Transcripts switched off at the stop of phloem unloading highlight the energy efficiency of sugar import in the ripeningV. viniferafruit

Abstract

Transcriptomic changes at the cessation of sugar accumulation in the pericarp of Vitis vinifera were addressed on single berries re-synchronized according to their individual growth patterns. The net rates of water, sugars and K+ accumulation inferred from individual growth and solute concentration confirmed that these inflows stopped simultaneously in the ripe berry, while the small amount of malic acid remaining at this stage was still being oxidized at a low rate. Resynchronized individual berries displayed negligible variations in gene expression among triplicates. RNA-Seq studies revealed sharp reprogramming of cell wall enzymes and structural proteins, associated with an 80% repression of specific sugar transporters and aquaporins on the plasma or tonoplast membranes, at the stop of phloem unloading in the three genotypes and two environments investigated. The prevalence of SWEET transporters suggests that electrogenic transporters would just play a minor role on the plasma membrane of SE/CC complex, and the one of the flesh, while sucrose/H+ exchangers dominate on its tonoplast. Cis-regulatory elements present in their promoters allowed to sort these transporters in different groups, also including specific TIPs and PIPs paralogs, and cohorts of cell wall related genes. These results lead us to propose which structural, developmental and energy adaptations would give this fruit such a power of attraction for water and photoassimilates.

The sugarless grape trait characterized by single berry phenotyping

“…In most comparative studies, authors predetermine an average harvest date, ripening duration, thermal time or even [Hex] threshold to compare accessions at an hopefully similar ripe stage, in contradiction with the recognized impact of GxE on these variables (Liu et al, 2007; Dai et al, 2011; Duchêne et al, 2012). To circumvent this inconsistency and lack of consensus, the moment at which berry phloem unloading stops was recently proposed as a relevant definition of ripe stage both on the physiological and transcriptomic point of views (Bigard et al, 2018 and 2020; Shahood et al, 2015 and 2020; Savoi et al, 2021). This key transition which marks the arrest of the most intensive fruit biochemical pathways is associated with the transcriptional extinction of many genes encoding, amongst other, sugar transporters, aquaporins and cell wall-related enzymes (Savoi et al, 2021).…”

“…To circumvent this inconsistency and lack of consensus, the moment at which berry phloem unloading stops was recently proposed as a relevant definition of ripe stage both on the physiological and transcriptomic point of views (Bigard et al, 2018 and 2020; Shahood et al, 2015 and 2020; Savoi et al, 2021). This key transition which marks the arrest of the most intensive fruit biochemical pathways is associated with the transcriptional extinction of many genes encoding, amongst other, sugar transporters, aquaporins and cell wall-related enzymes (Savoi et al, 2021). Unfortunately, this developmental stage can’t be directly inferred from [Hex] kinetics, which continue to evolve after the completion of sugar storage (or accumulation) due to subsequent berry shriveling.…”

“…Thus, additional information on berry growth is required to address the net rates of sugar accumulation and malic acid breakdown in berries, together with their respective timings. Very recently, single berry phenotyping approaches improved our understanding of berry growth and metabolism during ripening, avoiding the biases due to berry asynchronicity (Shahood et al, 2020; Savoi et al, 2021). According to this new paradigm, this study aims to decipher the genetic differences existing for [Hex] and fruit acidity in a set of genotypes encompassing traditional varieties and new hybrids exhibiting low [Hex] at harvest (Escudier et al, 2017; Ojeda et al, 2017).…”

The Application of Ozonated Water Rearranges the Transcriptome of the Vitis Vinifera L. Fruit

“…Berry softening marks the onset of the massive import of sugars in grapevine. Surprisingly, VviSWEET10, which is implicated in the unloading of phloem sucrose inside the berry 23 , was up-regulated in BR together with two TIPs, aquaporins of the vacuole. But the expression of VviHT6, the major sucrose transporter on the tonoplast, was not affected, leaving open the question of a possible enhancement of the ripening program under ozonated water.…”

“…Carrying the Vvigai1 mutation, microvines exhibit a continuous owering, simultaneously displaying all the successive stages of fruit development on a single shoot 15 . This model has already facilitated transcriptomics approaches of the circadian cycle 16 , high-temperature stresses 17,18 , metabolomics works surveying glycosylated aroma precursors 19,20 , and several berry developmental studies [21][22][23] .…”