Increased Temperatures Promote Fruit Enlargement Through Cellular and Transcriptomic Changes in Raspberries (Rubus idaeus L.) cv. Heritage

Climate change is expected to increase temperatures in agricultural producing regions, potentially affecting fruit development and quality. To date, the molecular responses of raspberry fruits to moderate warming under field conditions have not been explored. In this paper, raspberry plants (Rubus idaeus L. cv. Heritage) growing in two contrasting agroclimatic regions of Chile were exposed to a moderate increase in temperature during fruit development. Fruit phenotyping, histological analyses, and RNA sequencing were used to evaluate physiological and transcriptomic responses to warming. Elevated temperature increased fruit weight and fruit dimensions in both orchards and was associated with larger drupelet and cell areas, which was accompanied by reduced cell density. Moreover, transcriptomic analyses revealed marked differences in gene expression responses between raspberries fruits from different locations with only a small number of heat-responsive genes shared across locations. Nevertheless, the common enrichment of oxylipin-related processes was observed, suggesting a conserved response. In addition, a combined treatment model identified the enrichment of processes like ribosome biogenesis, RNA metabolism, cell cycle regulation, cytokinesis, and structural cellular remodeling. These transcriptional changes were consistent with the cellular phenotypes observed in heat-treated fruits. Overall, our results show that moderate warming promotes larger raspberry fruits through changes in cellular organization, while the underlying molecular responses are strongly influenced by agroclimatic context.