Transcriptomic analysis of CO2-treated strawberries with enhanced resistance to softening and oxidative stress

Identification of molecular determinants underlying the firming effect and protection gainst senescence of high CO2 using diploid strawberries: One of the greatest threats to strawberries is rapid softening, however firmness increases during or following high CO2 levels. Firmness at consumption is an obvious target for preventing fruit loss and to gain eating quality. Therefore, we performed RNA-seq analysis, construcing a weighted gene co-expression network analysis (WGCNA) to identify which molecular determinants play a role in cell wall integrity , using strawberries under storage conditions. Differential gene expression (DEG) analysis showed that cell wall structural architecture of firmer CO2 -treated strawberries is characterised by xyloglucans stabilisation attributed mainly to a down-regulation of Csl-like E1, β-glc, XTH15 and maintenance of expression levels of FUT and GMP as well as improved lamella integrity linked to a down-regulation of RG-lyase and PL-like. The preservation of cell wall elasticity together with the up-regulation of LEA, EXPA4, and MATE transporters required to maintain cell turgor, are the mechanisms controlled by high CO2. In stressed air-cold stored strawberries, in addition to an acute softening, there is a preferential transcript accumulation of genes involved in lignin and raffinose pathways. The oxidative stress involving jasmonate and H2O 2 is characteristic of senescent non-cold stored samples. The results are fundamental and practical for breeding in strawberry industry. The ripe Mara des Bois strawberries (Fragaria vesca) immediately after harvest (2 hours) were used as the control (AH). Those placed directly in a chamber at 20 ºC and 80 % RH for two days were the non-cold stored (NCS), while the strawberries transferred at 20ºC for 1 day following the 7-day storage at 1ºC (conditions employed to simulate a time in transit) were used to analyse the air-cold stored fruit (ACS) or CO2 -cold stored fruit (CCS). CCS were pretreated for two days with a gas mixture containing 18 % CO2 + 18 % O2 + 64 % N2 and then air-ventilated for another five days (CCS).