A De novo Transcriptomic Approach to Identify Flavonoids and Anthocyanins “Switch-Off” in Olive (Olea europaea L.) Drupes at Different Stages of Maturation

Abstract

Highlights A de novo transcriptome reconstruction of olive drupes was performed in two genotypesGene expression was monitored during drupe development in two olive cultivarsTranscripts involved in flavonoid and anthocyanin pathways were analyzed in Cassanese and Leucocarpa cultivarsBoth cultivar and developmental stage impact gene expression in Olea europaea fruits.During ripening, the fruits of the olive tree (Olea europaea L.) undergo a progressive chromatic change characterized by the formation of a red-brown “spot” which gradually extends on the epidermis and in the innermost part of the mesocarp. This event finds an exception in the Leucocarpa cultivar, in which we observe a destabilized equilibrium between the metabolisms of chlorophyll and other pigments, particularly the anthocyanins whose switch-off during maturation promotes the white coloration of fruits. Despite its importance, genomic information on the olive tree is still lacking. Different RNA-seq libraries were generated from drupes of “Leucocarpa” and “Cassanese” olive genotypes, sampled at 100 and 130 days after flowering (DAF), and were used in order to identify transcripts involved in the main phenotypic changes of fruits during maturation and their corresponding expression patterns. A total of 103,359 transcripts were obtained and 3792 and 3064 were differentially expressed in “Leucocarpa” and “Cassanese” genotypes, respectively, during 100–130 DAF transition. Among them flavonoid and anthocyanin related transcripts such as phenylalanine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumarate-CoA ligase (4CL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonol 3′-hydrogenase (F3′H), flavonol 3′5 ′-hydrogenase (F3′5′H), flavonol synthase (FLS), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), UDP-glucose:anthocianidin: flavonoid glucosyltransferase (UFGT) were identified. These results contribute to reducing the current gap in information regarding metabolic processes, including those linked to fruit pigmentation in the olive.

Transcriptomic analysis of Lycium ruthenicum Murr. during fruit ripening provides insight into structural and regulatory genes in the anthocyanin biosynthetic pathway

“…During fruit formation and ripening in many plants, anthocyanin synthesis is enhanced by the co-regulation of a suite of TFs. Anthocyanins are considered as effective markers for monitoring ripening stages and the organoleptic quality of fruits [25]. Fang et al [8] demonstrated that the color of 'Furongli' plum (Prunus salicina) changed from green to red during ripening, which was associated with an evident increase in the anthocyanin content, being 53.85-fold higher at 135 days after flowering (DAF) in comparison to that at 105 DAF.…”

De Novo transcriptome characterization of Dracaena cambodiana and analysis of genes involved in flavonoid accumulation during formation of dragon’s blood

“…Specially, it has been widely applied to investigate molecular mechanisms of flavonoids accumulation in plant species such as Dioscorea alata 16, Prunus avium 17, Olea europaea 18 and Gentiana straminea 19. Here, we present the transcriptome analysis of D. cambodiana using RNA-Seq complemented with HPLC flavonoid profiling to identify potential candidate genes involved in flavonoids accumulation.…”

De NovoTranscriptome Sequencing ofOlea europaeaL. to Identify Genes Involved in the Development of the Pollen Tube

“…In order to obtain a general overview of the transcripts and metabolic pathways during pollen tube growth and to avoid cross contamination from nonhomogeneous tissue separation, sample pooling strategy was used here [ 11 , 12 ]. Pooling reduces variability by minimising individual variation and represents an alternative approach to biological replicates in experiments where interest does not focus on the individual but rather on characteristics of the population (e.g., common changes in expression patterns) [ 13 , 14 ].…”

“…Each sequence set was filtered with these criteria: first, the read containing the sequencing adaptor was removed; second, the reads with unknown nucleotides comprising more than 5% were removed; and third, low-quality reads with ambiguous sequence “N” were trimmed and discarded. Subsequently, without a reference genome a de novo assembly of the clean reads into transcripts was performed using Trinity, a novel method for the efficient and robust de novo reconstruction of transcriptomes from RNA-Seq data [ 11 , 16 – 23 ].…”