Elucidating the causes of firmness in blueberries (V. corymbosum): cell wall composition, ions and enzymes

MONTECCHIARINI, M.L.; GOLLÁN, A.; VAZQUEZ, D.E.; MORALES, L.; SILVA, C.; RIVADENEIRA, M.F.; BLANCO-HERRERA, F.; TRIPODI, K.E.J.; VALDERRAMO, L.; BELLO, F.; MARGARIT, E.

Mendoza

Congreso; SAIB-SAMIGE 2020-LVI Reunion Anual SAIB; 2020

SAIB

Blueberries (Vaccinium corymbosum) have been cultivated in Argentina since the mid 1990 decade and constitute a very profitable resource. Most of the production is exported to the northern hemisphere from September to December, when there is no local availability. Because ripening is non-homogeneous in the plant, considerable volumes of fruit must be stored under controlled conditions before being shipped. At the same time, transport is mainly by ship in order to reduce costs, which requires a long time of transport to the final destination. These factors make firmness a very relevant attribute in the blueberry since a soft fruit is frequently rejected by consumers, giving rise to economic loss. The pursuit of firmer and better-quality blueberries is a continuous task that aims at a more profitable production. To this end it is essential to understand the biological processes linked to fruit firmness, which may diverge among fruit tissues. By contrasting varieties with opposing firmness, we were able to elucidate the events that, taking place at immature stages, lay the foundation to produce a firmer ripe fruit. A deep study of blueberry skin was carried out, involving diverse comparative analysis such as proteomics, metabolomics, ionomics, hormone levels and cell wall immunofluorescence assays. In ?O'Neal? (a low firmness variety) enhanced levels of aquaporins, expansins and pectin esterases at the green stage were found to be critical in distinguishing it from ?Emerald? (a high firmness variety). The latter featured higher levels of ABA, low methyl esterified pectins in tricellular junctions and high levels of catechin at this stage. In addition, a greater abundance of XET/H, high content of methyl esterified homogalacturonan, together with several mechanisms of cell wall reinforcement such as calcium and probably boron bridges appear to be prominent in ?Emerald? ripe fruit epicarp regarding ?O'Neal?. This study highlights the importance of cell wall reorganization and structure, abundance of specific metabolites, water status, and hormonal signaling in connection to fruit firmness. These findings result particularly valuable in order to improve the fertilization procedures currently used or in the search of molecular markers related with firmness.