in plants that have been identified as able to phosphorylate Glucose (Glc) and Fructose (Fru). Glc can only be phosphorylated in plants by HXKs, while Fru can be phosphorylated by either HXKs or FRKs. The various subcellular localizations of HXKs in plants indicate that they are involved in diverse functions, including anther dehiscence and pollen germination, stomatal closure in response to sugar levels, stomatal aperture and reducing transpiration. Its association with modulating programmed cell death, and responses to oxidative stress and pathogen infection (abiotic and biotic stresses) also have been reported. To extend our understanding about the function of HXK-like genes in the response of Prunus rootstocks to abiotic stress, we performed a detailed bioinformatic and functional analysis of hexokinase 3-like genes (HXK3s) from two Prunus rootstock genotypes, ‘M.2624’ (Prunus cerasifera Ehrh × P. munsoniana W.Wight & Hedrick) and ‘M.F12/1’ (P. avium L.), which are tolerant and sensitive to hypoxia stress, respectively. A previous large-scale transcriptome sequencing of roots of these rootstocks, showed that this HXK3-like gene that was highly induced in the tolerant genotype under hypoxia conditions. In silico analysis of gene promoters from M.2624 and M.F12/1 genotypes revealed regulatory elements that could explain differential transcriptional profiles of HXK3 genes. Subcellular localization was determinates by both bioinformatic prediction and expression of their protein fused to the green fluorescent protein (GFP) in protoplasts and transgenic plants of Arabidopsis. Both approaches showed that they are expressed in plastids. Metabolomics analysis of Arabidopsis plants ectopically expressing Prunus HXK3 genes revealed that content of several metabolites including phosphorylated sugars (G6P), starch and some metabolites associated with the TCA cycle were affected. These transgenic Arabidopsis plants showed improved tolerance to salt and drought stress under growth chamber conditions. Our results suggest that Prunus HXK3 is a potential candidate for enhancing tolerance to salt and drought stresses in stone fruit trees and other plants.

Rice ASR genes respond distinctly to abscisic acid, dehydration and cold stress. Their tissue-specific expression provides new hints about their possible roles in plant responses to stress. Plant ASR proteins have emerged as an interesting distinct group of proteins with apparent roles in protecting cellular structures as well as putative regulators of gene expression, both important responses of plants to environmental stresses. Regardless of the possible functions proposed by different studies, little is known about their role in cereals. To further understand the function of these proteins in the Gramineae, we investigated the expression pattern of the six ASR genes present in the rice genome in response to ABA, stress conditions and in different organs. Although transcription of most OsASRs is transiently enhanced by ABA treatment, the genes present a differential response under cold and drought stress as well as specific expression in certain tissues and organs. Analysis of their promoters reveals regulatory cis-elements associated to hormonal, sugar and stress responses. The promoters of two genes, OsASR1 and OsASR5, direct the expression of the GUS reporter gene especially to leaf vascular tissue in response to dehydration and low temperature. In control conditions, a GUS reporter assay also indicates specific expression of these two genes in roots, anthers and seed scutellar tissues. These results provide new clues about the possible role of ASRs in plant stress responses and development.