Carlos R. Figueroa

Characterization of two divergent cDNAs encoding xyloglucan endotransglycosylase/hydrolase (XTH) expressed in Fragaria chiloensis fruit.

Chilean strawberry (Fragaria chiloensis), the maternal progenitor of Fragaria×ananassa, has emerged as a new berry fruit with excellent organoleptic characteristics. The fast softening of strawberries is a limiting step for their commercialization. Fruit softening has been shown to be related to cell wall degradation. Several enzymatic activities related to this process have been isolated in strawberry fruit, however xyloglucan endotransglycosylase/hydrolase (XTH) enzymes have not been identified or characterized so far. Two XTH genes were identified in an EST database of F. chiloensis fruit with high homology to other plant XTHs. We isolated the full-length cDNAs associated to these ESTs in F. chiloensis (Fc-XTH1, Fc-XTH2). Phylogenetic analysis suggests that both F. chiloensis XTH genes belong to distant phylogenetic groups of XTHs. Moreover, DNA gel-blot analysis indicates different genomic organization between the two genes. By means of Real Time qPCR analysis, gene expression profiles show a transcriptional profile of Fc-XTH1 transcripts congruent with a probable role during strawberry ripening, while that exhibited by Fc-XTH2 could be related with vegetative processes like leaf growth. On the other hand, immunodetection and enzyme activity assays allow the detection of XTH-related proteins and high xyloglucan transglycosylating (XETA) and degrading (XDA) activities at the turning stage. The data presented confirms the existence of two divergent XTH genes, and XET and XEH activities, in F. chiloensis fruit.

Transcript profiling suggests transcriptional repression of the flavonoid pathway in the white-fruited Chilean strawberry, Fragaria chiloensis (L.) Mill.

Beyond their participation in fruit pigmentation and because of their high antioxidant activity, flavonoids are considered important constituents of fruits and vegetables. We have previously reported that in the ripe receptacles of Fragaria chiloensis only traces of flavonoids can be found, while cinnamic acid derivatives are highly accumulated. In order to characterize the molecular background of this uncommon phenotype we analyzed the transcriptional profile of different biosynthetic genes, with special regard to the gene encoding Cinnamate 4-Hydroxylase (C4H), the enzyme transforming cinnamic acid into the next intermediary of the phenylpropanoid pathway. Northern blot and quantitative RT-PCR showed low transcript abundance for the gene encoding C4H and also for a series of structural genes responsible for flavonoid biosynthesis. Together with this, high transcript levels were found for a repressive transcription factor, suggesting that the pathway would be inhibited at the transcriptional level, thus correlating to our previous findings on the chemical phenotype. Our results contribute to the comprehension of the pigmentation phenotype in strawberries, allowing the utilization of Fragaria chiloensis as a model system for the study of antioxidant pigment biosynthesis.

Jasmonate Metabolism and Its Relationship with Abscisic Acid During Strawberry Fruit Development and Ripening

The plant hormone jasmonoyl-isoleucine (JA-Ile) is involved in stress response, development, and secondary metabolite production, although its role in fruit development and ripening remains unknown. The aim of this study is to describe variations of endogenous jasmonate (JAs) contents and JA metabolism-related genes in order to associate these to the evolution of abscisic acid (ABA) content during development and ripening of strawberry (Fragaria × ananassa Duch. cv. Aromas) fruit. A quantitative analysis of phytohormones and gene expression was carried out using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) and quantitative reverse transcription PCR (RT-qPCR) assays, respectively. The expression of genes encoding for JA metabolism enzymes exhibited a significant decrease concomitant to reduction of JAs and an increment of ABA levels from flowering to ripening stages. Exogenous application of methyl jasmonate (MeJA) triggered anthocyanin accumulation along with an increase in JA-Ile, JA, and MeJA levels, and a concomitant decrease in ABA. Together, these results provide insights into JAs homeostasis during strawberry fruit development, suggesting that MeJA-induced anthocyanin accumulation could be mediated by the activation of the JA signaling pathway. Furthermore, we propose an antagonistic relationship from the JA to the ABA pathway during non-climacteric strawberry fruit development and ripening.

Characterization of fruit development and potential health benefits of arrayan (Luma apiculata), a native berry of South America

The arrayan berry (Luma apiculata) is a native fruit from South America that belongs to the Myrtaceae family. To elucidate and characterize the developmental process and the potential health benefits of this edible fruit, quality and physiological parameters, along with antioxidant capacity, were evaluated during four clearly defined developmental stages of the fruit in two seasons. Fruit firmness slowly decreases during fruit development, whereas the solid soluble content/titratable acidity ratio (SSC/TA) increases significantly in the final stages of development. The measurement of low respiration rates and low ethylene production during growth and ripening suggested that the arrayan berry should be classified as a non-climacteric fruit. Arrayan berries show a significant increase in their antioxidant capacity from small green to black ripe fruit. FRAP and TEAC assays showed high correlations with total polyphenolic content (TPC) during ripening and high antioxidant capacity at all fruit stages, showing greater values in ripe fruit (FRAP: 24 ± 2 and 28 ± 3 μM FeSO4/gFW; TEAC: 18 ± 2 and 20 ± 1 Eq. Trolox/gFW for each season, respectively) than those observed in the blueberry (FRAP: 10 ± 2 and 19 ± 3 μM FeSO4/gFW; TEAC: 10 ± 2 and 17 ± 3). In addition, bioactive assays using ripe fruit extracts show presence of flavonol and anthocyanins, a high ORAC value (62,500 ± 7000 μmol/gDW) and a concentration-dependent vascular protection under high glucose conditions. The results obtained show that these endemic berry fruits have a promising potential as functional food.